HUTNICTWO, GÓRNICTWO ›
INŻYNIERIA MATERIAŁOWA ›
2010-3 |
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(Ti, Al)N films on Ti-6Al-4V titanium alloy produced by means of vacuum arc method
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Piotr Wieciński  Jerz y Smolik Halina Garbacz Hideyuki Murakami Krz ysztof j. Kurzydłowski
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Surface engineering methods are effective way to meet the increasing
demands of industry. The needs of increasing efficiency and life
time of the mechanical components lead to looking for a coatings
which are resist to degradation in severe environments and endurance
of extremely high thermomechanical loads [1]. In recent years,
the development of several industrial branches was determined by
the potential of surface engineering, especially of plasma deposition
methods of thin coatings [2÷4]. (Ti, Al)N coating is an example of
thin PVD coatings which are known for more then 10 years. Due
to their high hardness, superior resistance to abrasive and chemical
wear, (Ti, Al)N coatings considerably improve the life time of the
cutting and drilling tools and allow to applied higher working velocities
[5÷7]. Additionally, they exhibit excellent oxidation resistance,
at temperatures higher than 850°C, due to dense alumina layer
which is formed on the surface [8÷10].
(Ti, Al)N phase has B1-NaCl structure, the same as for TiN phase.
Since Al atoms are smaller than Ti, substitution of Ti atoms with
Al atoms results in gradually decreases of TiN lattice parameters
[10] and appearance of the distortions and residual stresses in crystallographic
structure [11]. The hardness of the (Ti, Al)N strongly
depends on the aluminium content in the coating. The hardness and
Young modulus increase, with increasing aluminium content in the
film up to 60÷70%. However, beyond this value mechanical properties
of the coating decreases due to formation of hexagonal wurtzite
phase, which is typical for AlN. According to he authors of [12, 13],
(Ti, Al)N film has B1-NaCl structure when the aluminium content
is below 70%.
One of the PVD technique which is used for deposition of
(Ti, Al)N coatings is vacuum arc method. The main advantages of
this method are: high level of ionizations of the target, presence of
multiple ions, high kinetic energy of ions and high [...]
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A method for evaluation of the size of a grain on non-planar surfaces
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JERZY CHMIELA DAMIA N SŁOTA JAN CWAJNA STANIS ŁAW ROSKOSZ
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In the stereological methods [1÷3], applied to describe the grain size
of polycrystalline materials, images of metallographic specimens or
images of plane sections of three-dimensional model structures are
used. Frequently, it becomes necessary to evaluate the grain size in
finished components, for which, due to their manufacturing technology,
it is impossible to make microsections without destroying
the component. In such cases, the possibility to evaluate the size of
grain on a non-planar surface would be an effective solution. However,
the reference publications do not provide any information in
this respect, while there is an urgent need for such, i.e. study in order
to improve the quality control of many parts, including turbine
blades produced by investment casting.
PHASES OF EVALUATION OF THE GRAIN SIZE
ON A NON-PLANAR SURFACE
Evaluation of the grain size on a non-planar surface is a multiphase
task. In the first place, the grain boundaries must be detected. This
is combined with photographic documentation, including an image
of orthogonal projection of a non-planar surface. Based on the image
of the projection, a quantitative analysis of the structure is performed
in order to determine the necessary stereological parameters
and coordinates of grain boundaries points. The values of stereological
parameters obtained by measuring serve as reference values
for the evaluation of the grain size on a non-planar surface obtained
through approximation of geometric measurements of the real surface
area of the investigated component. The coordinates of grain
boundaries, determined in the orthogonal projection image, provide
a foundation for mapping the image of the structure on an analytical
non-planar surface and for calculating stereological parameters.
A detailed discussion of the particular phases of evaluation of the
grain size on a non-planar surface was based on an example of a test
component presented in Figure 1.
The su[...]
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A note on the kink bands in compressed Ni2MnGa single crystals
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Maciej J. Szczerba Bogusław Major Marek S. Szczerba
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In the last decade Ni-Mn-Ga single crystals had been a subject of
intense structural and magnetic studies, because of their enormous
magnetic shape memory effect (MSM), which is observed when
the alloy possesses a tetragonal or orthorhombic crystal structure
[1÷3]. Large interest has been paid to the Curie temperature and to
the critical temperature of martensitic transformation, where upon
cooling the high temperature cubic phase is replaced by the tetragonal
(orthorhombic) structure [4, 5]. Recently, there has been focused
a greater interest on the mechanical properties of the Ni2MnGa type
alloys of cubic phase, because of their capability to adopt large plastic
strains at high temperatures [6, 7] and hence the effect of the
plastic deformation on the degree of deprivation of the MSM is also
studied [8]. In this context, studies of the brittle-ductile transition
which is observed in the cubic Ni2MnGa single crystals at elevated
temperatures are of particular significance. However, as it was very
recently reported in [9], Ni-Mn-Ga single crystals of both of the
cubic and tetragonal structure, subjected to the room temperature
compression are still capable to accommodate locally small plastic
strains, before they fracture at the strength level of about 1 GPa. It
seems important to make a proposal that the brittle-ductile transition
in these alloys may be strongly correlated with temperature
stability of the mechanism responsible for the accommodation of
these small plastic strains.
In this work, deformation geometry of the discussed accommodation
mechanism will be shown in detail. Basing on the experimental
observations of the Ni2MnGa single crystals compressed at
475 K it will be shown that the accommodation mechanism consists
of a successive nucleation and further propagation of the kink bands
and it is strongly correlated with the appearance of the mechanical
instabilities on the stress-strain curve. The analysis presented i[...]
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AgSnBi consolidated by cyclic extrusion compression
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Maria Richert Jan Richert Agnieszka Hotloś Beata Leszczyńska-Madej Marcin Maślanka Marcin Mroczkowski
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Electrical contact materials are used in a variety of applications,
such as electrical switches, contractors, circuit breakers, voltage
regulators, arcing tips, switch gears and relays. Contact performance
typically regards the three major functions of the switch and
their respective set of dependent variables. During contact operation,
a low tendency for contact welding and a low erosion rate are
required.
The toxic nature of lead and the increasing awareness of its adverse
effect on environment and health have led to the development
of lead-free alloys in recent years. A candidate lead-free electric
contact alloys must fulfill some requirements: suitable melting temperature
and solidification behavior, good wettability, excellent mechanical
properties and very good conductivity, resistance against
wear [1÷3]. The Ag-Bi-Sn alloy is a promising lead-free alloy
because it is superior to other candidates with respect to melting,
wettability and mechanical properties [4, 5]. Internal oxidation of
Ag-Sn alloy is important to prepare Ag-SnO2 electrical contact materials
[6]. This process of reaction diffusion of Ag-Sn-Cu consists
of a few stages. It mainly includes three stages: the first process
is the adsorption and decomposition of oxygen at the surface; the
second one is oxidizing reaction to form SnO2 particles and oxide
band; the third one is diffusion of Cu and CuO formation. Being
pollution-free, silver tin oxide (Ag/SnO2) has been used to replace
toxic Ag/CdO contact materials in last two decades.
In terms of replacing cancerous Ag-CdO, as well as reducing
material and process cost, an attempt has been made to synthesize
Ag-Sn-Bi tertiary system as a new way of production of materials
for the electric contacts [3÷5].
The purpose of this paper is to investigate hardness and microstructure
of Ag-Sn-Bi contact material fabricated by powder metallurgy
and then consolidation by special Cyclic Extrusion Compression
method [7]. [...]
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Al effect on the transport properties of nickel oxide – influence on nickel oxidation
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Nacer Halem Jan Kusiński MARIO ARA ABRUDE ANU Georgette Petot-Ervas
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Although the oxidation of dilute Ni-Al (or Cr) alloys have received
considerable attention [1÷9], gaps in the understanding of the oxidation
mechanism are apparent, mainly at T > 900°C. One can
recall that under ideal conditions, a compact Ni1-xO scale grows,
according to a parabolic law, and it is generally assumed that the
rate controlling factor is the outward diffusion of Ni2+ by a vacancy
mechanism.
In the present investigation, we have studied the oxidation kinetic
of Ni and dilute Ni-Al (0.5 wt. %) alloys and we have compared
the results to those of similar studies performed in the past, with
dilute Al-Ni alloys. The data were analyzed taking into account,
both the transport processes in pure and Al-doped Ni1-xO samples
and a fundamental analysis of transport processes through the oxidation
layer.
Transport properties IN TR ANSITION
MET AL OXIDES
These oxides are p-type semiconductors [10÷19]. The prevailing
defects are cationic vacancies (Vαʹ) with an effective mean charge
-α. Their formation can be described by the following equation:
½O2 <=> OO + Vαʹ + αh- (1)
If KV = [h-]α[Vαʹ]/(PO2)1/2 = exp(-ΔGV/RT) (2)
is the equilibrium constant of Eq. 1, then it follows from the
electroneutrality condition that in the undoped oxide:
[h-] = α[Vαʹ] = AKV
1/(α+1) (PO2)1/2(α+1) (3)
where OO is an oxygen ion in a normal site, h- an electron hole, ΔGV
(= ΔHV - TΔSV = -RT lnKV) the standard free enthalpy of formation
of one mole of cationic vacancy, A = α1/(α+1) and the square brackets
indicate molar fractions.
Electrical conductivity of undoped
and Al (0.11 at. %)-doped Ni1-xO single crystals
The electrical conductivity (σ) of p-type semiconducting oxides in
equilibrium with the surrounding atmosphere is controlled by the
hole concentration (Eqs. 2, 3):
σ = σ0 exp(-ΔHσ/RT) = e μ p (4)
where e is [...]
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Al/SiC composites produced by direct extrusion using the KOBO method
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Jarosław Woźniak Marek Kostecki Włodzimierz Bochniak Andrzej Olszyna
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The constantly increasing interest in metal-ceramic composites has
been inspired by the unique properties of these materials. Their high
strength properties, good wear resistance, ability to work at elevated
temperatures, and low density make them very attractive for the automobile,
spacecraft, aircraft and electronic industries. The amount
of these composites used in the industry increased from 3.6×103 tons
in 2005 to 4.9×103 tons in 2010 [1, 2].
The Al/SiC composites are increasingly used in the automobile
industry for manufacturing the components of car engines. Thanks
to their advantageous properties, the Al/SiC composites supersede
aluminum and its alloys. They are used for the manufacture of pistons,
connecting-rods, and brake plates.
The methods, most often reported in the literature, employed for
producing rods of Al/SiC composites are the extrusion techniques.
In these methods, the material prepared for the extrusion process is a
mixture of appropriate powders, which is consolidated or capsuled.
The consolidation is performed using various techniques such as
e.g. hot-pressing or melt-pressing [3÷5].
A method which permits avoiding the hot-pressing or sintering
operations is the KOBO method, in which a solid material or
a powder mixture is extruded in a press with a reversely rotating
die. Thanks to the rotation of the die, the deformation path of the
material varies during the process.
The KOBO method is particularly advantageous since it permits
reducing the extrusion forces necessary for the composite material
to be fully consolidated [6, 7].
Experimental
The matrix material for the Al/SiC was prepared from a commercial
Al powder with a purity of 99.7% and an average particle size of
6.74 μm (delivered by the Bend-Lutz Co). The reinforcing phase
was made of a SiC powder with a purity of 99.8% and an average
particle size of 0.42 μm (Alfa Aesar Co). The size of the particles
of the powders was selected so[...]
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Analysis of the possibilities of increasing resistance to plastic deformation of new biopolymers by means of modification through radiation
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JERZY CYBO JOANNA MASZYBROCKA JERZY KANSY ADRIAN BARYLSKI
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Operational durability of the polymer-metal kinematic systems
used in technology and endoprosthesoplasty depends to a considerable
degree on the resistance of polyethylene to plastic deformation
and wear [1÷6]. In about 90% of applications, conventional
and the cheapest polymer-metal couples are still used in alloplastic
procedures. In one of such cases, a ca. fivefold reduction of susceptibility
to permanent deformation and tribological wear was obtained
for the polyethylene Chirulen 1120. The effect was a result
of a combined application of small plastic deformation (ef. ≈ 0.2,
initiating the transitions) and electron beam irradiation [7÷9]. Those
factors modified the morphology of the polymer. As a result, in operational
conditions, the thickness of the deformed upper layer of
polyethylene reduced, its degree of crystallinity and reorientation of
the lamellar phase were modified, the degree of structure order increased,
and in consequence, the operational durability improved.
The reference literature of the last decade shows, however, that
in order to increase resistance to wear and ageing, what should be
aimed at is to ensure a very high molecular weight and an appropriate
proportion of crystalline and amorphous phases [10÷13]. In
the shaping of the properties, a more and more significant role of
irradiation with an electron beam is being recognized.
Doses higher than 25 kGy are conducive to decomposition of long
macrochains, spatial arrangement of the structure and UHMWPE
crosslinking. A growing dose, to as much as 150 kGy, causes a very
significant increase of resistance to wear [14, 15]. According to the
presented information from the reference literature, two grades of
polyethylene have been recently introduced to production. Polymers
GUR 1020 and GUR 1050 have replaced Chirulen 1120 of
a molecular weight of ca. 106 g/mole. New materials weigh many
times more: 5·106 and 9.2·106 g/mole, and are intended e[...]
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Analysis of the stress distribution in the nanogrid coatings based on digital representation of the structure
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KONRA D PERZYŃSKI ŁUKASZ MAJOR MAGDALENA KOPERNIK Łukasz MADEJ MACIEJ Pietrzyk
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The multilayered coatings have various demanding applications,
were reliability of the product is crucial. The artificial heart chamber
and its constructional elements, e.g. the aortic valves, is one of
such examples. The tribology rules used in the deposition of coatings
on the substrates are relatively simple. The goal is to obtain as
many coating layers as possible. In the standard deposition process
the first coating is hard, the second is soft, and they repeat periodically.
But this approach is not sufficient and cannot be adapted for
specific applications, such as the heart chamber. In that case the
outer coating has to be biocompatible and permanent natural tissuecoating
connection has to be created. The shape of the chamber and
its elements is quite complicated and many crucial points with the
stress concentration occur. On the other hand, the material of the
chamber cannot be deformed irreversibly. Thus, the requirements
for the substrate-coating-tissue system are strict and the standard
modeling methods of the multicoating system, which represents the
flat boundaries between subsequent coatings, should not be used.
It is due to the fact that the capabilities of these methods to correctly
predict the fatigue and cracking phenomena of the analyzed
specimens are not sufficient. The example of a multilayered specimen
with the flat boundaries is presented in Figure 1. In reality the
boundaries between coatings have irregular shapes. New numerical
models, that can correctly describe the geometry of the boundaries
among layers, have to be developed to account for these irregularities.
Application of the digital material representation is one of the
possible solutions [1, 2].
DIGITAL REPRESENTATION OF THE NANOGRIDS
MATERIALS
Various methods can be used to deposit the nanogrid materials [3].
Development of a correct numerical model to support the expe[...]
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Analysis of titanium sheet bending process
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Janina Adamus Piotr lacki Maciej Motyka ZYGMUNT NITKIEWICZ
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Titanium and its alloys are exceptional structural materials, far outstripping
other in many aspects. Thanks to low specific gravity and
high mechanical strength titanium materials are used whenever the
construction weight and its strength are essential, e.g. in the aircraft
and aerospace industries, for sporting equipment and in medicine
[1, 2]. Furthermore, the value of the elastic modulus of titanium alloys
is approximately half the corresponding value for steel. Thus,
titanium alloys are excellent materials for various types of springs
[3, 4]. Good corrosion resistance in most corrosive environments
warrant the application of titanium elements in chemical and marine
industries, desalination and desulfurization systems, in sewage
treatment plants, geothermal systems etc. Apart from technical applications
titanium and its alloys are often used in medicine and
jewellery because of a good biocompability. Titanium as a material
with the unique mechanical and physical properties is used whenever
common structural materials such as aluminium and steel fail.
Unfortunately, the application of titanium and its alloys is difficult
because of high production and processing costs and the fact
that titanium alloys fall into group of materials which hardly deform,
especially in sheet-metal forming processes. During the forming
of titanium sheets it is necessary to overcome many technological
barriers, which are not reflected in the technical literature.
Bending is one of the most commonly used forming methods of
the titanium elements. It comes down to a stable change in material
curvature by bending or straightening. Bending can be done
on press brakes or stamping presses using bending tools, as a roll
bending, roll form profiling etc.
During bending of the titanium elements it is necessary to take
the following into consideration:
-- titanium, especially its alloys, is characterized by [...]
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Anisotropy of Portevin-Le Chatelier effect in Al-Mg-Mn sheet alloy described by acoustic emission
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Joanna Zdunek Jan Powiec Ja rosław Mizera Wojciech l. Spychalski Krzy sztof j. Kurzydłowski
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The Portevin-Le Chatelier (PLC) effect which was found to occur in
many metal alloys, in particular in aluminium alloys, during tensile
testing at certain temperature range is typical of plastic deformation
instability. It appears as a serration on the stress-strain curves.
Traditionally the PLC bands are examined by indirect methods, for
example by using an extensometer or a strain gauge [1, 2].
The PLC effect is basically understood to be a material property
since it is primary known to arise from the underlying microstructural
processes that govern the plastic deformation kinetics of metallic
solids solution, such as the dynamic interaction between the
gliding dislocations and the mobile solute atoms [3]. There have
also been reports which analyze the PLC effect in terms of microbanding
[4], planar slip [5], test temperature, strain rate and grain
size [6, 7].
Aluminium alloys are known to exhibit an anisotropy of mechanical
properties usually correlated with the crystallographic
texture. Cheng and Morris [7] reported on the relation between
the occurrence of the PLC effect and the anisotropy of mechanical
properties in the Al-Mg alloy. They attributed the intensi[...]
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Application of EFTEM and FIB electron tomography to 3D visualization and metrology of nanoparticles in Inconel 718 superalloy
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Adam KRUK GRZEGORZ CEMPURA BEATA DUBIEL Aleksandra Czyrska-Filemonowicz
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Inconel 718 (IN718) is one of the most common precipitation-hardened
Ni-base superalloys. It belongs to a class of Ni-Fe superalloys,
containing a relatively high content of Fe as well as Ti and Al to
provide γ′, Ni3(Ti, Al) precipitates. It also contains Nb which leads
to precipitation of the tetragonal Ni3Nb phase (γ") [1]. A disadvantage
is that the γ" precipitates have a worse thermal stability than γ′
leading to a faster coarsening rate and to a gradual transformation to
an orthorhombic phase of Ni3Nb (δ) above about 800°C. This limits
the use of the alloy to below about 650°C. The γ" phase occurs in
the form of as elongated, oriented particles (disc-shaped) within the
γ matrix, while the γ′ precipitates are spherical [1, 2].
Transmission electron microscopy (TEM) images give valuable
information about the microstructure and chemical composition of
materials. However, they “only" provide a 2D projection of a 3D
object. Electron tomography was developed to reconstruct objects
in three dimensions (3D) from a tilt series of TEM images. This
technique is well accepted in the life sciences as a method used to
study viruses or cells. The resolution in the reconstructions, however,
is limited to a few nanometers. Electron tomography techniques
have recently been adopted by researchers in materials science [2].
In practice, however, the resolution is still of the order of one to two
nanometers because of the limited stability of the sample holders
and the presence of dynamic diffraction in crystalline solids.
Electron tomography is a technique that uses a transmission
electron microscope (TEM) to determine a 3D structure from any
given asymmetric object [3]. This process can be simply broken
down into 4 steps. First, a series of 2D projection images of the
specimen are recorded and systematically tilted to different angles
in the microscope. Second, these individual im[...]
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Ball milling amorphization and consolidation of NiTiZrNb and NiNbTiZrCoCu alloys
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Jan Dutkiewicz Lidia Lityńska-Dobrzyńska Wojciech Maziarz Tomasz Czeppe Anna Góral Justyna Grzonka
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Amorphous nickel rich alloys have been obtained in recent years by
rapid quenching from the liquid state or by mechanical alloying in
a planetary mill [1÷9]. One advantage of the latter method is that it
makes it possible to obtain new materials from powders of different
elements, which are immiscible in the liquid state. Binary NiTi alloys
subjected to ball milling or severe plastic deformation can be obtained
amorphous [1÷3]. The tendency to form an amorphous structure
depends on the relative values of the deformation temperature
and martensite start (Ms) temperature. Lowering of the deformation
temperature in the range below the martensite finish temperature facilitates
amorphization [3]. Mechanical alloying of Ni60Nb20Zr20
alloy [4] involves two consecutive amorphization reactions, leading
first to the amorphization reaction between Ni and Zr layers and
on further milling consequently a Ni-Nb amorphous phase forms.
The resulting two amorphous phases homogenize at longer milling
times. Multicomponent nickel base alloys can be obtained as bulk
glass at composition of Ni50Co10Nb20Ti10Zr10 (at. %) alloys
with reported large supercooled liquid region of more than 40 K
formed by copper-mold casting. The alloys with 5 and 10 at. % cobalt
possess the highest glass-forming ability [5]. Mechanically alloyed
Ni57Zr20Ti18Al5 alloy powders synthesized by high-energy
ball milling have shown a complete amorphization after 5 h of milling,
even broader supercooled region of 56°C and crystallization
temperature above 500°C [6]. Substitution of aluminum by silicon
[7] also allowed to obtain amorphous Ni57Zr20Ti20Si3 powders by
mechanical alloying of pure Ni, Zr, Ti, Si, and ceramic powder mixture;
the metallic alloy amorphized after 5 hours milling indicating
a good glass forming ability. In [8] Amorphous Ni59Zr20Ti16Sn5
alloys were fabricated by melt spinning and by mechanical alloying
(MA) techniques. Differences in crystallization temperat[...]
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Blood permeability testing of chitosan sealed polyester vascular prosthesis
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MACIEJ GAWLIKOWSKI KAROLINA GORKA ROMAN KUSTOSZ ADAM JAROSZ ANTONI NIEKRASZEWICZ MAGDALENA KUCHARSKA
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The aim of the investigation was to determine blood permeability
through the vascular grafts sealed with chitosan. The measurement
method of water permeability of vascular grafts is specified in appropriate
standard [1]. However the standard’s procedure does not
reflect real prosthesis’ work conditions, particularly when it is applied
as an element of heart assist system [2]. In respect of this it was
intended to perform testing according to distinct procedure giving
more complete representation of vascular prosthesis’ properties and
taking into consideration mechanical extensibility of woven fabric
during work with pulsatile pressure load.
MATERIALS AND METHODS
Vascular grafts
The material of the investigation were BARD 004187 style 6010
vascular prosthesis of 16mm internal diameter [3]. Graft samples
marked as 10 and 20 were sealed with layers based on chitosan.
“10" and “20" runs was sealed with material of relative molecular
mass respectively about 130 kD and 100 kD. Reference samples,
marked as 0REF were not modified in any way.
For testing purposes sample sets together with mounting elements
and soft ring seals were prepared (Fig. 1). In such a set active
graft’s length (intended for contact with blood) was 70 mm and active
graft’s wall area was 35 cm2.
Operating medium
As an operating medium the blood collected from animals with
CPDA-1 [4] anticoagulant was used. Transport of biological material
to the laboratory was performed in temperature of 10°C. Time
elapsed from blood collecting to beginning of the investigation was
about 1.5 h. Biological material’s stability was determined by biochemical
tests (hematocrit level, degree of hemolysis) [5] on the
spot of drawing, directly before and during investigation.
Testing methodology
Vascular prosthesis’ samples were divided in three groups: a, b and
c. In "a" group the grafts were subjected to the test without prelimin[...]
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Capabilities of Al2O3 nanolayer formation on carbon fibers by CVD method
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ANITA OLSZÓWKA-MYALSKA AGNIESZKA BOTOR-PROBIERZ
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Carbon fibers are characterized as materials with low oxidation resistance
in an oxidative environment and chemical reactivity limits
their application in metal-matrix composites. To widen the application
of carbon fibers in a metal composite some form of coating is
needed which may improve their oxidation resistance at high temperatures
and to give the possibility of the fiber/matrix interfacial
reaction control [1÷4]. In fact, several techniques such as chemical
vapor deposition (CVD), physical vapor deposition (PVD), the solgel
method and other modern techniques can be used to provide
coating for carbon fibers.
Alumina coating in comparison with other coatings seems to be
very attractive, simply because of the low precursor material price.
The most frequent technique used to obtain oxide coatings like alumina,
silica, zirconia and titania is the sol-gel method. In the case
of an organometallic solution application, fibers are passed through
a solution and the coating is formed by hydrolysis of the organometallic
compounds. The oxide coating homogeneity and thickness
can be controlled by the appropriate selection of the solution concentration,
immersion time and temperature [1, 3÷7]. Alumina coatings
obtained on the carbon fibers by sol-gel method only partially
prevent the oxidation of carbon because of the presence of pores
[3]. However some authors [6] report that the porous alumina coatings
obtained on fibers by sol-gel act not only as diffusion barriers
(improving the oxidation resistance of carbon fiber and preventing
harmful CF/Al interfacial reactions), but also promote wettability
and relieve thermal stress concentration between the carbon fibers
and the aluminum matrix.
The other technique used to obtain thin al[...]
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Catalytic activity of Ni3Al foils in decomposition of selected chemical compounds
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Paweł Jóźwik Zbigniew Bojar Piotr Winiarek
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Alloys based on the Ni3Al intermetallic phase, as compared to competitive
group of nickel-based superalloys, exhibit high strength for
high deformation velocity at elevated temperature, high resistance
to oxidation and carburization at elevated temperature, and much
better fatigue strength (they crack more slowly than other intermetallic
phase-based alloys). However, common application of these
alloys meets, quite a few technological drawbacks mainly related to
insufficient plasticity and a tendency to brittle cracking [1, 2].
Additionally, Ni3Al-based alloys can be used in the form of honeycomb
structures, which have an advantage in lightweight, highstiffness
and high-strength over bulk Ni-based superalloys. Thus
far, we have successfully fabricated Ni3Al thin foils by cold rolling
of commonly casted ingots without any additional treatment. The
proposed technology allows to obtain foils with thickness even below
50 μm and with micro- and nanograined structure [3, 4].
Methanol is expected to become an alternative energy source
(a fuel) in the near future. It can be easily synthesized from biomass,
natural gas, coal etc., which are more abundant resources than
crude oil [8, 9].
Hexane, as the second analyzed compound in this field of research,
is a component of many products related to the petroleum
and gasoline industries. Nevertheless, as an effect of these applications,
increasing amount of this compound is released to the atmosphere
and possibility of hexane deactivations is important for
environmental pollution reducing.
Above mentioned mechanical properties of Ni3Al thin foils, and
their additional good catalytic properties without any coating, allow
to build microscale power sources and microreactors for air purification
(e.g. MEMS, MECS) [3, 4].
The main purpose of this work was an assessment of catalytic
effects observed while thermodecomposition reactions of methanol
and hexane run over Ni3Al foil surface. Preli[...]
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Catalytic behaviours and electrical conduction changes in BaCeO3 ceramics synthesized by sol-gel method
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ARAB MADJID Franciso Wendell B. Lopez Carlson Pereira de Souza Agnieszka Kopia Bakiz Bahcine JEAN RAYMOND GAVARRI
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BaCeO3 (BCO) ceramics and related perovskite type compounds
were intensively studied because of their high temperature potential
applications (e.g. for fuel cell and electrocatalysis technologies)
[1÷3]. They were regarded as very promising candidates as solid
electrolytes in electrochemical devices such as solid oxide fuel cells
(SOFCs) and gas sensors [4÷6]. These perovskite type structures
were highly interesting mainly because of their high ionic conductivity.
More recently, we found that BaCeO3 exhibited heterogeneous
photocatalytic activities for water splitting [7÷10].
Doped barium cerate materials were also investigated as proton
conductors in humidified reducing atmosphere at intermediate temperature:
these perovskite type materials were also considered as
promising electrolytes for SOFCs [11÷14]. The microstructure and
the presence of carbon dioxide in the ambient atmosphere were also
considered as potential parameters that could condition the conductivity
mechanisms [15]. These oxide materials were also found to
present high interest as catalysts for oxidation reaction because of
their high capacity of oxygen conduction. Recently solid gas interaction
analyses between BCO and methane CH4 in air-CH4 flows
were published [16, 17]. However, in our knowledge, the solid gas
interactions between BaCeO3 and carbon monoxide CO were never
studied.
In this work, we first study the conversion of CO in air-CO gas
mixtures interacting with barium cerate powder, and then we determine
the high temperature electrical conductivity of compacted
pellets of barium cerate. We report a new synthesis method allowing
preparing BaCeO3 perovskite ceramics at moderate temperature
(1100°C). Characterizations are achieved using X-ray diffraction
and transmission electron microscopy. The catalytic properties are
investigated from analyses of emitted gases from Fourier Transform
infrared spectroscopy (FTIR). The electrical properties are studied
[...]
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Characterisation of nanocomposite nc-WC/a-C and nc-WC/a-C:H coatings on oxygen hardened Ti-6Al-4V alloy
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TOMASZ MOSKALEWICZ BOGDAN WENDLER Aleksandra Czyrska -Filemonowicz
|
Titanium and its alloys are often applied in aeronautics, chemical,
petrochemical, marine industries and medicine as structure materials
due to their high specific strength and excellent corrosion resistance
[1, 2]. However, titanium alloys are characterized by poor
tribological properties especially in sliding situations. These include
high and unstable friction coefficients, severe adhesive wear,
susceptibility to fretting wear and a strong tendency to gall when
in rubbing contact with itself and other surface [3]. Deposition of
a low friction and wear resistant coatings by different surface engineering
methods is one of the most prospective means to improve
the tribological properties of the titanium alloys.
Nanocomposite coatings were found to be a prospective for improvement
of tribological properties of materials. Hard and soft
phase were often mixed in order to get a compromise between mechanical
and tribological properties [4]. In this field, many nanocrystalline
metal carbide particles (nc-MeC, where Me = transition
metal) have been used as a hard phase and amorphous carbon,
hydrogen-free (a-C) or hydrogenated (a-C:H) have been used as
a second phase [4÷8].
Carbon-based nanocomposites, where nanocrystalline phase is
embedded into a-C matrix, are considered as a new class of protective
material and found wide range of engineering applications,
such as cutting and machining tools, bearing, pumps, machine and
engine parts [9, 10]. These coatings exhibited high hardness, toughness,
good wear resistance and very low friction in ambient air due
to the lubricious a-C matrix [11÷13].
However, when such coatings are deposited on ‘soft’ substrates,
like commercially pure titanium or Ti-6Al-4V alloy, when the applied
load is high enough the softer substrate can undergo plastic
deformation [14]. Therefore, in a present study nanocomposite
coatings were deposited on a ‘hard’ substrate - oxygen hardened
Ti-[...]
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Characteristics of surface layers produced on austenitic-ferritic stainless steel by low temperature glow discharge nitriding
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Bartosz Gołębiowski Tadeusz Zakroczymski Robert Sobiecki Wiesław Świątnicki
|
Austenitic-ferritic stainless steels are characterized by high strength,
better than those of standard austenitic stainless steels, good ductility,
high resistance to stress corrosion, low thermal expansion and
good weldability.
Moreover, thanks to the presence of austenite which is resistant
to hydrogen corrosion [1], the resistance to the hydrogen-induced
damage of austenitic-ferritic steels is better that that of single-phase
ferritic steels. It has been shown, that duplex steels are however
romoted to the hydrogen embrittlement [2].
Numerous advantages of these steels make them attractive for
many potential applications, e.g. in the food, chemical, petrochemical
and paper industries where they can be used for the manufacture
of components intended for exploitation in aggressive environments,
such as boilers, pressure vessels, installations in the food industry
and mining, pipelines transporting natural gas or oil in contact with
seawater. These conditions may favour the penetration of hydrogen
into the steel, and thereby promote hydrogen corrosion.
A method of reducing hydrogen penetration into steel is to produce
a nitrided layer on the surface [3, 4]. A phase with especially
advantageous properties in this respect is the S-phase (known as
expanded austenite γN [5]), which can increase the resistance to frictional
wear and significantly reduce the penetration of hydrogen [3,
6], without altering the high corrosion resistance of the steel. The
presence of the S-phase formed during the low-temperature nitriding
is manifested in the diffraction spectra as a shift of the diffraction
peaks, (which accompan[...]
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Characterization of friction stir welds of 6013 and 6013/2017A aluminium alloy sheets
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Krzysztof Mroczka Jan Dutkiewicz Adam Pietras
|
The Friction Stir Welding (FSW) takes place due to rotation and
movement of FSW tool. A tool moves the welded materials along its
edges. As a result of the FSW process good quality of a weld is obtained
below the melting point. The FSW weld consists of particular
zones: the weld nugget (area in the centre), thermomechanically affected
zone and heat affected zone. The weld nugget is frequently
surrounded by rings known as an onion microstructure (rings) especially
within the FSW welds of the aluminium alloys of 6XXX
series. The microstructure and properties of the particular zones
depend strongly on the welding parameters [1] and the type of the
welding tool pin and shoulder. For example, a grain size within the
weld nugget was found to depend strongly on the linear velocity
of the tool [2]. The various studies of the aluminium alloys that
underwent friction stir welding show various dislocation densities
within welds’ nuggets [3]. The hardness in the region of the weld
can change in many ways [4, 5].
The welds formed by FSW between the aluminium alloy sheets
and especially between the 6XXX series alloys are much better
than those formed by a high-temperature welding methods like Gas
Metal Arc Welding especially due to lower temperature of welding
[6]. The FSW technology is applied presently for welding of the
aluminium and magnesium alloys as well as copper, steel, composites
and dissimilar materials [7÷10].
The alloys of the 6XXX series are often applied in the constructions
and transportation industry. The 6013 aluminium alloy has
broad application in the production of many car parts like vehicle
structure, wheels, panels and others [11]. The mentioned alloy can
be welded by the means of the FSW method similarly as other alloys
of the 6XXX series [11, 12]. Uzun et al. [13] signaled the possibility
of welding the alloy with steel.
Therefore, the aim of the paper was to analyze the microstructures
and properties of the [...]
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Characterization of titanium nitride layer on titanium alloy
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BARBARA SUROWSKA JAROSŁAW BIENIAŚ
|
Titanium and titanium alloys are widely used at some technical and
medical applications because of their mechanical and corrosion resistance
properties. The Ti6Al4V alloy is the most popular and universal
alloy, for example it find a use for the aircraft parts and for
implants in dentistry and orthopedics [1÷3]. This alloy is produce as
cast and as forging. It belongs to the high strength materials but its
wear resistance is low. Therefore various methods of surface modification
are used [4÷7], e.g. plasma electrolytic oxidation (PEO),
electrophoretic deposition (EPD), vacuum plasma spraying, glow
discharge, plasma treatment, chemical vapor deposition (CVD).
Nitriding of titanium and titanium alloys has been investigated for
many years and is used effectively for protection against wear. In
this paper the TiN+Ti2N+αTi(N) layer deposited by glow-discharge
nitriding on the Ti6Al4V alloy is characterized. This hybrid system
is destined as outer layer or intermediate layer under other ceramic
in biomedical applications and as thin film for adhesive bonding to
polymer composites in aircraft applications.
Materials and methods
The TiN/Ti2N/αTi(N) layer was deposited on the Ti6Al4V alloy
(ASTM grade 5). This hybrid layer was produced by glow-discharge
assisted by nitriding in pure nitrogen atmosphere at 1073 K (800°C)
and 4 hPa pressure for 3 h. The process was carried out with the
use of universal apparatus for different types of thermochemical
treatment under glow discharge conditions at Warsaw University of
Technology [7, 8]. The thickness of coating was about 40 μm.
The phase composition of surface layer was performed by X-ray
diffraction technique (XRD). Microstructure and morphology of thin
film were analyzed by scanning electron microscope (SEM) with energy
dispersive X-ray spectroscopy (ED[...]
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Comparison of structure and morphology of hydroxyapatite films obtained by sol-gel and RF PECVD methods
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Anna Zydorczyk Bożena Pietrzyk Hieronim Szymanowski Sebastian Miszczak
|
In the recent years, increasing number of applications of hydroxyapatite
(HAP) layers as implant coatings have been observed. Due to
its chemical composition, similar to that of natural bones, HAP is
highly valued by the medical environment. The HAP layer causes the
implant to integrate faster into surrounding tissues [1]. Additionally,
it is a layer limiting the penetration of metal ions to organism, and
preventing the immune system response. A number of methods can
be used to produce biocompatible coatings on metals for biomedical
applications: high temperature plasma-spraying, electrophoretic
deposition, laser deposition, micro-arc techniques, magnetron sputtering
and sol-gel techniques [2÷9]. However, each method has its
own limitations, often caused by low adhesion strength to the substrate
and also by difficulties with controlling the phase composition
of the coating during the deposition. In this work HAP layers
were deposited by sol-gel method which provided good control of
film parameters, and by a new PE RFCVD method.
Experimental procedure
In sol-gel method, the calcium-phosphate sol was prepared by dissolving
Ca(NO3)2⋅4H2O and (C2H5O)3PO in ethanol. Next, the solutions
were mixed and aged for 15 hours at 60°C. The HAP layers
were deposited on samples of AISI 316L stainless steel and silicon
wafers by dip-coating method. Samples were withdrawn from sol
with constant speed of 35 mm/min and annealed in air at 500°C[...]
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Composite layers produced on nickel substrate by the PACVD metod with the participation of trimethylaluminum
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JERZY ROBERT SOBIECKI RYSZARD SITEK MICHAŁ TACI KOWSKI TADEUSZ WIERZCHOŃ
|
The PAMOCVD method (Plasma Assisted Metal Organic Chemical
Vapor Deposition) is a combination of two methods of deposition
from a gaseous phase, namely the MOCVD method (Metal Organic
Chemical Vapor Deposition), which is widely used in electronic industry,
and the PACVD method (Plasma Assisted Chemical Vapor
Deposition) in which the electrical activation of gaseous atmosphere
can be done by direct current (DC) or radio frequency current
(RF) or microwave current (MW) [1]. The process conducted
in the gaseous atmosphere, enriched with metalorganic precursors
(MOCVD) and activated by a glow discharge (PACVD), permits
producing layers with unique properties, namely good adherence to
the substrate, advantageous performance properties (wear and corrosion
resistance, heat resistance), and good mechanical properties.
This combined process can produce, e.g. layers of the Ti(OCN) type
[2], CrN layers [3], titanium and nickel aluminides [4], aluminum
coatings [5÷10], ZrO2, or NCD and DLC coatings.
The CVD method with the participation of metalorganic precursors
has already been used for producing aluminum layers since the
end of 1960s (20th century). The use of the reactive atmospheres
enriched with vapors of metalorganic compounds permitted lowering
the process temperature thanks to the low temperature of decomposition
of these compounds. In the production of aluminum
coatings, the most frequently used metalorganic precursors are:
trimethylaluminum [(CH3)Al3] known as TMA [5÷8], [(CH3)2AlH]
(di-methyl-aluminum hydride - DMAH) [5÷10], [i-C4H9)3Al]
(tri-isobutyl-aluminum - TIBA) [5÷7], bis(isobuthyl)(-methylcyclopentadienyl)
aluminum (III) [6], diemethylamine alane DMEAA
- [AlH3N(CH3)2(C2H5)] [6, 7, 9], triimethylylamine alane - TMAA
[6, 7] and triethylamine alane - TEAA [6]. Studies carried out during
the last years were chiefly aimed at seeking new precursors and
examining how they affect the structure and properties of the aluminum
l[...]
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Composition - property relations in low-neodymium Nd-Fe-B-Ti melt-spun alloys
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Marzena Spyra Elżbieta Jezierska Daniela Derewnicka Marcin Leonowicz
|
Modification of the properties of Nd-Fe-B magnets by minor addition
of other elements has been studied since their development in
1984 [1÷4]. For neodymium contents lower than that for the stechiometric
Nd2Fe14B phase, beside the hard magnetic phase, the soft
magnetic phases such as α-Fe, Fe3B and Fe2B is present. Such alloys
are called magnetic nanocomposites [5÷6]. However, deacrease of
the Nd content leads to substantial drop of the coercivity. Thus, we
tried to modify of the microstructure of the alloys by addition of
small proportion of Ti.
In this work the effect of titanium addition was studied for the
alloys content of 7, 8 and 9% at. of neodymium.
EXPERIMENTAL
The initial ingots were prepared by arc melting of pure elements.
The Nd7Fe79-xB14Tix, Nd8Fe78-xB14Tix and Nd8Fe77-xB14Tix ribbon alloys
(x = 0, 2, 4 at. %) were prepared by rapid solidification of molten
alloys by melt-spinning with the roll speed of 20 m/s. The overquenched
ribbons were annealed at 953÷973 K for 20 minutes. The
microstructure of the annealed ribbons was studied using a JEOL
JEM 3010 transmission electron microscope. The phase constitution
was evaluated using X-ray diffraction (XRD) (Philips PW
1140, Co). The magnetic properties were measured using a Lake-
Shore 7410 vibrating sample magnetometer in maximum external
field of 3 T.
RESULTS AND DISCUSSION
Addition of Ti for the Nd-Fe-B alloys generally resulted in increase
of the onset of crystall[...]
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Computer simulation of stresses in coatings obtained in the PVD process
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AGATA ŚLIWA WALDEMAR KWAŚNY LESZEK A. DOBRZAŃSKI
|
Quick development of different industry parts nowadays determines
more requirements concerning engineering materials in the range of
mechanical properties, wear resistance, erosion influence and high
temperature influence.
It is essential to understand phenomena proceeding during production,
treatment and service of the engineering material so that it
meets the requirements. The internal stress phenomenon, resulting
from irregular heating or cooling, during plastic working treatment
in the consequence of phase process at mechanical surface treatment,
pouring and metal and alloy solidification and also during
anti-wear coating deposition has also its impact. One has to perform
various tests to acquire that, from destructive methods to the nondestructive
ones, like the ultrasonic and diffraction methods [1].
The advanced surface treatment technology, especially among
others PVD technology, allows to improve service properties of
tools made from the conventional tool materials, which - if not subjected
to such treatment - in many cases do not meet the requirements
and expectations of tools users. Specifications of the PVD
coatings fabrication process require performing analysis of the process
parameters effect on material the substrate and also interaction
between the coating and material substrate in the intermediate
zone.
The finite element method is commonly used currently in such
branches of science, like: mechanics, biomechanics, mechatronics,
materials engineering, and thermodynamics. All types of simulations
shorten the design process and give the possibility to investigate
the particular factors on the entire model. This is often impossible
to achieve in real conditions or not justified economically. The
finite element method makes it possible to understand better the
relationships among various parameters and makes it possible to
select the optimum solution [2].
Many analyses are performed nowadays using advanced calcul[...]
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Crystallographic orientation of aircraft engines turbine blades made of CMSX-4 single crystal nickel superalloy
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Arkadiusz Onyszko Włodzimierz Bogdano wicz Andrzej Nowotnik Krzysztof Kubiak Jan Sieniawski
|
The aircraft engines turbine blades are considered to be so-called
Flight Safety Parts (FSP). They are subject to exceptional requirements
related to the production process and quality control. They
feature narrow dimensional tolerances and perfect surface quality.
Requirements with regard to metallurgical purity, permissible casts’
gas and shrinkage porosity, crystallographic orientation, phase
composition and relative volume of strengthening phases as well as
heat resistance and high-temperature creep resistance are also strict.
Single crystal blades of nickel superalloys belong to the group of
products most difficult to produce and meeting strictest reliability
requirements [1, 2].
Blades of the first turbine stages and guide vanes made of nickel
and cobalt superalloys are subject to continual modification both
in terms of their chemical composition, heat treatment as well as
manufacturing technology. The manufacture of precise casts of single
crystal blades of complex shape of the blade and locking piece is
a difficult process, belonging to highly advanced technologies. This
applies also to the technology of ceramic moulds exposed to especially
difficult conditions, including increased time of interaction
with a liquid metal. Single crystal blades feature the highest hightemperature
creep resistance as compared with blades obtained in
the process of directional crystallisation or conventional casts of
microstructure composed of equiaxial grains [2÷5].
Single crystal superalloys’ properties depend on the crystallographic
direction taken for studies. Hence the assessment of single
crystal casts’ quality is related to determination of their crystallographic
orientation, which provides the basis for mechanical
properties analysis. It has been assumed on the basis of literature
review, that the value of the angle of direction [001] deviation from
the angle of single crystal superalloys growth cannot exceed 15°.[...]
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Development of [FeCoTaN/TaN]n multilayer films for the simultaneous provision of wear protection and soft magnetic properties
|
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Christian Klever Stefanie Spitz Harald Leiste Klaus Seemann Michael Stüber Sven Ulrich
|
Wear protection coatings produced by physical vapour deposition
techniques are established in engineering applications since the early
1980ies. However, a real-time optical inspection of their current
state in service is impossible in most cases due to non-accessibility.
As an approach to overcome this problem, we recently started the
development of wear protection films with intrinsic sensor functionality
based on the implementation of a magnetoelastic ferromagnetic
phase [1].
The development of soft ferromagnetic thin films is driven by the
increasing trend of miniaturization in many technological applications.
Thin films in which low coercivity is combined with a strong
uniaxial anisotropy, a high saturation polarization, and a high electrical
resistance, are interesting for the use in applications where
high frequency electromagnetic fields are applied, such as microinductors
and transformers with magnetic cores [2]. In particular,
such thin films are generally suited for the use in remote interrogable
sensor applications [3]. As an interesting material class, nanocrystalline
FeCoTMN films have been developed in the past years. In
such films, FeCo grains are refined by the surrounding TMN matrix
which results in the reduction of the coercive fields and considerable
electrical resistance. Additionally, grain growth processes upon
annealing are hindered up to considerable temperatures. For the induction
of a uniaxial ferromagnetic anisotropy, usually an external
static magnetic field is applied, either during film growth or ex-situ
with simultaneous annealing. In numerous studies, FeCoTaN films
were shown to exhibit a combination of properties which is a good
compromise between the above requirements [4, 5].
However, there has been no report available on the optimization
or at least the determination of the mechanical properties of
nanocrystalline
ferromagnetic composite films suitable for applications
in electromagnetic hi[...]
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Development of Ti-based materials for alloplastic implants
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ANDRZEJ ZIELIŃSKI SYLWIA SOBIESZCZYK BEATA śWIECZKO-ŻUREK
|
The Ti-based biomaterials, light materials of highest corrosion resistance
and biocompatibility [1], have also some disadvantages.
They may slowly dissolve and result in serious illnesses if the
Ti-Al-V alloy is applied [2]. The Ti alloys have Young modulus too
high as compared to that of a bone [3], fatigue limit too low [4], and
the bone-implant interface strength too weak [5]. The new no Al
and no V alloys are developed [6].
This paper is aimed at demonstrating the previous results and
current research work in this area made by Advanced Biomaterials
Research Group at the Faculty of Mechanical Engineering, GUT.
EARLY AND LATE REACTIONS TO METALLIC
IMPLANTS
The research is made on possible allergies of patients to titanium
and Ti alloys. The cases of such allergies were discovered in hospital
examinations, mainly for stainless steels but also a case for Ti
alloy was found.
The biodegradation can result from different origin: presence
of bacteria [1÷3], wear of surgical tools, improper material [3, 4].
Even for Ti alloy severe degradation can occur (Fig. 1).
The modelisation of change in biological environment of an implant
following inflammation process and assessment of metallic
ions` release by special tests and sensitive chemical techniques are
performed.
EFFECTS OF BACTERIA ON CORROSION
One of possible determinants of early allergies and inflammation
processes can be presence of bacteria [1, 4, 5]. The exposure tests
in biological environments have shown that different bacteria may
have different and substantial effect on corrosion resistance of titanium
alloy. Especially, in presence of Staphylococcus aureus no important
corrosion occurs and Enterobacter cloacae presence results
in fast corrosion - Figure 2. The results are explained by a model
under elaboration in which biofilm of different thickness, permeability
and distance from a metal surface affects composition and
pH of solution adjacent to a metal, creating c[...]
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Directionally solidified CMSX-4 nickel based superalloys; microstructure, orientation, residual stress, microanalysis
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BOGUSŁAW MAJOR KRZYSZTOF KUBIAK Jan Bonarski Maciej Szczerba Łukasz Major Anna Góral Anna Rakowska
|
Single crystal nickel based superalloys still belong to the most
widely used and reliable materials for the most exposed parts of
gas turbine [1÷5]. Directional solidification (DS) is a technology,
which enables to produce gas turbine blades and vanes with columnar
crystal or single crystal structures. High temperature mechanical
properties of single crystal nickel base superalloy castings are
better than castings with polycrystalline structures [1]. The aims
of producing of the blades as single crystals are to eliminate grain
boundaries which favour creep and ensuring of [001] crystal orientation
with minimum of Young’s modulus that is suitable for thermal
fatigue resistance. The final structure of the castings prepared
by DS is influenced by the parameters of the process, therefore it
is inevitable to map and control them [5]. A large number of the
alloys used rely on carefully tailored compositions and heat treatment
schedules that result principally in a microstructure consisting
of gamma (γ) matrix (FCC crystal structure) and ordered gammaprime
(γʹ) (L12) phases [4].
The aim of investigations was to study microstructure in respect
to its inhomogeneity in different scale, defect of microstructure in
nanoscale, crystallographic orientation measured using X-ray texture
technique as well as residual stress by application of X-ray
method in directionally solidified CMSX-4 nickel-based superalloys
produced using the facilities working at the Rzeszow University
of Technology.
mATERIAL AND METH ODS OF EXAMINATI ONS
Materials for examination were fabricated at the vacuum metallurgy
laboratory of the Faculty of Materials Science and Technology
at the Rzeszow University of Technology by application of the
single crystal casting system. A nickel based superalloy CMSX-4
was produced with the nominal chemical composition as follows:
Cr-5.7; Co-11; Mo-0.42; W-5.2; Ta-5.6; Al-5.2; Ti-0.74; Re-3; Hf-
0.1; Ni-balance.[...]
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DSC examinations of the Al-20 wt. % Zn sand-cast alloy inoculated with Ti-containing grain-refiners
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DI MITRIOS TSIVOULAS TOMASZ CZEPPE WITOLD K. KRAJEWSKI
|
Master alloys (MAs) are added to the melt during casting in order
to achieve as fine and uniform equiaxed grain structures as possible
upon solidification. Their action is enhanced by the presence
of higher amounts of solute in the base alloy [1]. The main concern
for grain refinement is to avoid the formation of columnar or mixed
columnar and equiaxed grains in the cross-section of the cast ingot.
The sole restriction on the grain refinement ability of the master
alloys is imposed by the ingot dimensions and the cooling rate;
a large ingot size and a low cooling rate lead to larger differences
in grain morphology and size between the surface and centre of the
ingot [2].
There are several benefits for a finer cast structure after solidification.
These are, namely, fewer casting defects, easier processing
in the subsequent fabrication stages, higher ductility of the ingot
surface shell, which reduces surface cracking susceptibility, and
higher yield stress of the final wrought products [2].
However, the grain refinement process is affected by several
parameters, such as the quantity of the master alloy added in the
melt, the distribution characteristics of the nucleating particles in
the master alloy and in the melt, the exact compositions of the master
alloy and of the base alloy, the casting speed and temperature,
the ingot dimensions and the cooling rate [1].
Regarding the four master alloys of the present work, the
(Al, Zn)3Ti has not been studied before, while the ZnTi4 alloy was
reported to yield a larger grain size compared to the typical AlTiB
and AlTiC additions [3, 4]. The latter two MAs constitute the most
common refiner additions, with the AlTiB-type reported to be superior
in terms of grain refinement potential compared to AlTiC-type
[2÷5]. This is said to occur due to the lower number of nuclei in the
latter MA-type [2]. Li et al. [6] reported that increasing the amount
of Ti and C beyond the standard contents in [...]
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Effect of Al and Iradditions on surface morphology and topography of FeCrNi coatings
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Barbara Kucharska
|
The magnetron sputtering deposition (MSD) method belongs to the
basic and the most important methods of depositing coatings in vacuum
conditions, PVD [1÷3]. A very valuable advantage of this method
is the possibility of depositing coatings, particularly those of complex
chemical composition, in a broad range of thicknesses, starting from
several angstroms. This method is successfully used for depositing
coatings based on steels, also heat-resistant grades, which include
310S steel. In the chemical composition of this steel are the additions
of Ni (~20%) and Cr (~25%) [4÷6]. For better resistance the chemical
composition are enriched by addition of high melting elements [7, 8].
The properties of magnetron coatings depend on the sputtering
process parameters, which influence the microstructure and
the grain size of coatings [9, 10]. The essential purpose of applying
coatings is to protect the substrate or to modify the properties
of surface. This function can only be fulfilled by coatings that are
tight and exhibit good adhesion to the substrate [11]. These conditions
are applicable in particular to coatings intended for protection
against corrosion in liquid solutions, as well as in high-temperature
oxidation conditions [12÷15]. Also, in corrosion protection, surface
smoothness plays an important role. Low surface roughness and the
absence of surface defects inhibit the build-up of aggressive ions
and deposits that might initiate pit corrosion [16].
The paper presents the investigation of the surface topography of
magnetron coatings based on heat-resisting steel of 310S enriched
Al and Ru additions. The AFM (Atomic Force Microscope), SEM
(Scanning Electron Microscope), and profilometric techniques were
used in the investigation.
material
Coatings of the composition of 310S heat-resisting steel, deposited
on a substrate of the same steel by the magnetron sputtering method,
were examined. The magnetron targets were two discs, eac[...]
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Effect of annealing on the structure and properties of Ni46.4Mn28.5Ga25.1 single crystal
|
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RafaŁ Wróblewski Krzysztof Sielicki Marcin Leonowicz
|
Ferromagnetic Heusler alloys are based on the X2YZ phase. The
first notice on such alloys comes from Friedrich Heusler et al. who
characterized the Cu2MnAl alloy in 1903 [1]. That alloy showed
ferromagnetic properties although none of the components was ferromagnetic.
In 1934 Bradley and Rodgers reported on the effect of heat
treatment of Cu2MnAl alloy [2]. Main conclusion coming from
this work is that the ferromagnetism of the Heusler-based alloys
depends not only on the chemical composition but also on the positions
of neighbouring atoms.
The Ni2MnGa-type alloys due to their magnetic field induced
strain (MFIS), up to 10%, attract attention of the scientists and engineers.
Over ten years of studies, since the first report, the magnetic
shape memory effect (MSME) [3] has brought many publications
on the structure and properties of the Ni2MnGa alloys. Especially
structure of the martensite, its type and forming conditions is an
object of great interest of many researchers. Various heat treatment
procedures were proposed. For example Gaitzsch et al. have found
that annealing at 803 K for 24 h leads in the Ni50Mn30Ga20 alloy to
formation of the 7M martensite [4]. In our previous work we studied
the effect of annealing temperature and the cooling rate on the
structure of the polycrystalline Ni50Mn29Ga21 alloy [5]. It was found
that the final structure strongly depends on the conditions of heat
treatment and the 7M martensite can be produced by annealing [...]
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Effect of chemical composition variation on mechanical properties of 6xxx aluminum alloys
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Grażna Mrówka-Nowotnik Jan Sieniawski
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The 6xxx-group contains magnesium and silicon as major addition
elements. These multiphase alloys belong to the group of
commercial aluminum alloys, in which relative volume, chemical
composition and morphology of structural constituents exert significant
influence on their useful properties [1÷4]. In the technical
6xxx aluminium alloys contents of Si and Mg are in the range of
0.5÷1.2 wt. %, usually with a Si/Mg ratio larger than one. Besides
the intentional additions, transition metals such as Fe and Mn are
always present. If Si content in Al alloys exceed the amount that is
necessary to form Mg2Si phase, the remaining Si is present in other
phases, such as Al-Fe-Si and Al-Fe-Si-Mn particles [1, 5÷13].
The aluminium alloys of 6xxx group have been studied extensively
because of their technological importance and their exceptional
increase in strength obtained by precipitation hardening. The
6xxx aluminium alloys are mostly used in extruded products, as
well as for construction and automotive purposes. The ease with
which these alloys can be shaped, their low density, their very good
corrosion and surface properties and good weldability are factors
that together with a low price these make them commercially very
attractive.
The precipitation of the metastable precursors of the equilibrium
β(Mg2Si) phase occurs in one or more sequences which are quite
complex. The precipitation sequence for 6xxx alloys, which is generally
accepted in the literature [1, 7], is:
SSSS → atomic clusters →GP zones → β″→ βʹ→ β (stable)
Some authors [8] consider the GP zones as GP1 zones while the
β″ is called a GP2 zone. The most effective hardening phase for this
types of materials is β″. The medium strength AlMgSi aluminium
alloys are commonly processed by extrusion. Their extradubility
depends to a large extent on chemical composition, casting condition
and heat tre[...]
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Effect of nanostructure on the Ti Grade2 properties
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Halina Garbacz
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Titanium is the metal of choice for the fabrication of dental and
orthopedic implants due to its excellent biocompatibility and high
corrosion resistance to physiological environment. However, commercially
pure titanium exhibit low strength and wear resistance,
which is related to low hardness. Mechanical properties of the bulk
material can be ameliorated by several hardening mechanisms, e.g.
solid solution (alloying), dispersion strengthening, grain refinement.
Ti6Al4V represents one of the most common α+β alloys [1].
However, its drawback could arise from the alloying elements
with toxic effects. Vanadium ions are classified as toxic [2], inhibit
enzymes or can interact with intercellular components [3]. To overcome
these concerns, the toxic V was substituted by inert Nb to
create the alloy Ti6Al7Nb [4] similar to or with even slightly better
properties than Ti6Al4V.
High strength of metallic implants without using alloying elements
can be achieved by grain refinement of titanium as the
Hall-Petch relation predicts, what was experimentally proven [5÷7].
Severe plastic deformation (SPD) processing aims to get microstructural
refinement to a level not achievable with traditional processing
[8÷10]. Hydrostatic extrusion is one of the SPD methods, which
allows to obtain a significant grain refinement, down to the nanometric
scale. This method is developed in collaboration between the
Warsaw University of Technology and Institute of High Pressure
Physics, Polish Academy of Sciences in Warsaw.
In comparison to the standard SPD methods, the hydrostatic
extrusion (HE), as a method of grain refinement, usually requires
a significant smaller total strain [11]. A number of commercially
pure metals and alloys have been processed by HE at ambient temperature
to evaluate the potential of this method for achieving grain
size refinement. For pure metals, the highest degree of grain size
refinement was achieved in the case of titan[...]
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Effect of rapid solidification on the structure and mechanical properties of Al-4Fe-4Ni alloy
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Anna Kula Ludwik Blaz Makoto Sugamata Grzegorz Wloch
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Aluminum alloys are widely used in constructions of light components
at aerospace and automotive industry. In order to improve the
performance of these materials, especially at elevated temperatures,
novel alloying systems and adequate production processes, are extensively
studied. Among several technologies, the rapid solidification
processes (RS) have been received considerable attention as an
effective way to design modern materials with excellent combination
of the strength, sufficient ductility and other useful properties
[1, 2].
RS materials are characterized by specific features, such as refined
grain size, increased solid solubility of some elements in the
alloy matrix, which often result in the suppression of some precipitates
formation and modification of their morphology.
RS process is a relatively attractive technique for Al-based alloys
containing rare earth metals such as Ce, Y and transition metals
such as Mn, V, Cr, Ni and others. Low solubility of these alloying
elements has restricted the content of alloying elements to low values
at traditional metallurgy processes, as the formation of coarse
intermetallics (30 μm in diameter or larger) deteriorate mechanical
properties [3]. Hence, RS processes are particularly convenient
for the structure refining and modification of the microstructure in
those alloying systems.
It has been reported that the strength of aluminum-transition
metal alloys at room and elevated temperature is improved by
uniform dispersion of fine intermetallic compounds formed under
rapid solidification and high cooling rates [4÷7].
The objective of the present study is to analyze the influence
of rapid solidification process on the microstructure and mechanical
properties of the Al-4Fe-4Ni alloy on the basis of experiments
performed on both RS-material and s[...]
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Effect of selected parameters of the melt-spinning process on the thickness and magnetic properties of Nd-Fe-Al ribbons
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Waldemar Kaszuwara Bartosz Michalski Jerzy Latuch Janusz Rębiś
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The Nd-Fe-Al alloys, first described by Inoue [1] in 1996, are inferior
to Nd-Fe-B magnets as far as the magnetic properties are concerned,
but their great advantage is that they do not need additional
annealing (performed after melt-spinning) to achieve their possibly
good magnetic properties. These properties depend on the cooling
rate of the melted material, and the best values achieve at the
quenching rates at which the ribbons have a thickness of the order
of tenths of millimeter. Magnets of this size could be used directly,
without further treatment, in electromechanical micro-devices or
in the MEMS technique [2]. In the application range so defined,
the melt-spinning processed Nd-Fe-Al alloys can compete with
Nd-Fe-B alloys, since the basic technology of Nd-Fe-B magnets
does not permit producing easily components with a thickness of
the order of tenths of millimeter.
The thickness and properties of the Ne-Fe-Al ribbons can be
modified by controlling the melt-spinning process parameters, such
as the rotational speed of the wheel, the shape and size of the crucible
opening, the temperature of the melted material, and the pressure
of the ejecting gas [3].
It has been demonstrated thus far that rapid cooling (at a wheel
rotational speed of 20÷30 m/s) promotes an increase of the share of
an amorphous phase and gives ribbons with poor magnetic properties.
When cooled at lower rates, the material contains a greater proportion
of crystalline phases and has substantially better magnetic
properties [3, 4].
The microstructure of the Nd-Fe-Al alloys has been described
in many publications [5, 6], but there is no consistency in the interpretation
of the results. At present, we can say that the Nd-Fe-Al
alloys with the best properties contain very small amounts of the
amorphous phase and that their structure is multi-phase and built on
a nanometric level [7].
The aim of the present study was to examine the possibility of
producing [...]
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Electrical studies of phase stabilities in the Ce2O(CO3)2·H2O/CeO2 and LaOHCO3/La2O3 systems
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Bahci ne Bakiz MADJ ID ARAB FRÉDÉRIC GU INNETON LAMIA BOURJA ABDE LJALIL BEN LHACHEMI JEAN-RAYMOND GAVARRI
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To develop new selective sensing devices for gas detection, working
in environmental conditions, we are investigating materials susceptible
to interact successively with H2O (vapor), CO2 gas and finally
with a specific gas such as methane CH4, carbon monoxide CO.
One possible solution for improving the selectivity should be to use
oxide phases highly sensitive to carbonatation or hydration, presenting
successive phases stable at increasing temperatures [1÷6].
Two systems are presently investigated to determine their relative
reactivities with CO2 and H2O: the La2O3-H2O-CO2 and CeO2-H2OCO
2 rare earth based systems. The lanthanum based system presents
a series of phases LaOHCO3, La2O2CO3 and La2O3 stable in three
different temperature ranges [7÷15]. It also presents a high interest
because of the strong capacity of hydration of the oxide phase La2O3.
In addition, we have recently shown that these La2O3, LaOHCO3
and La2O2CO3 phases might present interesting catalytic activities,
in presence of methane-air (CH4-air) and carbon monoxide-air (COair)
flows at various temperatures [16]. The cerium system seems
to behave differently with one stable Ce2O(CO3)2·H2O phase (with
3+ valence for cerium ion) and the CeO2 oxide (ceria) stable under
air with 4+ valence for cerium ion [17, 18]. In the present study, we
focus our attention on the decarbonatation kinetics of the carbonate
phases and on the carbonatation kinetics of the oxide phases:
the main objective of these analyses should be to determine their
electrical sensitivities during gas solid interactions with CO2. These
correlations between phase changes and electrical responses are not
known, and they could deliver interesting informations to develop
miniaturized electrical devices including microsensor or microabsorber
systems.
Exp erim ental detail s
Elaboration
The initial samples were first synthesized following the same approach.
A first step consisted in preparing two c[...]
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Electrodeposition of nanocrystalline Ni-Mo coatings from citrate electrolyte solution
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EWA BELTOWSKA-LEHMAN AGNIESZKA BIGOS PAULINA INDYKA LESZEK TARKOWSKI MARCIN KOT JERZY MORGIEL
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Alloys containing molybdenum, e.g. Ni-Mo, are characterized by
high hardness, high wear, thermal and corrosion resistance as well
as good catalytic properties for hydrogen evolution in alkaline solutions.
They also offer an important alternative to hard chromium
coatings as chromates are known to be highly toxic and according
to EU directive they should be eliminated from manufacturing process,
e.g. in automotive and aviation industries [1]. However, these
alloys are difficult to prepare by conventional thermal methods due
to the large differences in their melting points (Ni - 1455°C, Mo -
2620°C) and their limited mutual solubility [2]. Several techniques
have been proposed for the Ni-Mo alloy preparation: mechanical
alloying, plasma sputtering, gas condensation and electrocrystallization.
Electroplating is a relatively simple, low cost and low temperature
method suitable for mass production, where the substrates of
complex shape can be uniformly plated by coatings with high rate.
However, it is known that molybdenum in a metallic state cannot
be separately electrodeposited from an aqueous solution of its salts,
but it can readily be co-deposited with iron-group metals such as
nickel, forming an alloy. The phenomenon is called induced co-deposition
[3]. The mechanism is still not clearly understood, although
a few hypotheses are presented in literature [3÷6]. The electrodeposition
of Ni-Mo alloys have been extensively investigated [7÷11].
A great number of galvanic baths were studied, e.g.: sulphate, sulpho-
salicylate, acetate, tartrate, pyrophosphate, amonia and citrate.
Most deposits obtained from these baths were poor quality, porous
or cracked and electrodeposition process was not efficient, however
pyrophosphate and citrate electrolytes are the most promising.
In the present work the correlation of electrodeposition conditions
from citrate solution with the coating properties was determined.
The surface morphology as a f[...]
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FEM simulation of superplastic forming of a spherical cap made of Ti-6Al-4V
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PIOTR LACKI JANINA ADAMUS MACIEJ MOTYKA
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The phenomenon known as superplasticity has been observed for
a wide range of materials including metallic alloys such as: titanium,
and aluminium alloys, ceramics, composites and minerals
[6÷8, 11, 12]. Superplastic forming (SPF) is a technological process
that enables large deformation with no loss of material continuity.
Slip along grain boundaries is considered to be the main mechanism
of superplastic forming. Depending on the kind of material and
process parameters it is possible to obtain elongation of up to several
hundred percent. Superplastic forming is used for the materials
with poor formability in conventional conditions or if their degree
of deformation is insufficient. Superplastic forming is particularly
well suited for forming of Ti-6Al-4V titanium alloy. Ti-6Al-4V titanium
alloy is one of the most commonly materials associated with
superplastic forming. It is used for light and highly strong structural
elements in aircraft industry. Superplastic forming processes in
aircraft industry applications require fine-grained equiaxed microstructure
of Ti‑6Al‑4V alloy. In practice, superplasticity conditions
are summarised as a grain size less than 10 μm, low strain rate of
less than 10-3 s-1 and forming temperatures of T ≥ 0.5 Tm, where Tm
is the melting point of the material [13]. Materials for superplastic
forming process need to be specially prepared by hot metal forming
and heat treatment [5, 6].
A design of superplastic forming is much more difficult than
conventional forming processes because of the larger amount of
parameters that have to be taken into consideration and controlled
in narrow range of tolerance. Strain rate is the key parameter
and it requires special attention. This parameter decides whether
the necking and rupture occur in the drawn-part. Titanium alloys
exhibit high dependence of yield stress on temperature and strain
rate [8÷10]. The current design methods of superplasti[...]
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Fluidized Bed Atmospheric Diffusion Treatment (F-A/D-T) – scopes and limitations
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Józef Jasiński Leopold Jeziorski Jarosław Jasiński
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Fluidized Bed Atmospheric Diffusion Treatment of the alloys and
metallic materials during tools and machine parts volumetric heat
treatment gives possibility to the surface layer diffusive saturation
of metallic materials with an interstitial elements. Formation of the
Cr, Zn, Ti, W, Nb coatings and layers using fluidization method is
also known. Technically fluidization effect was used 60 years ago in
the United Kingdom for the precipitation hardening of the aluminium
alloys [1]. In Poland the interest for fluid heat treatment started
in the 1970 [2]. Researches using fluidization technology were
guided mainly by the two units, Institute of Precision Mechanics -
- Warsaw and Materials Science Institute - Czestochowa Univeristy
of Technology. The experiments performed initially by the Institute
of Precision Mechanics were focused mainly on the tools low-temperature
nitriding and oxidizing [3], while Materials Science Institute
in Czestochowa researches were interested in carburizing and
carbonitriding mechanisms and kinetics of tools and machine parts
in the organic and inorganic fluidized beds. Next years, differences
rela[...]
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Gas nitrided layers on precipitation hardened stainless steel
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Paweł Kochmański Jolanta Baranowska
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This paper presents research results of nitrided layers on Sandvik
NanoflexTM stainless steel, known also as 1RK91, which belongs to
precipitation-hardening stainless steel group. This is an ultra highstrength
material with a combined excellent corrosion resistance.
By a simple heat treatment after cold deformation, extremely high
tensile strength levels (2000 MPa and 3000 MPa for wire) in combination
with a good toughness (up to ca. 600 HV) could be obtained.
Achievement of such good mechanical properties is caused
thanks to very fine, submicroscopic precipitations as: Cu, Fe2Mo,
ƞ-Ni3(Ti, Al), R-phase, described in several publications [1÷7].
Due to its special properties, this steel is suitable to manufacturing
very responsible surgical tools. Heat treatment of the steel consists
of two steps, i.e. solutioning (ca. 1050÷1100°C), and precipitation
hardening by ageing at temperature typically 475°C for 4 hours.
This range of hardening temperature overlaps with temperature of
nitriding process, therefore thermo-chemical and heat treatment
could be conducted simultaneously under condition of sufficient
corrosion resistance of the layers manufactured at this temperature.
Although limited studies have been conducted to investigate the
plasma and gaseous nitriding response of 17-4 PH stainless steels
[8÷12], very little work has been done concerning the nitriding behaviour
of Nanoflex steel [13, 14]. Sun and Bell have studied layers
obtained on 17-4 PH with the plasma nitriding at temperatures
between 350 and 450°C [7]. They observed in layers nitrided at
temperatures lower than 425°C “white" and featureless morphology
after etching. The resultant XRD patterns for these layers are typical
of an amorphous like structure, without any distinct reflection
peaks. Frandsen with others [14] successfully nitrided Nanoflex
steel using gaseous process at temperature below 425°C for long
duration time (16÷20.5 h). Obtained by them [...]
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Grain imaging and measurement on cross-section of turbine blade using EBSD and optical methods
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Agnieszka Szczotok Bartosz Chmiela Maria Sozańska
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Turbine blades are termed Flight Safety Parts (FSP). Imaging and
measurement of grain in case of the blades is very important, because
grain size, shape and distribution strongly affect the mechanical
properties of the blades. The size and shape of primary grain
are basic structural criteria for quality evaluation of precision cast
products from nickel-based superalloys.
The evaluation of fine-grained product is of great importance to
metallurgists. This work which has traditionally been carried out
using light microscopy can be performed by means of the electron
backscattered diffraction (EBSD) technique used in the scanning
electron microscope (SEM). EBSD is nowadays capable of undertaking
such a study.
EBSD has been known for many years (the diffraction of electrons
was first observed in 1928 by Kikuchi [1]), but only widely
applied in the last 10 years.
EBSD is now a fast, automated technique which is utilized to
determine microtexture (texture on the scale of the microstructure),
microstructure quantification, grain and phase boundary characterization,
phase identification and strain determination [2÷4].
EBSD is based on acquisition and analysis of Kikuchi diffraction
patterns from the subsurface of a specimen in an SEM. In EBSD
a stationary electron beam strikes a tilted crystalline sample and
the diffracted electrons form a pattern on a fluorescent screen. The
diffraction pattern can be used to measure the crystal orientation,
as well as boundary misorientations, discriminate between different
materials, and provide information about local crystalline perfection.
When the beam is scanned in a grid across a polycrystalline sample
and the crystal orientation is measured at each point, the resulting
map reveals the constituent grain morphology, orientations and
boundaries. Electron backscatter diffraction technique to measure
grain-specific orientations and misorientations was first recorded
more than 20 years ago [5] and[...]
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High and low voltage anodic etching of microand nanocrystalline Ti-based biomaterials
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GRZEGORZ ADAMEK JAROSŁAW JAKUBOWICZ
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Titanium based materials are commonly used as biomaterials due
to their excellent biocompatibility and mechanical properties. In respect
to biomedical applications, usually we are interesting in pure
Ti, Ti-6Al-4V and other alloys as well as Ti-ceramic biocomposites
[1÷8].
To improve biocompatibility, osseointegration or corrosion resistance,
the implant surface improvement is required, which provide
sufficiently high roughness. The rough surface of the implant
for hard tissue applications can be prepared mainly by mechanical
[9] or electrochemical [10, 11] methods. In the electrochemical
process, the material is an anode immersed in the electrolyte, so
the process is called anodic oxidation. The anodic etching can be
made at broad potential range, which results in different oxide type.
The etching usually proceeds in H3PO4 or CH3COOH electrolytes
with small HF or NH4F content. These small additions, usually in
the range of 0.1÷2%, result in increasing current density followed
to enhanced surface dissolution. Additionally, the etching rate can
be substantially improved by decreasing grain size. For nanostructure
materials, the large volume fraction of the grain boundaries
states an easy way for the electrolyte penetration. Atoms, which lie
on the grain boundaries are firstly removed and additionally small
nanograins are easily released from the alloy, resulting in pores formation.
That material has lower density than microcrystalline counterpart
and the etched surface is comparable in morphology to the
metallic foams. Due to large pores, this material is attractive for
strong fixation with bones.
experimental data
In this work, the electrochemical etching was applied to the surface
modification of the microcrystalline Ti, as well as micro- and
nanocrystalline Ti-6Al-4V alloys. The microcrystalline materials
were bought in Godfellow and, nanocrystalline one was prepared
by 48 h mechanical alloying in SPEX 8000 [...]
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Influence of a high-temperature hydrogen treatment on a microstructure and surface fracture in Ti-6Al-4V alloy
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Maria Sozańska
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Hydrogen is a unique alloying element in titanium alloys because,
unlike other elements, it can easily be added and removed without
melting. Titanium and its alloys show the absorbability of almost
60 at. % of hydrogen at 600°C. The limit hydrogen of solubility in
Tiα is very low and does not exceed 0.05 at. % at room temperature.
The limit hydrogen of solubility in Tiβ is much higher and its
maximum value is 48 at. %. Since the beginning of the titanium
industry, a great deal of attention has been paid to control the hydrogen
content at titanium products - above 0.2 ppm. The presence
of hydrogen in titanium alloys usually results in degradation of their
microstructure and properties, as well promote some undesirable
effects such as hydrogen corrosion and hydrogen embrittlement
[1]. Treated usually as a component that has a degrading effect, hydrogen
can also be an alloying component with positive temporary
influence on microstructure and properties of titanium alloys, in
particular the two-phase ones [2÷4].
In the presented work, the results of investigation of division
of lamellar microstructure by hydrogen action are presented and
discussed in detail. The cyclic heat treatment operation with the hydrogen
atmosphere is tested.
MAterial and EXPERIMENTAL Details
Two-phase Ti-6Al-4V alloy with: Al - 6.2 wt. %, V - 4.3 wt. %,
Fe - 0.3 wt. % and Ti - in balance was investigated. The alloy was
annealed at 1100°C for 1 hour and slowly cooled in the furnace.
Principles of high-temperature hydrogen treatment
with cyclic operation in Ti-6Al-4V alloy
In titanium alloys, hydrogen most often appears as[...]
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Influence of boron on the surface microstructure of sintered AISI 316L austenitic stainless steel
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Jan Kazior Tadeusz Pieczonka
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Boron is one of the most suitable element investigated with the aim
to activate sintering of stainless steels powders, whose properties
are strongly influenced by residual open porosity. Due to it high affinity
for oxygen, boron reduces the surface oxide of the powders.
Furthermore, boron is α-stabilizer element and it forms different
types of borides (depending on the composition of the base material)
which react with the matrix producing eutectic liquids at lower
temperatures than those usually adopted for the sintering of stainless
steel, what in consequences increases density [1÷7]. However
there are many factors, beside chemical composition, which influence
liquid phase sintering: particle size, green density, sintering
atmosphere, temperature, time of isothermal holding and heating
rate. Their combined effect makes it more difficult to envisage and
control this process. For small components the control of the heating
rate is sufficient to ensure uniform densification, but for complex
components the densification variation are influenced first of
all by the amount of liquid, which is related to the mutual solubility
of the base and additive. As far as boron is concerned, depending
on its concentration and heating rate, a transient or persistent liquid
phase during sintering is induced and densification variation and
microstructure are changed.
During persistent liquid phase sintering, both primary and secondary
rearrangement occur, which promote a considerable densification.
Near full density can be easily obtained, but the effect
on the mechanical properties is partially (sometimes significantly)
reduced by the boride particles resulting from the solidification of
the eutectic liquid, which remain as an almost continuous network
surrounding the ferrous based grains. Whilst hardness and strength
are increased, ductility and toughness are lower than it could be
expected, since this network constitutes a low energy path[...]
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Influence of casting parameters on thermal properties of bulk metallic glass Cu48Zr36Ag11Ti5
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Piotr Błyskun Jerzy Latuch TADEUSZ KULIK
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Bulk metallic glasses take their structure straight from the liquid. In
opposition to the crystal metallic alloys they possess neither a crystalline
structure nor its defects, such as vacancies, dislocations or
grain boundaries [1]. This causes an extraordinary properties of this
group of materials. As regards to their properties, metallic glasses
differ significantly among each other, because of their sensitivity
to even the slightest change of chemical composition. However, it
is possible to describe same general features. Bulk metallic glasses
exhibit high compressive strength (from 2 to 5 GPa) [2, 3] and relatively
low Young’s modulus (70÷90 GPa) [4], what gives rise to an
ability of accumulating a large amount of elastic energy. Moreover,
they have very high wear resistance [5] that comes not only from
the hardness [6], but also from very high surface smoothness [7].
These materials also exhibit very attractive formability. A characteristic
temperature area of very high viscosity appears during
heating before crystallization of the amorphous structure. This area
is defined as ΔTx and is called a supercooled liquid region. It appears
between the onset temperature of crystallization - Tx and the
glass transition temperature - Tg: ΔTx = Tx - Tg. In this temperature
region metallic glass is very susceptible for plastic deformation
(that may reach 106%) and many little parts can be put together to
produce one complex detail [5]. What is important, the amorphous
structure is not lost after heating for short time [8÷10]. In addition,
the parameter ΔTx is often being used to describe glass forming
ability of a bulk glassy alloy. It means that alloys with higher value
of ΔTx exhibit better glass forming ability. For this reason, the research
effort is focused to find optimal manufacturing parameters of
the glass with the widest supercooled liquid region.
A lack of long range ordering (characteristic for amo[...]
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Influence of initial heat treatment on the structure and creep resistance of austenitic Fe-Ni alloy
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Kazimierz j. Ducki Marek Hetmańczyk
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Austenitic Fe-Ni alloys precipitation-strengthened with intermetallic
phases of type γ′ (Ni3(Al, Ti)) obtain their optimum properties
after multi-stage heat treatment consisting of solution treatment
(or annealing) and various ageing variants. Most frequently
for such type of alloys, solution heat treatment from a temperature
980÷1010°C and single-stage ageing at temperature of 710÷730°C
during 16÷20 h are applied [1÷4]. For some Fe-Ni alloys after solution,
it is recommended to apply two-stage ageing, which consists
of carrying out a controlled cooling cycle between two isothermal
soaking processes [5, 6].
In the presented paper, investigation was initiated concerning the
effect of initial heat treatment on the structure, mechanical properties
and creep resistance of an austenitic Fe-Ni alloy precipitationstrengthened
with an intermetallic phase of the γ′ type.
MATERIAL AND PROCEDURE
The examinations were performed on rolled bars, 16 mm in diameter,
of an austenitic Fe-Ni alloy of A-286 type. The chemical composition
of the material is given in Table 1.
Specimens of Fe-Ni alloy were subjected to tests after two variants
of heat treatment, i.e. solution heat treatment and single-stage
ageing and solution heat treatment followed by two-stage ageing.
Parameters of heat treatment for the investigated Fe-Ni alloy were
determined based on previously carried out studies [7, 8]. For the
investigated alloy after solution heat treatment in the conditions
980°C/2 h/water, two variants of specimens ageing were used for
comparison, i.e.:
-- single-stage ageing (variant A): 715°C/16 h/air,
-- two-stage ageing (variant B) : 720°C/8 h + cooling in the furnace
up to a temperature of 650°C + 650°C/8 h/air.
A schematic course of heat treatment of specimens made of the
investigated alloy is presented in Figure 1.
A static tensile test was carried out using a strength testing machine
MTS-810. The examinations were carried [...]
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Influence of manufacture conditions on the properties of CMSX-4 single crystal castings
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Krzysztof Kubiak Arkadiusz Onyszko Jan Sieniawski Włodzimierz Bogdanowicz Andrzej Nowotnik
|
Single crystal turbine blades of the first turbine stages were casted
of nickel and cobalt superalloys. Beginning of their production requires
significant capital expenditure. It also causes many technological
difficulties. Thus, it is essential to have suitable set of casting
equipments, vacuum furnaces for the heat treatment and last but not
least all the processing know-how. Therefore, only a few foundries
are capable to manufacture such turbine blades. Mass production
of these single crystal parts of an aircraft engines so far has not
been implemented in Poland. The studies performed allow to realize
a production technology for single crystal turbine blades casting
in Research and Development Laboratory for Aerospace Materials
of Rzeszów University of Technology. In practice, precise single
crystal casts are obtained via directional crystallization with the use
of a block starter and spiral grains selector in a ceramic mould. In
the process of monocrystallization the ceramic mould is withdrawn
from the heating zone of the furnace to grow the blade. The grains
in the cast’s starter grow in a columnar way against their spiral selector.
Only one grain survives during competitive growth in the
spiral grain selector. The phenomenon of grains growth ‘competition’
is the basis for this process [1÷3].
A single crystal grain nucleus growing from the spiral selectors
is the beginning of the single crystal crystallisation consisting in
dendrites growth in three orthogonal crystallographic orientations
[001].
The direction of [001] axis is parallel to single crystal’s growth
axis [4÷10].
Intensive examinations of quality assessment methods were carried
out in recent years for single crystal casts of a second generation[...]
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Influence of sintering temperature on morphology of dense bioceramics based on hydroxyapatite derived from porcine bones
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Anna Maria Janus ROMAN MAJOR MAREK FARYNA
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Hydroxyapatite (HAp - Ca10(PO4)6(OH)2) is the major constituent
of mineral phase of human bone. It characterizes itself with high
biocompatibility and has been used in medicine and stomatology
for more than 20 years [1].
Hydroxyapatite can be obtained either by synthesis or by extraction
from natural sources. Commercially available hydroxyapatite
materials are listed in Table 1. Hydroxyapatite derived from porcine
bones has not been commercialized yet, thus its development seems
to be an attractive field of research.
Biocompatibility of hydroxyapatite of porcine origin has been
proved under in vitro and in vivo conditions [2, 3].
Heat treatment significantly influences chemical composition of
the regarded hydroxyapatite derived from the animal bone. Such
observation is proved by the other investigators [4, 5]. The information,
found in literature and concerning influence of the sintering
conditions on the dense bioceramics biocompatibility, however, do
not cover all possible sintering conditions [5÷8].
The aim of the presented work was to examine the influence of
the temperature of sintering process on the hydroxyapatite morphology.
The properties of the investigated materials were afterwards
subject of in vitro biocompatibility investigation.
MATERIALS AND METHODS
Hydroxyapatite of porcine origin was obtained from long porcine
bones. Preparation procedure comprised bones boiling in distilled
water for 24 h, mechanical removal of tissue and spongy parts residues,
leaching out of organic matter with 4 M sodium hydroxide solution
during 48 h at 100°C, rinsing with distilled water in order to
remove NaOH, drying at 120°C to constant mass, milling, sieving
and calcination at 450°C in atmosphere of air for complete removal
of organic matter.
As reference material HA BIOCER synthetic hydroxyapatite
from Chema-Elektromet (Pola[...]
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Influence of Sn, Fe and Ag addition on amorphization and thermal stability of mechanically alloyed CuTiZrNi alloys
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DARIUSZ OLESZA K SYLWIA DĄBROWSKA TADEUSZ KULI K
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There have been many works on the development of new alloy systems
showing enhanced glass forming ability, enabling the formation
of bulk metallic glasses (BMG). Over the past decade, BMGs
have gained considerable attention due to their properties (high
yield strength, hardness and elastic strain limit, relatively high fracture
toughness, fatigue resistance and corrosion resistance) and potential
as new structural materials [1÷3].
Nowadays Cu based bulk metallic glasses are considered as potential
engineering materials due to their good mechanical properties
[4]. Various Cu based alloys have been reported to show the
enhanced glass forming ability, enabling the preparation of bulk
alloys by conventional casting methods [5]. These alloys usually
belong to the CuTiZrNi system, sometimes Hf, Al or Y are also
added. Recently, the influence of Fe, Si, Pb and Sn addition on the
glass forming ability and crystallization of CuTiZrNi BMGs has
been studied [6].
Another possibility of fabrication of bulk amorphous alloys is
consolidation of amorphous powders obtained by melt atomisation
or by mechanical alloying technique. Hot pressing, extrusion or
spark plasma sintering of amorphous powders in the temperature
range between glass transition temperature and onset crystallization
temperature allow the fabrication of bulk amorphous samples.
There are few reports only on the mechanical alloying of the
CuTiZrNi powder mixtures [7÷9], showing the amorphization
possibility in this system. The starting point for many studies is
Cu47Ti34Zr11Ni8 alloy elaborated by W. L. Johnson [10].
In the present work, the influence of chemical composition on
the amorphization and thermal stability of mechanically alloyed
CuTiZrNi elemental powder mixtures was studied. The basic
Cu47Ti34Zr11Ni8 composition was modified by replacing Ni by Sn
and replacing Zr by Ag [...]
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Influence of strain rate and deformation temperature on the microstructure of Inconel X750 superalloy
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Andrzej Nowotnik Jan Sieniawski Grażyna Mrówka-Nowotnik Arkadiusz Onyszko
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A fundamental feature of plastic deformation is the homogeneity
of strain distribution. It is commonly accepted that at low temperatures
and high strains, flow localization may develop and affect the
material ductility. On the other hand, hot-deformation at intermediate
temperatures may also result in localized plastic flow and non-
-homogenous deformation. Flow localization, as a result of substructure
instability and collective motion of a large number of dislocations
characterizes coarse slip or shear banding, Luders bands
and the Portevin-LeChatelier effect. Kink bands and mechanical
twins may also be considered as a individual form of flow localization.
Coarse slip is usually used to describe the localized flow
within individual grains, whereas shear bands traverse many grains
very often without any significant relation to the position of easy
glide systems plane. In pure metals and single phase alloys, shear
bands have been found to be preferential sites for the nucleation of
both static and dynamic recrystallization.
It is widely believed that in age hardenable alloys, shear bands
and dislocation substructure produce preferred sites for nucleation
of precipitates, thus enhancing the nucleation. These same features
also are believed to enhance the particle growth rate during hot deformation
as a result of higher vacancy concentration produced by
intensive straining as well as increased dislocation pipe diffusion.
The study of processes which are associated with dynamic aging
of supersaturated solid solution during hot deformation may turn
out to be very complicated because of the mutual interaction between
dynamic precipitation and the structure resulting from the
deformation process. The contribution of flow localization to the
strain hardening or flow softening and the flow stress-strain behaviour
during hot deformation of precipitation hardenable alloys is
still a subject of extensive research. The interaction between [...]
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Kinetics of phase transformations during tempering of tool steels of a different chromium content
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JERZY PACYNA PIOTR BAŁA JANUSZ KRAWCZYK
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During heating as-quenched martensite, the tempering (of unalloyed,
medium and high carbon steels) takes place in three distinct
but overlapping stages: precipitation of ε carbide, transformation
of the retained austenite into lower bainite and precipitation of cementite.
In steels containing alloying elements contributing to an
effect of secondary hardening (V, Mo, W) a fourth stage (transformation)
occurs: precipitation of MC and M2C-type alloy carbides,
that nucleate independently [1÷4].
The first transformation occurs in the temperature range of
100÷200°C. Metastable ε carbide (Fe2.4C) with hexagonal crystal
structure precipitates from the supersaturated martensite [5÷8].
Precipitation of highly dispersed ε carbide is believed to enhance
strengthening in steel [2, 4].
The second transformation takes place during tempering in the
temperature range of 200÷320°C and this is a transformation of the
retained austenite. As the result of this transformation, a non-homogeneous
mixture consisting of supersaturated ferrite and cementite,
i.e. lower bainite forms [1, 2, 4].
Cementite is formed during the third transformation occurring
during tempering in the temperature range of 200÷420°C. This
results in further decarbonization of the matrix and dissolution of
metastable ε carbides allowing for the recovery of the steel matrix
[4, 7]. The mechanism of the nucleation of cementite is, however,
not fully understood yet. According to Ref. [4] precipitating cementite
nucleates independently or in situ on ε carbide particles. Whereas
according to Ref. [5] cementite nucleates independently, mainly on
grain boundaries of former austenite or on subgrain boundaries of
the newly formed cell structure.
Above 400°C diffusion of alloying elements such as V, Mo and
W takes place. Then, the cementite gradually dissolves to make the
nucleation of MC and M2C carbides coherent with the alloy matrix
possible. This leads to an [...]
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Kinetics of phase transformations of undercooled austenite in tool steels of a different chromium content
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JANUSZ KRAWCZYK JERZY PACYNA PIOTR BAŁA TERESA SKRZYPEK ADAM KOKOSZA
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The chemical composition and microstructure of hypereutectoid
steel influences its most important properties, such as: heat fatigue
resistance, resistance to oxidation and mechanical properties [1],
which in consequence determines functionality qualities of tools
produced of this steel. Depending on the material used certain surface
defects can generate, which eliminate tools from further exploitation
[2]. A retained austenite can also play a significant role.
Retained austenite being a metastable phase, appears to be the main
reason for spalling of indigenous rolls [2]. Hypereutectoid cementite
and changes in a matrix influence tribological properties [3, 4].
Spectroscopic methods can be used for the analysis of such changes,
e.g. for characteristics of cementite precipitates [5]. Possibilities
of applying hypereutectoid steels for tools production can also
be determined by means of the CCT diagrams. E.g. the effect of
hot deformation on phase transformation kinetics of undercooled
austenite was considered in the reference [6]. The knowledge mentioned
above, allows to design hypereutectoid steels (e.g. of a bainitic
matrix) or to estimate possible effects when elements made of
this steel (intended to be of a pearlitic matrix) enter into a bainitic
zone at cooling [7]. The chemical composition analysis of this type
of steel requires also a broad estimation of alloy carbides being
formed in it [8], including the role of a continuous network of secondary
cementite [9, 10]. Thus, a carbon content in those steels can
be optimised with regard to the mechanical properties [11] and its
influence on the microstructure of a steel matrix can be determined
[12]. An interlamellar distance in pearlite substantially influences
functional qualities of steel [13]. The austenitizing temperature [14]
and the cooling rate [15] are decisive when considering the steel
microstructure. Vanadium carbides, especially their influence on
grain sizes, are[...]
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Laser welding of DP steel - characterization of microstructure of steel and welded joint
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Marek Stanisław WĘGLOWSKI Sebastian STANO Władysław OSUCH Grzegorz MICHTA
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Increasing demands on weight reduction, safety and cost have led to
a rapid development in car body engineering. A number of new materials
are being investigated, especially steels of greater strength.
Advanced High Strength Steels (AHSS) are being intensively explored
by the automotive industry [1]. The combination of excellent
structural properties and good formability makes AHSS such as DP
(Dual Phase) steel attractive candidates for light-weight vehicles.
Dual Phase steels, so called because they consist essentially of
a dispersion of martensite in a ferrite matrix, are produced by intercritically
annealing and cooling with rate appropriate to achieve
the desired structure [2]. Apart from the chemical composition, the
microstructure and mechanical properties from the practical point
of view the most important property is weldability of automotive
steels [3]. Traditionally, resistance welding and fusion welding have
been used in the automotive industry. However, the most prospective
welding process in this branch of industry is laser welding. The
main advantages of laser welding are small distortions of the sheets
caused by a small width of HAZ, high welding speed and flexibility
of this process [3].
Kang et al. [4] have shown results of laser welding of DP 600
steel 1.4 mm in thickness. They have performed hardness measurements,
microstructure examination, mechanical properties and
formability tests. The results have shown that the maximum hardness
in the heat affected zone (HAZ) exceeds 350 HV. The maximum
hardness was mainly the result of bainite, ferrite and small
amounts of martensite phase. In another studies [5], High Strength
Low Alloy (HSLA) and DP980 (980 MPa) sheet steels, 1.2 mm in
thickness, were welded with a 4 kW diode laser. For the DP steel
weld formability was much lower than that of corresponding base
metal, due to the formation of soft zones in the outer region of the
HAZ of the welds. Results of DP 600 [...]
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Laws of substructure anisotropy of textured metal materials
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YURIY PERLOVICH MARGARITA ISAENKOVA VLADIMIR FESENKO
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Any metal material with a developed crystallographic texture shows
the substructure anisotropy, i.e. different values of substructure parameters,
measured along different directions. Usually such measurements
are realizable by methods of X-ray diffractometry. Among
substructure parameters, influencing the pattern of X-ray diffraction
and, in particular, profiles of X-ray lines, there are interplanar spacings
of the crystalline lattice, coherent domain size, lattice distortion,
dislocation density. However, it is evident for specialists in
X-ray analysis, that the above simplest definition of substructure
anisotropy needs an additional clarification concerning the term
“different directions". Since all X-ray measurements of substructure
parameters use concrete X-ray lines (hkl), which are reflections
from the corresponding crystallographic planes {hkl}, these
measurements characterize the substructure as it is seen only along
crystallographic axes <hkl>. Therefore, the definition of substructure
anisotropy as applied to a textured polycrystal means, that we
compare substructure parameters, measured along crystallographic
axes of the same type <hkl> parallel to different directions (ψ, φ) in
the system of external coordinates. In the particular case these axes
can belong to the same grain, then measured substructure parameters
characterize the substructure anisotropy, developed in grains
with a concrete orientation under deformation.
When considering the substructure anisotropy of material, references
to orientations (ψ, φ)i of axis <hkl> are sufficient for its characterization,
whereas the description of substructure non-uniformity
of textured material requires to split the distribution of axes <hkl>
into sets, belonging to grains with different orientations, characterized
with Euler angles. At the same time the concept of substructure
anisotropy is close to the concept of substructure non-uniformity in
[...]
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Low cycle fatigue behavior and microstructure of 3rd generation TiAl-based alloy
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Grzegorz Cempura Heinz-Josef Penkalla Florian Schubert Aleksandra Czyrska-Filemonowicz
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Continuous effort over the last decades is emphasized to develop
structural materials that could supply appropriate mechanical properties
at the highest possible temperatures. The increase of operational
temperature is particularly important to achieve higher thermal
efficiency, improvement of acceleration, thrust to weight ratio
and lower fuel usage of modern jet engines, stationary gas turbines
and other high temperature machines[1]. For a gas turbine, increase
of 150°C in the turbine entry, could improve its efficiency of about
5% [2].
In power engineering and aeronautics Ti based alloys are used
among others for compressor discs and fan blades. Ti fan blades are
used in the low-pressure compressor but application of conventional
Ti alloys limits temperature in the high pressure compressor up to
about 550°C because their insufficient oxidation resistance [3, 4].
There is a need to develop the lightweight alloys which could
be used at the temperatures higher than 600°C. Intermetallic bases
alloys have a great potential for application as a structural material
for HT applications, because of low density, high strength and good
oxidation resistance. Their strongly ordered structure and directional
bonding is manifested by their high melting point and Young
modulus. However, a large number of ordered phases are too brittle
for structural applications.
Ti-Al intermetallic based alloys, especially third generation
with the density of about 4 g/cm3 have very promising mechanical
properties. The TiAl alloys may be processed in a similar way like
other metals and alloys: with use of conventional manufacturing
processes like ingot melting, casting, precision casting, forging, and
machining on almost conventional equipment [5].
Third generation of TiAl alloys was developed to be the alternative
to nickel-based superalloys in the temperature range up to about
700°C. Due to addition of 5÷10 at. % Nb those alloys have strength
and weigh[...]
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Low friction MoS2(Ti, W) coatings deposited by magnetron sputtering
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Wojciech Paw lak Bogdan Wendler Piotr Nolbrzak Marcin Makówka Katarzyna Włodarczyk Adam Rylski
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Self-lubrication of graphite or of some metal dichalcogenides (such
as MoS2 or WS2) is a very desired property in many technical applications.
The phenomenon of self-lubrication in these materials is
a result of a very big anisotropy of the crystallographic structure of
these materials. In case of the MoS2-based material the basal planes
of MoS2 elementary cells consist of hexagonal, strong covalent-
-bonded planes of metal atoms between two planes of sulfur atoms.
In a perpendicular direction exist weak Van der Waals interactions
between the neighbouring planes built from sulfur atoms, what
brings about a low shear strength [1, 2].
Limitation of use of grease and oils in friction couples becomes
more and more important due to difficulties with smearing at high
loads and to high costs of recycling of used oils. Nowadays, coatings’
engineering is able to tailor the most outward areas of mating
machine elements to working conditions. Coatings based on MoS2
have been largely used in numerous applications, such as, for example,
ceramic tools for dry machining of stainless steel [3÷6], inserts
for dry high speed milling of steel and grey cast iron [7, 8], ejector
pins used for plastic moulds [4], punches for piercing and fine
blanking of stainless steel [6], in a variety of engine components
such as fuel injection systems, tappets, pistons, piston rings and
bearings [5] and recently also as coatings for gears [9, 10] or for
elements of friction simulator working in real space environment in
a lunar orbiter [11].
On the other hand, pure MoS2 coatings exhibit relatively high
wear during sliding in humid atmospheres or temperatures higher
than 400÷500°C due to heavy oxidation [2]. Many attempts have
been made to extend the range of convenient working conditions.
Firstly, by incorporating different metals atoms into MoS2 matrix,
as, for example: Au, Ni, Pb, Ti, Ta, Cr, Ce, Re, Mo, Cr, Zr, W, Si
[2, 12÷14]. Secondly, by using comp[...]
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Low temperature deformation twinning in channel-die compressed aluminium single crystals evidenced by Acoustic Emission
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Zdzisław Jasieński Andrzej Pawełek Andrzej Piątkowski
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It is commonly believed that twinning is the most efficient source
of acoustic emission [1÷5] due to fast release of great amount of
elastic energy. It is connected with the fact, that the velocity of twinning
dislocations is higher from this of slip dislocations [4], which
results in the increase of contribution of accelerating effects in the
recorded AE impulses. Very often acoustic emission induced by
twinning contains also an audible range. Hence, more or less loud
characteristic knocks during deformation can be heard.
One of the first AE investigations concerned the tensile test of
titanium and its alloys [1], in which it was established, that the AE
activity in Ti was bound with twinning from the beginning, while
in Ti alloys the AE impulses from twinning appeared after a high
degree of deformation. During compression of the γ-TiAl alloy, AE
sources were identified as generally coming from slip, twinning and
the appearance and development of microcracks. It was reported
that “the detailed mechanisms by which moving dislocations create
elastic waves are not fully understood" [3].
Moreover, the problem of twinning in Al has still remained
controversial. In available literature authors did not find any data
on this subject. It is believed quite commonly, that at least in simple
uniaxial strain state - like in a tensile test - twins do not appear in
Al. The aim of this work is to demonstrate, that there are numerous
proofs that in a complex strain state, which occurs in the channel die
compression of single Al crystals at temperature of liquid nitrogen
the twinning processes do occur.
MATERI ALS AND MET HODS
The single crystals of Al and Ag (for comparison) were produced
with the Bridgman method, of which samples of dimensions
10×10×10 mm of orientations {112}<111> and {531}<231> for Al
and {112}<111> for Ag were cut out.
The single crystals were subjected to tests of channel-die compression
at temperature of liq[...]
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Magnetic properties of Fe60Co5Zr10Mo5B20 bulk amorphous and partially crystallized soft magnetic alloy
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MARCIN NABIAŁEK MICHAŁ SZOTA MARCIN DOSPIAL JAROSŁAW JĘDRYKA
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Currently the search for materials with interesting properties is the
subject of considerable attention of electro-machine industry. The
bulk amorphous and nanocrystalline materials (obtained on their
base, across controlled thermal crystallization process) can be rate
to such a group of alloys. Production of bulk amorphous alloys is
complicated and requires following few principles during alloy
composition. Such a principles were posted by Inoue et. al [1, 2].
Inoue showed that alloy composition should consist at least four
types of atoms, base atoms radius should to vary by 12% and heat of
mixing among basic components should have negative value.
Multi-component alloy composition lead to complicated microstructure,
where short range exchange interaction are energetically
more valuable then long range one. Variation in radius of base atoms
leads to large density, which results from higher compaction of atoms
in liquid then in crystalline state. Furthermore, transition from
liquid into crystalline state is connected with growth of volume of
the sample during solidification process. Negative heat of mixing
causes growth of energetic barrier between liquid and solid state
during solidification process. Increase of smelted material viscosity
lead to decrease of atom movement in alloy volume and block crystallization
process. Some of the bulk amorphous alloys based on
iron or cobalt display good soft magnetic properties [3, 4]. Improvement
of these features can be achieved by nanocrystalization [5, 6].
Several methods like classical crystallization based on long-lasting
(under crystallization temperature) heat treatment [7÷9] or unconventional
based on impulse (over crystallization temperature) heat
treatment [10] of a bulk amorphous alloys lead to nanocrystallization.
These methods are expensive and time-consuming. Production
of as cast bulk nanocrystalline alloy can be viable alternative.
In this work the properties of Fe60Co5Zr1[...]
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Manufacturing powder bearings modified with solid lubricant nanoparticles for high temperature applications
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HANNA WIŚ niewska-WEINERT VOL F Leshchynsky MI KHAIL IGNATIEV TOMASZ RYBAK
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With the rapid development of industries and advanced technologies,
more and more mechanical devices are required to work in
high temperature, for example, the various devices used in aviation
and electrical industries, the engine sliding components, and
the mechanical devices in the nuclear industry. The conventional
grease lubricating systems used in the high temperature do not meet
the present requirements, so it is urgent to develop materials with
excellent self-lubricating property from the room temperature to
about 1000°C. Sliney and co-workers prepared several high temperature
self-lubricating sintered materials [1÷4], three typical materials
among which are PS101 (30% Ni-Cr, 30% Ag, 25% CaF, 15%
glass), PS200 (80% Ni-Co-Cr3C2, 10% Ag, 10% BaF2/CaF2), and
PS300(80% Ni-Cr-Cr2O3, 10% Ag, 10% BaF2/CaF2). These materials
show good self-lubricating properties (friction coefficient about
0.1÷0.3) in a wide temperature range.
New advanced materials are generally considered as essential for
the development of novel solid lubricants giving access to high temperature
applications [5]. The nanoparticle solid lubricant materials
have been identified as being of potentially outmost importance for
many industrial high temperature applications, as a consequence
of their original two-dimensional lamellar structure and superior
friction properties. These materials have been identified as strong
candidates for high temperature tribology applications because of
their atomic-scale structure involving strong covalent bonds and
non-compact space filling. Detailed analysis of nanoparticles mechanical
behaviour during sliding is essential to gain understanding
of the complex physical nature of these nanostructures during
friction process. The shape, strength, fracture and interparticle friction
properties of such nanostructures are of great importance. The
nanoparticle ensemble behavior is believed to be identified by continuum
mechanics metho[...]
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Mechanical alloying of Astaloy CrL powders with silicon
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Marek Hebda Jan kazior
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It is well known that in the competition between wrought and Powder
Metallurgy (PM) steels, sintered materials are at an extreme unbeneficial
due to the deleterious effect of porosity on mechanical
properties such as tensile strength, ductility and impact toughness.
Furthermore, the increased alloy level in powder mixture is disadvantage
due to their negative effect on compressibility. For this reason
it is very important to try to explore non traditional strengthening
mechanism for sintered steels [1]. Recently it was discover that
bainitic-austenitic dual phase steels containing silicon are known to
posses high toughness thanks to the presence of a finely dispersed
retained austenite in a carbide free bainitic matrix. The absence of
carbides in retained austenite is due to the effect of silicon on the
bainitic transformation. Such a microstructure is expected to improve
the mechanical properties of porous sintered steels.
High strength bainitic steels have not been as successful in
practice as quenched and tempered martensitic steels, because the
coarse cementite particles in bainite are unbeneficial. However, the
precipitation of cementite during bainitic transformation can be
suppressed by alloying the steel with about 1.5 wt. % Si, which has
very low solubility in cementite and greatly retards its growth from
austenite [2].
The addition of silicon to steel enables the production of a distinctive
microstructure consisting of a mixture of bainitic ferrite,
carbon enriched retained austenite, and some martensite [3], thereby
stabilizing it down to ambient temperature.
The amount of retained austenite present in microstructure depends
on the composition, cooling rate, austenite morphology and
annealing temperature and time. The silicon suppresses the precipitation
of brittle cementite, and hence should lead to an improvement
in toughness. However, the full benefit of this carbide free bainitic
microstructure has frequently no[...]
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Mechanical and acoustic emission behavior in channel-die compressed Mg9Li alloys before and after treatment by HPT method
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Andrzej Pawełek Stanislav Kudela Andrzej Piątkowski Zdzisaw Jasieński Zbigniew Ranachowski Stanislav Kudela
|
The Mg-Li alloys and the composites based on these materials have
been still attractive candidates for light and tough construction
materials for the application in automobile (e.g. car engine housings),
aviation and space industries. The alloys can occur in three
different phase areas. The alloys containing up to 4 wt. % Li consist
of α phase of hexagonal lattice A3 (hcp), while these with above
12 wt. % Li are in the form of β phase, which is cubic A2 (bcc).
The alloys of Li content from 4 up to 12 wt. % are two-phase and
occur as the mixture of α+β phases. The mechanical properties of
the α phase are worse than these of the β phase, which reveals very
good plasticity [1].
The methods of intensive deformation have recently been more
frequently applied [2÷4] in order to obtain ultra fine-grained refinement
which ensures high strength and plasticity as well as prospects
for the superplastic flow of the material in conditions of relatively
low temperatures [2].
The AE technique has been still helpful in the examinations of
deformation mechanisms, particularly regarding the mentioned materials
of ultra fine-grained (nonocrystalline) morphology obtained
after processing with intensive strain methods [2, 3, 7, 8].
The aim of the research was to describe and explain the correlations
between the proceeding of the generated AE signals and
the mechanisms of plastic (or possible superplastic) deformation in
the Mg-Li alloys subjected to compression tests in the channel-die
before and after the application of HPT technique.
EXPERI MENT AL MET HODS
The Mg-9Li alloys were produced within the cooperation with the
Institute of Materials and Machine Mechanics, Slovak Academy of
Sciences, Bratislava, Slovakia. The material was obtained by melting
magnesium and lithium of 99.99 and 99.5 % purity, respectively
in a Ba[...]
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Mechanical and tribological properties of electrodeposited Ni-Mo coatings
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MARCIN kOT EWA BEŁTOWSKA-LEHMAN AGNIESZKA BIGOS PAULINA INDYKA JERZY MORGIEL WIESŁAW RAKOWSKI
|
Hard chromium coatings are widely used in aerospace, automotive,
hydraulic and machinery industry to reduce friction, wear and corrosion.
Electrodeposition is a frequently used technique to deposit
such a coatings because is simple, low cost and low temperature.
Main advantage is to possibility of relatively uniform deposition
on large, complex shape elements. Nowadays hard chromium that
dominates within this group coatings were characterize by good
mechanical and corrosion resistance but the deposition process is
toxic and carcinogenic. Many environmental friendly materials are
proposed to replace electroplated chromium coatings, and one of
them are nickel based alloys coatings - Ni-P [1], Ni-Mo [2], Ni-W
[3] and nanocomposite coatings like Ni-P-Al2O3 [4], Ni-W-SiC [5].
Pure Ni coatings are not hard and wear resistant, but their properties
could be significantly improved by alloying and reducing the grain
size to nanocrystalline structure. It is reported that Ni-Mo deposits
have a good corrosion resistance but there is a lack of tribological
studies. For coating-substrate systems wear is not only determined
by hardness as showed classical theories of friction [6]. Increase of
hardness is usually associated with rise of stiffness and frequently
cause change of deformation mechanisms from plastic to brittle
fracture. Many studies indicate than wear depends on quotient of
hardness H and modulus of elasticity E [7] which is called plasticity
index. This value can be used to quantitatively assess the load that
may be carried on by the coating in the elastic stress regime. Wear
at the elastic state, when abrasive wear dominates is significantly
lower than under plastic deformation.
The value of the contact force that caused plastic deformation of
the coating can be calculated from Hertz theory [8]:
P R R
pl E
l
ind
= 0 68 3 ⋅ ⋅
3 2
2 . π
(1)
where Eind is the reduced modulus of elasticity of coating and the
[...]
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MgH2 and intermetallic hydride nanocomposites synthesized by mechanical ball milling
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TOMASZ CZUJKO ZBIGNIE W ZARAŃSKI
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One of the obstacles to the implementation of the Hydrogen Economy
into automotive industry is a lack of viable hydrogen storage
system. Relatively promising is hydrogen storage system based
on solid state hydrides with high hydrogen capacities exceeding
6 wt. %. However, a number of high capacity hydrides have high
desorption temperatures which are incompatible with the waste heat
generated by an automotive PEM (Proton Exchange Membrane)
fuel cell.
The search for materials that match the DOE criteria for hydrogen
storage materials to be used in automobile applications has been
largely focused on hydride composites in the past ten years [1÷5].
Very recently, it has been shown [4, 5] that the hydrogen desorption
temperature of the composite constituent with the higher desorption
temperature in the systems, substantially decreases linearly with increasing
volume fraction of the constituent having lower desorption
temperature.
In the present work the composite approach is applied to the
MgH2 + FeTi and MgH2 + LaNi5 systems. The composites with
various volume fractions of both constituents were processed by
controlled reactive milling (CRM) in a magneto-mill (under hydrogen
atmosphere). Hydrogen desorption was tested using a Differential
Scanning Calorimeter (DSC) and Temperature Programmed
Desorption (TPD) analysis. The aim of this work is to analyze the
influence of intermetallic additives on magnesium hydrogen decomposition
process in MgH2 + FeTi and MgH2 + LaNi5 composites.
experimental
As-received commercial MgH2 powder (Sigma-Aldrich; ~98 wt. %
purity; the remaining Mg), LaNi5 (Alfa Aesar, hydrogen storage
grade) and cast FeTi intermetallic powder, were mixed to
MgH2 + X wt. % FeTi and MgH2 + X wt. % LaNi5 (where X = 10,
30 and 50) compositions. As a reference MgH2 without additives
was used.
The FeTi intermetallic powder was obtained by melting pre-compressed
Fe and Ti powders mixture and grinding the obtained ingot.
Gr[...]
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MgH2 based composites with LiAlH4 and LiNH2 complex hydrides
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ZBIGNIE W ZARAŃS KI TOMASZ CZUJKO Iwona MaLKA
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The investigation of materials that could match the requirements for
hydrogen storage system to be used in automobile applications has
been mostly focused on complex hydrides in the past few years.
Especially, since the work of Chen et al. [1], Luo [2] and Vajo et
al. [3] on mixtures of LiNH2/LiH, LiNH2/MgH2 and LiBH4/MgH2,
there have been many publications dedicated to complex hydrides
that are thermodynamically destabilized by ball milling with other
hydrides [4÷7].
The advantage of such reactions is that the relatively large enthalpies
of complex hydrides can be decreased by providing an
alternate reaction pathway that liberates hydrogen. It has also been
observed that new phases could be formed during the high-energy
ball milling of different ratios of known hydrides [2, 3].
Very recently, it has been shown [4, 5] that the hydrogen desorption
temperature of the composite constituent with the higher desorption
temperature in the systems, substantially decreases linearly
with increasing volume fraction of the constituent having lower desorption
temperature.
In the present work the composite approach is applied to the
MgH2 + LiAlH4 and MgH2 + LiNH2 systems. The composites with
various volume fractions of both constituents were processed by
controlled mechanical milling (CMM) in a magneto-mill (under
protective argon atmosphere). Hydrogen desorption was tested
using a Differential Scanning Calorimeter (DSC) analysis. The aim
of this work is to analyze the influence of intermetallic additives on
magnesium hydrogen decomposition process in LiAlH4 and LiNH2
composites.
experimental
As-received commercial MgH2 powder (Sigma-Aldrich; ~98 wt. %
purity; the rema[...]
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Microstructural analysis of as-cast single-crystalline CMSX-4 gas turbine blade
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Beata Dubiel Wiktoria Ratuszek Aleksandra Czyrska-Filemonowicz
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Turbine blades are critical components in both aircraft and
stationary gas turbines. They must be capable to withstand extreme
conditions of temperature and stress during operation. The demand
for increase of the operating temperature above 1000°C resulted in
a development of directionally solidified single crystal (SC) superalloys
for gas turbine blades [1÷3]. Single crystal solidification was
achieved by application of helical grain selector between the casting
and chill plate, enabling selection of a single grain, which fills the
whole mould by dendritic growth. Although such superalloys are
called “single crystals", they consist of two phases: γ solid solution
matrix and about 70% volume fraction of γʹ precipitates. Segregation
of chemical elements, which occurs during solidification, leads
to the differences in the microstructure inside dendrite arms and between
them. Dendritic regions consist of γʹ precipitates surrounded
by narrow γ channels, while interdendritic spaces contain coarse irregular
γ-γʹ eutectic islands [3÷6]. Casting of turbine blades in single
crystal form is very complicated and requires definition of optimum
parameters of technological process. Beside the careful inspection
of the presence of casting defects, the quality control of as-cast
blades involves checking of the deviation from the desired crystallographic
orientation, which should be less than 15° [1]. However,
to check in more detail if the solidification parameters of the casting
are properly chosen, the assessment of the microstructure in microand
nanoscale should be performed. The present paper reports the
results of the analysis of the crystallographic orientation and microstructure
of trial casting of CMSX-4 single crystal gas turbine blade
performed within the project on “Dire[...]
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Microstructural evaluation of CMSX-4 superalloy single crystal castings of various geometry
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Anna Szular Arkadiusz Onyszko Maciej Motyka Zenon Lipiński
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The turbine blades and combustion chamber belong to critical parts
of aircraft jet engines. They work under extreme conditions: very
aggressive corrosion environment, high mechanical and thermal
stresses. Therefore the creep resistance is very important criterion
for selection of critical parts materials and methods of their production
[1].
Advances in turbine blade manufacturing were mainly caused
by implementation of directional crystallization in casting process.
This method enabled obtaining columnar grains in castings, elongated
in the main axis direction. This kind of microstructure with
no transverse grain boundaries provides higher creep resistance
of castings. It was found that much better properties characterize
single crystal castings. Casting process of single crystal blades is
analogous to casting process of blades having columnar grains. The
difference is in the beginning of crystallization process - only one
grain properly oriented is selected for further growth [2÷5].
The main parameters controlling single crystal casting quality
are temperature gradient and withdrawal rate of mould (vw). Too
high cooling rate causes crystallization of grains in front of interface
between liquid and solid phases. Whereas too slow mould
removal from the heating zone leads to excessive microstructural
segregation and defects formation in castings. It is considered that
higher temperature gradient (in the accepted range) contributes to
improvement of casting quality. The most often applied values of
temperature gradient are in the range of 3÷6.5°C/mm and withdrawal
rate of about 5 mm/min [6÷12].
Microstructure of most nickel superalloys is mainly composed of
gamma (γ) and gamma prime (γ′) phases. The γ′ phase (Ni3(Al, Ti))
- primary strengthening phase - is coherent with the matrix - γ
phase. The close match in matrix lattice parameter (~0÷1%) combined
with the chemical compatibility allows the ^[...]
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Microstructure and hardness of magnetron sputtering (Cr, Si)N coatings with up to 30 at. % Si
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Justyna Grzonka Ryszard Mania SŁA WOMIR ZIMO WSKI Jerzy Morgiel
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TiN coatings extending the cutting tools lifetime were praised for
their very good adhesion and hardness exceeding those of high
speed steel or even cemented carbides [1, 2]. However, their limited
high temperature resistance for oxidation during high speed
machining turned interest toward those sandwiched with CrN or
multi-layer coatings like TiN/VN or TiN/NbN [3, 4]. The hardness
of the latter exceeds those characteristic for individual layers due
to coherency strains, while vanadium or niobium nitrides prevent
them from premature oxidation [3, 4]. In most cases the TiN is deposited
first to gain advantage of its excellent adhesion to most steel
substrates. Unfortunately the deposition process of multilayer coatings
is a complicated one and in consequence rarely economically
acceptable.
Therefore, as an alternative, a nanocomposite crystalline-amorphous
TiN/Si3N4 coatings were proposed by Veprek et al. [5]. The
idea of nanocrystalline-amorphous composites is based on development
of shear resistant nanocrystallites of transition-metal nitrides
or carbides surrounded by amorphous nitride [5, 6]. The TiN/Si3N4
coatings obtained up to date show large scatter of hardness from
~20 to ~60 GPa being generally well below expectations [7÷11].
The CrN/Si3N4 coatings showed also only moderate hardness increase
from 16 characteristic for CrN up to max. ~34 GPa [2]. Even
as higher gains were expected from the nanocomposite model rising
CrN based coating hardness up to the level characteristic for TiN
seems interesting from practical point of view.
The further development of these interesting nanocomposite
coatings might be achieved only through simultaneous hardness
measurements and detail experimental ver[...]
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Microstructure and kinetics of intermetallic phases growth in Ag/In/Ag joint obtained as the result of diffusion soldering
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Przemysław Skrzyniarz Joanna Wojewoda-Budka Robert Filipek Paweł Zięba
|
Environment protection and improving the quality of joints are two
main bases of the present development of modern technologies of
different materials joining. The environment protection trend came
into being in the 1990’s in the USA and later it also spread over
Europe and Japan. The main aim is working out soldering materials
able to replace the Sn-Pb solders commonly used so far. This
can be obtained by eliminating cadmium and lead which are the
components of soft solder used in conventional soldering process.
Additionally, RoHS 2002/95/EC directive of the European Parliament
and Council of January 27, 2003 orders the member countries
to limit the use of some hazardous substances in electrical and
electronic equipment. Soon another directive was issued: WEEE
2002/96/EC - Waste Electrical and Electronic Equipment referring
to the problem of the used up electrical and electronic equipment
and its reusing, recycling, and other forms of recovery. It imposes
the responsibility for storing and recycling hazardous substances on
the manufactures.
Hence, a lot of information concerning new methods of joining
materials can be found in the literature. The electronic industry is
a good example. Assembly line production of circuits of high integration
scale with many units sensitive to high temperature and
joined in a very short time enforces applying a special soldering
process so that the solder area is as small as possible. Diffusion
soldering meets such requirements. The joint made in this way takes
up 6 times less space than in the case of conventional soldering and
it can work at the temperatures higher than 350°C [1, 2], and it often
shows mechanical and thermal stability at temperatures 2÷3 times
higher than the joining temperature. Moreover, the surfaces to be
joined do not require special preparation, which remarkably shortens
the production time [3]. The example here could be circuits on
the basis of SiC and semiconduct[...]
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Microstructure and magnetic properties of the Cu-1% Co single crystal
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Joanna Czub BEATA DUBIEL WALDEMAR Tokarz ALEKSANDRA Czyrska-Filemonowicz
|
The Cu-Co alloys has been found to be ideal candidates to study the
giant magnetoresistance phenomenon (GMR), originally observed
in thin magnetic films [1], that have focused great research interest.
Such materials can be applied in micro-switching devices and
detection heads in magnetic recording. The GMR phenomenon,
a big change of the electrical resistivity caused by external magnetic
field, is attributed to the spin-dependent scattering that takes
place in the interfaces between magnetic particles and the metallic
matrix in which they are embedded [2÷5]. The films made of the
alloys based on non-magnetic elements (Cu, Ag) with precipitated
ferromagnetic particles (Fe, Co) appear to posses GMR properties
[6, 7]. However, besides the GMR phenomenon, such alloys provide
a unique opportunity to study their basic properties, such their
microstructures and magnetic properties. The purpose of this work
is to present the results of the transmission electron microscopy
(TEM) analysis which provides the real size distribution of Co particles
in the Cu-1% Co single crystal. We report also the results of
the magnetic measurements in connection with the real distribution
of Co particles which allows us to explain the relation between the
size of the Co particle and the magnetic properties.
EXPERIMENTAL DETAILS
In the present study the Cu-1% Co (wt. %) single crystal of the
origin reported in [8] was used. The investigations were performed
on a sample aged at 600°C for 24 hours. The samples for TEM
and magnetic investigations were cut out from the single crystal.
TEM investigations were performed using a JEOL JEM-2010 ARP
microscope on thin foils prepared by the electropolishing method.
Image analyses were carried out using the ImageJ software.
The magnetic properties were measured using a standard vibrating
sample magnetometer in the external[...]
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Microstructure and mechanical properties of friction stir welded Sc-modified Al-Zn-Mg-Cu alloy
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Mateusz Kopyściański Stanisław Dymek Carter Hamilton Marek Blicha rski
|
Conventional Al-Zn-Mg-Cu (7000 series) alloys are widely used in
aerospace applications due to their favorable mechanical properties.
Their strength, the highest among all aluminum alloys, arises from
a high density of minute precipitates produced upon aging. However,
the mechanical properties degrade above 150°C due to the coarsening
and/or dissolution of the strengthening phases within the microstructure.
There is currently strong interest in adding zirconium and
scandium to Al alloys in order to improve the overall performance
of these alloys [1, 2]. Additions of scandium and zirconium to these
alloys can stabilize the microstructure at elevated temperatures and
can augment the mechanical properties through the formation of
fine, secondary strengthening phases such as Al3(Sc, Zr) [3, 4]. Addition
of Zr together with Sc improves the effectiveness of Sc as
an inhibitor of recrystallization and increases the stability of the
alloy during prolonged exposure to elevated temperatures [5]. What
is more, the addition of Zr reduces the susceptibility of the Al3Sc
precipitates to coarsening. Because the nanometer-sized Al3(Sc, Zr)
particles stabilize the microstructure in elevated temperatures, the
potential for enhanced properties following joining operations, such
as friction stir welding (FSW), arises.
Friction stir welded joints display excellent mechanical properties
when compared to conventional fusion welds, and as such, the
aerospace industry is embracing the FSW technology and implementing
its capabilities into their manufacturing sectors [6]. Over
the last fifteen years, numerous investigations have sought to characterize
the principles of FSW and to model the microstructural
evolution [7÷12]. The current status of FSW research pertaining to
aluminum alloys has been recently well summarized by Threadgill
et al. [13]. The following paper contains introductory results on the
characterization of microstructure and mechanical pr[...]
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Microstructure and mechanical properties of model Al – Li alloys treated by SPD
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Bogusława Adamczyk-Cieśla k Jarosław Mizera Krzysztof Jan Kurzydłowski
|
Several commercial aluminum alloys are targeted to be advanced
materials for aerospace technology due to their low density, high
strength and high elastic modulus, as well as excellent fatigue properties.
Since the reduction of density is one of the main requirements
of modern materials used in aerospace applications, the aluminium-
-lithium alloys became more attractive than conventional aluminium
alloys [1÷3]. Studies on Al-Li alloys intended for aerospace
applications have long been carried out, and numerous papers on
this subject have been published [4, 5]. Several commercial aluminium
alloys have been designed to take advantage of the attributes
of lithium, which is the only alloying element that increases the
strength and modulus while decreasing the density of the alloy.
However, the existing commercial alloys containing lithium were
designed to be relatively strong, so that they also contain the usual
alloying elements that ensure precipitation strengthening [6÷8].
Therefore, although the microstructure and mechanical properties
of Al-Li alloys have been extensively studied before, they have still
been a subject of importance in the recent years. This is connected
with new properties of the materials subjected to severe plastic deformation
(SPD) and with their commercial applications. The major
advantage of SPD techniques is their ability to produce micrometer
size subgrains within the originally coarse grains of materials and
alloys [9÷12].
In the present work the evolution of microstructure and mechanical
properties of three aluminum-lithium alloys were examined. The
materials with an ultra fine structure produced by hydrostatic extrusion
were compared with these materials in the initial state.
ma [...]
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Microstructure and mechanical properties of the Cu/SnAuCu/Cu joints
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Joanna Wojewoda-Budka Anna Sypień Anna Wierzbicka-Miernik Andrzej Piątkowski Paweł Zięba
|
The European Union regulations forced the manufactures to limit
the use of certain hazardous substances such as cadmium and lead
in the electrical and electronic equipment and also make them responsible
for its storage and recycling [1, 2]. In a consequence
the lead-free interconnection technology is one of the most active
branches of the nowadays materials science.
PbSn replecements are mainly the tin alloys, among which a special
class are those consisted of tin and noble metals such as copper,
silver and gold. They are possesing two characteristic features - the
high melting point and high concenteration of Sn compared to that
of eutectic PbSn. Moreover, the composition of the lead-free solders
can be described as eutectic or near-eutectic, which ensures
the best manufacturability. The microstructure of these solders is
a mixture of tin and the intermetallic phase (IP). Since both mechanical
and electrical properties of the tin are anisothropic they
are also anisothropic in the case of eutectic solders. Therefore, the
intermetallics may take a form of the inhomogenous structures (for
example Ag3Sn in the shape large plate-like crystals). To avoid of
such IP creation the concentartion of silver in SnAg solder should
be less than 3% wt. and copper should not go over than 0.7% wt. in
SnCu solders. In the case of SnAu solders gold must not exceed the
value of 5% wt. otherwise it leads to the formation of AuSn4 phase
which causes britlle “cold" joint.
Ternary solders are mainly SnAgCu solders (SAC) where the
amounts of silver and copper (corresponding to the eutectic composition)
are 3.5±0.3 and 0.9±0.2 (wt. %), respectively [3÷5]. Other
ternary solder is SnAuCu alloy which may be used as a joining material
for the joints in so-called noble electronics. They are applied
in devices with the highest degree of reliability, such as biomedical
devices. It should be noted that such products after their exploitation
und[...]
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Microstructure and properties of ball milled and hot compacted powder of 7055 aluminium alloy
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Lidia Lityńska-Dobrzyńska Jan Dutkiewicz Wojciech Maziarz Anna Góral Łukasz Rogal Adam Kanciruk
|
7xxx series (Al-Zn-Mg-Cu) aluminum alloys are widely used in
the aircraft industry due to their low density, high strength and
good workability [1, 2]. Their strengthening increases with the
concentration of Zn and is associated with higher density of very
fine precipitates of metastable η′-phase enriched with Zn and Mg.
The high solute (about 8 wt. % of Zn) alloy designated AA 7055
(ALCOA) evokes the highest strength aluminium alloys produced
by ingot metallurgy and is applied as upper wing skin materials in
commercial aircraft [3]. The 7055 composition processed using the
T77 temper provides a microstructure at and near grain boundaries
that is resistant to both intergranular fracture and interglanular corrosion.
Aluminium based materials produced by powder metallurgy
(PM) processing offer a number of interesting opportunities for high
strength applications. Powder metallurgy enables to fabricate high
quality parts close to final dimensions with refined microstructure
as compared with these produced by the conventional ingot metallurgy
[4, 5]. The ball milling applied before the compaction allows
obtaining a very fine microstructure and the extension of the solid
solubility limits of the elements added to the alloy [6]. It results
in improved mechanical and corrosion properties of the compacted
products. PM technology provides more homogenous distribution
of the precipitates and reduces the particle size that makes corrosion
more uniform [7].
The aim of the present investigation was to study the effect of
ball milling and hot pressing on the microstructure and properties of
milled and compacted 7055 aluminium alloy powder.
Exp erimental details
The mixtures of elemental powders of aluminum, zinc, magnesium,
copper and zirconium were used as starting materials to yield (wt.
%) Al - 8% Zn - 2% - Mg - 2.3% Cu - 0.2% Zr compositions corresponding
to 7055 commercial aluminium alloy. The ball milling
of the powder was [...]
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Microstructure investigation of thin films SnO2 produced by pulsed laser deposition
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Agnieszka Kopia
|
The domain of gas concentration measurements - that was until recently
important primarily in industrial technologies - has become
important in atmosphere pollution research and in issues related directly
to households (emission of toxic gasses, such as CO, NOx,
CH4) [1].
A sensor for detecting and measuring gas concentrations should
be characterized by appropriately high sensitivity, selectivity, a short
response time and stability. These requirements led to a fast development
of research on semiconductor-based gas sensors (Tab. 1).
They meet the majority of these requirements and their appeal
is additionally due to the simplicity of their structure and low costs
of production. In series production, thick-layered sensors based
on SnO2 pay the dominant role beside sensors based on sintered
ceramic materials. The role of thin-layered technologies has been
noticeably growing. Slow abandonment of thick-layered sensors is
related to worse utility properties, compared to thin-layered sensors.
The data available in the relevant literature show that high thickness
of a gas-sensitive material is connected with big grain, which leads
to reduction of the resistance of such material, but also to reduction
of the active surface, i.e. of the sensitivity. Thick-layered sensors
are also characterised by lower selectivity. In case of thin-layered
sensors, surface conductivity - highly dependant on their gas environment
- has a considerable share in the electric conductivity. In
such sensors, the sensitivity and detection threshold are improved
and the response time is reduced.
Tin dioxide SnO2 is a material that is most often used in thinlayered[...]
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Microstructure of Al-Cu thin film deposited by MOCVD
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Bartosz Sarapata Anna Zielińska-Lipiec Constantin Vahlas
|
The Al-Cu system is interesting not only because the alloys from
this system are widely used in electronics. The copper rich part
of the phase diagram contains phases which can be used to create
CMAs (Complex Metallic Alloys). CMA is a class of the multinary
alloys in which different phases are formed with crystal structures
based on giant unit cells, containing hundreds, up to more than
thousands atoms per cell. In these giant unit cells, atoms are arranged
in the clusters which create huge complexity materials. Copper
is a stabilizing agent for quasicrytalline ternary phases based on
aluminum, where third element is a transition metal. The ζ-Al3Cu4
phase is isomorphic to the ϕ-Al10Cu10Fe phase, which is known as
a quasicrytaline phase. The γ-Al4Cu9 phase belongs to the family
of the CMAs, however represents one of the simplest structures
and contains “only" 52 atoms in unit cell [1, 2]. The complexity of
the CMAs, offers unique combination of properties such as electrical
and thermal resistance, enhanced optical properties with high
temperature stability etc. The CMAs are found to exhibit excellent
surface properties with respect to wetting, oxidation, corrosion and
friction [3÷7].
Due to this fact it was interesting to investigate a possibility of
creating the Al-Cu thin films by the means of Metal-Organic Chemical
Vapor Deposition (MOCVD) from the Cu-rich part of the Al-Cu
phase diagram. The work program involved processing of single Cu
and Al coatings, followed by coatings from binary Al-Cu system,
preferably the CMA Al43Cu57 phase. Here we present the results of
the binary Al-Cu coatings deposition.
The MOCVD is a method which allows to deposit metallic thin
films at temperatures lower than classical CVD process. It uses
metal-organic compounds as precursors for the elements such as
Al [...]
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Microstructure of Cu-Ag-P alloy layers plasma sprayed on AgSnO2 composite material
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ADRIANA WRONA MARCIN LIS MIECZYSŁAW WOCH MAŁGORZATA KAMIŃSKA
|
Plasma spraying is a method currently widely used mainly in the
aircraft, automotive, armaments industry for spreading metallic and
ceramic layers on construction components working in the extreme
mechanical and thermal conditions. During the plasma spraying the
material in a form of powder or wire melted in plasma arc falls on
the sprayed surface in a form of melted particles [1, 2]. Very high
temperature of plasma stream, at the level of several thousand Celsius
degrees, and the possibility to control power of the plasma torch
in a wide range bring possibility for spraying virtually every kind
of material, provided that it will not undergo process of evaporation
or decomposition. Most often the technique is used to produce coatings
of high-melting metals, oxide materials, nitrides, carbides and cermets.
The basic advantage of sprayed coatings is their high resistance
to abrasion, corrosion, thermal shocks and high-temperature creep resistance.
The additional benefit is high rapidity and repeatability of
the process as well as possibility to join materials of different melting
points and high coherence of the binding layer-basic material.
Current intensity and plasma arc voltage are the basic energy parameters
of the spraying process, reflected by power of the plasma
torch as well as by the type of plasma forming gazes and intensity
of their flow which influence, among others, arc temperature. The
properties of the layers produced in the process are also influenced
by such geometric parameters as the distance between plasma torch
nozzle and surface.
When spraying with powder material also powder shape and
morphology becomes important. Spherical powders are considered
optimal for that application, as they have lower porosity, higher density
and better flow rate than the powders of more developed surface
(rough). In the study the plasma spraying technique was used for
spreading a layer of a binder of Cu-Ag-P type on a composite [...]
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Microstructure of the complex metallic β-Al3Mg2 phase
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ANNA ZIELIŃSKA-LIPIE C BEATA DUBIEL ALEKS ANDRA CZYRSK A-FILEMONOWICZ
|
Aluminium and magnesium are fairly simple metals with close
packed lattices: Mg is hcp, whereas Al is fcc. The phase diagram
of Al-Mg system contains intermetallic compounds. The mixture of
Al/Mg ratio 3:2 atoms yields an extremely complex crystal structure.
The β-Al3Mg2, called also Samson phase (Fd-3mS: ICSD
57964, cF 1168), has cubic lattice with a = 28.242 Å and a unit cell
containing 1168 atoms [1]. It is decorated by a number of large
clusters of atoms, with near icosahedral atoms symmetry, leaving
few atoms in between to fill-in space [2]. The Samson phase has
hardness about 350 HV, Young’s modulus 68 GPa and low density
2.3 g/cm3. This phase is very brittle at room temperature (fracture
toughness K1c is below 0.5 MPa⋅m1/2). Under compressive stress
and temperatures higher than 250°C, β-phase become plastic [3].
Comparison with Al shows the best compromise between strength
and plastic deformation - strength 3 times higher than pure Al and
plastic strain of about 40%. It means that application fields for this
phase are in aeronautic and automotive industry.
Different stability range of the β-Al3Mg2 in Al-Mg phase diagram
is proposed in literature [4, 5]. According to the phase diagram published
by Murray [4], the β-phase has a congruent point at 451°C
and 38.5% Mg. The stability range of this phase extends from 38.5
up to 40.3% Mg in room temperature. On the Al-rich side, β-Al3Mg2
coexists with the α-phase (which is a solid solution of Mg in Al).
On the Mg-rich side, the β-phase coexists with γ-Al12Mg17 and with
R-phase that forms below 350°C by [...]
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Microstructure of the surface layer of a Ti6Al4V alloy and X5CrNi18-10 steel after laser treatment
|
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Magdalena Rozmus -Górnikowska Jan Kusiński Marek Blicharski Roman Major
|
One of the relatively new method of mechanical surface treatments
is Laser Shock Processing (LSP), which introduce strain hardening
and compressive residual stresses into the treated surface layer. LSP
uses laser pulses with pulse duration within the nanosecond range
to modify the surface layers by means of high pressure [1, 2]. Laser
parameters for LSP require power density ≥0.1 GW/cm2 and laser
pulse duration ≤10-6 s.
During the process, the laser beam is directed onto the surface
of the material. The area to be treated is usually covered with two
types of coatings: an absorbing coating, opaque to the laser beam,
for example black paint, placed directly on the surface of the investigated
material, and over this a transparent to the laser beam
coating for example water [3, 4]. Figure 1 shows the scheme of the
Laser Shock Processing.
When the laser beam with sufficient intensity is directed onto the
surface, it passes through the transparent layer and is absorbed by
the black coating. The absorbing coating is vaporized and the vapor
rapidly achieves very high temperatures at which electrons are ionized
and a plasma plume is formed. The rapidly expanding plasma
is confined on the surface of the metal by the layer of water, creating
high pressures. This pressure propagating into the treated material
as a shock wave, can induce microstructural changes and cause high
increase of dislocation density and produce a high residual surface
compressive stresses [5, 6].
The aim of this work was to investigate the effect of Laser Shock
Processing on the microstructure and roughness of the surface layer
of the Ti6Al4V titanium alloy and X5CrNi18-10 austenitic stainless
steel.
MATERIALS AND E[...]
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Modelling of structure changes in continuous deformation conditions using cellular automata
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Dariusz Kuc JERZY GAWĄD
|
Over last decade several successful applications of the cellular automata
(CA) in simulation of DRX can be found in the literature,
e.g. [1, 2]. The CA method leverages computational simplicity
with reasonable ability to provide quantitative results. The paper
is focused on application of multi-scale 2D CAFE method in hot
forming. CAFE approach consists of the cellular automata model
of microstructure development and the thermal-mechanical finite
element (FE) code. Dynamic recrystallization phenomenon is taken
into account in the 2D CA model which takes advantage of explicit
representation of microstructure, including individual grains and
grain boundaries. The pseudo-hexagonal neighbourhood is used as
a context for state transition rule as described in [1]. Flow stress
is the main material parameter in mechanical part of the FE and is
calculated on the basis of the average dislocation density obtained
from the CA model. Some previously published results that were
achieved using this approach appear very encouraging [3, 4].
In the present study, austenitic X3CrNi18-9 steel was investigated.
This specific material was selected to avoid phase transformation
in the lower range of temperatures. The samples were subjected
to the axisymmetrical hot compression test. Flow stress is the main
material parameter in mechanical part of the FE and is calculated
on the basis of average dislocation density obtained from the CA
model. The results attained from the CAFE model were validated
with the experimental data.
CELLULAR AUTOMATA MODEL
In general, any Cellular Automaton is described by a quadruplet:
<L, S, F, N>, where L is the lattice (spatial ordering) of the cells, S
is the state of the cell, F is the state transition rule governing evolution
of the state in consecutive time steps and N is a definition
of the neighbourhood describing the range of the local interactions
between the cells.
In the current work the CA are used for modeli[...]
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Modelling the effect of SiC mass fraction on crystallization of magnesium metal matrix composite; AZ91/SiC
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Janusz Lelito Paweł Żak Józef Suchy Witold Krajewski Halina Krawiec lind say gree r pete r schumache r amir shirzadi kath arina habe r paweł darłak
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Grain size is one of the most important parameter which determined
mechanical properties. Knowing element properties the proper application
regions for it can be chosen to achieve best mechanical
properties and performance. Nowadays simulation software can be
use to predict the element microstructure. Those programs base on
micro-macro model of crystallization. The model consists of partial
differential equations (PDEs) that described the nucleation rate, diffusion
in the casting, casting cooling speed and every single grain
growth rate. Often it is hard to find the theoretical value of the parameters
that appear in those PDEs. It is possible to find them from
experiment. The experimental data that after applying statistical
methods let us find approximated values of the so-called “fitting
parameters" in the mentioned models [1÷4].
AZ91 alloy analyzed in this study is hypereutectic alloy. The
magnesium primary α-Mg phase is dendritic. During crystallisation
there appears eutectic reaction. In this study influence of eutectic
is omitted because magnesium primary phase has most significant
influence on mechanical properties of the casting.
Experimental procedure
Composite casting
The AZ91 alloy was selected as the matrix for the composites. The
chemical composition is shown in Table 1. The reinforcement particles
are silicon carbide with an average diameter of 45 μm. Composite
specimen with 0, 1, 2, 3 and 4 wt. % of SiC particles were
prepared using a liquid mixing and casting process.
Processing of the magnesium composites consisted of mixing
pre-heated SiC particles to 450°C with liquid magnesium melt
stirring and mould casting. About 1.4 kg of composite melts was
prepared in an electric resistance furnace using a steel crucible under
a SF6/CO2 gas atmosphere. The molten AZ91 alloy was held
at 700°C for 1 h. After putting SiC particles composite was stirred
for 2 min, and then cast at 700°C into mould to produ[...]
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Modelling the effect of SiC particle size on crystallization of magnesium metal matrix composite; AZ91/SiC
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PAWEŁ Żak Janusz LELITO JÓZEF S. SUC HY Witold Krajew ski HAl ina Krawiec Katharina Haberl Peter Shumacher Lindsay Greer Amir Shirzadi BEATA GRACZ
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Grain size is one of the most important structural characteristic
that determining mechanical properties. Knowing element properties,
the proper application regions for it can be chosen to achieve
best mechanical properties and performance. Nowadays simulation
software can be use to predict the element microstructure. Those
programs base on micro-macro model of crystallization. The model
consists of partial differential equations (PDEs) that describe the
nucleation rate, diffusion in the casting, casting cooling speed and
every single grain growth rate. Often it is hard to find the theoretical
value of the parameters that appear in those PDEs. It is possible to
find them from experiment. The experimental data after applying
statistical methods let us find approximated values of the so-called
“fitting parameters" in the mentioned models [1÷4].
AZ91 alloy analyzed in this study is hypereutectic alloy. The
magnesium primary α-Mg phase is dendritic. During crystallisation
there appears eutectic reaction. In this study influence of eutectic is
omitted because magnesium primary phase microstructure has most
significant influence on mechanical properties of the casting.
Model description
In the mathematical model it is assumed that heat transfer is governed
by Fourier-Kirchhoff (FK) equation:
∂
∂T = - +
c
q
p cp div gradT τ ρ ρ 1 ( λ ) , (1)
where: T, K - is temperature, τ, s - time; cp, J·kg-1·K-1 - specific
heat, ρ, kg·m-3 - density, λ, W·m-1·K-1 - thermal conductivity,
q = L(dfs/dτ), W·kg-1 - heat of crystallization.
During simulation the temperature change speed is calculated.
Its value consists of two parts: one, that depends on the temperature
gradient and second that is phase change effect. In this article
there is an assumption that simulation runs in one element of the
melt. With this assumption the gradient depend part of FK can [...]
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Multilayer wear resistant hard coating of high temperature working tool steel obtained by vacuum-plasma DUPLEX technology
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Witold Precht Piotr Małek
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The advance surface engineering, especially surface chemical and
structure modification, resulting in modern vacuum-plasma technology
of hard and superhard, mulitcomponent, multilayer, gradient
and nanocomposite coatings for tribological application. In this
work DUPLEX technology, as one of many possible surface engineering
methods for increasing life time of machine parts and coating
tools, was used, also the influence of ion nitriding before coating
on the tribological properties of the coating was investigated.
In the literature we can found not enough bright investigation
results, connected with influence of technological parameters, architecture
and chemical composition on the tribological properties
of coated tools especially for high pressure aluminium alloys casting
form (Fig. 1).
AIM Of THE WORK
The purpose of this work was to investigate the influence of ion
nitriding process before hard coating of high temperature working
steel of the type X37CrMoV5-1 on they structure and tribological
properties, for possibility to apply our technology also for high
pressure aluminium alloys casting form or other forming tools.
EXPERIMENTAL PROCEDURE
The substrate specimens of high temperature working steel of the
type X37CrMoV5-1 (dim 40×4 cm) after chemical and ion cleaning
were coated by ARC PVD method in two different attachement in
KUT and VTD Drezden (Fig. 2a÷c), using parameters showed in
Table 1.
For investigation of structure morphology, roughness, layer
thickness, microhardness, friction and wear coefficients and adhesion
following instruments were applied:
-- for roughness [...]
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Nanocrystallization of NiNb(ZrTi)Al metallic glasses
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Tomasz Czeppe
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Bulk metallic glasses (BMG) are new class of engineering oriented
materials [1]. Different compositions of Ni based Nb containing
amorphous alloys like: NiNbTi, NiNbZr, NiNbTiZr, NiNbZrTiAl,
NiNbTiZrCoCu, NiZrNbHfAl, NiZrTaNb, reveals high glass forming
ability (GFA), high fracture strength and good corrosion resistance
[2÷7]. Due to the small difference between heat of mixing of
Nb and Zr and Ti, Ni based Nb containing glassy alloys may reveal
good ductility [6]. A very uncommon, composition dependent
property is high thermal stability of the amorphous phase in alloys
containing Hf and Ta or Al [7, 8].
In the following paper the melt spun ribbons of composition
Ni58Nbx(ZrTi)1-xAly, (x = 5, 10, 20, 25 at. %, y = 3, 7 at. %), were
investigated. The alloys were studied from the point of view of the
microstructure, crystallization mechanism, phase composition after
crystallization and crystallization kinetics during continuous heating.
The most often applied are methods of the determination of the
kinetics parameters basing on the assumption of the constant transformation
rate at the peak temperature in the DSC experiments,
when at least three different heating rates must be used. These methods
base on the Kissinger [9] and Ozawa [10] equations and let to
determine activation energy of crystallization. Last time however
also the Matusita [11, 12] method, basing on the transformation rate
for one heating rate is quite often presented in papers. The method
was originally invented and verified for the oxide glasses, while the
crystallization process is much slower than in the case of metallic
glasses. The method lets to verify if the activation energy is constant
during the transformation as well as determine m parameter connected
to the crystals growth dimensions. In the following paper the
Matusita method was applied to determine the activation energy in
case of the lower crystallization rate observed in amorphous alloys
containin[...]
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Nanomaterials: friends or foes?
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Małgorzata Lewandowska Agata Roguska
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Nanomaterials are usually defined as engineered materials which
are built of structural elements (grains, layers, fibres, particles) with
a size less than 100 nm in at least one dimension. Such a definition
is relatively broad and include large-scale bulk materials with the
structure controlled at nanoscale (nano-policrystalline materials,
nanocomposites containing nanoparticles attached, incorporated
or fixed into the matrix) as well as free nanoparticles (including
nanowires, nanotubes, nanodots). In the most general and widely
recognised classification, nanomaterials can be divided into the
1-D (nanotubes, nanowires, nanofibres), 2-D (nanolayers) and 3-D
(bulk materials and nanopowders). It should be noted that in the
scientific literature, different terms are used to indicate small-scale
structured materials, including nanomaterials, nanostructured materials,
nanoparticles, nanosized particles, engineered nanostructured
materials etc.
Nanomaterials have attracted significant scientific attention and
have underwent considerable technological progress. The huge interest
in nanomaterials has been motivated by the exceptional properties
currently possessed and the perceived potential properties and
performance of products produced from such materials. The market
for nano-based products is increasing rapidly. Nanomaterials are already
being used in sporting goods, tires, stain-resistant clothing,
sunscreens, cosmetics, and electronics and will also be utilized increasingly
in medicine for diagnosis, imaging and drug delivery.
The list of their potential applications is growing rapidly and one
should expect that the same applies to the population exposed to
interactions with nanomaterials. However, it should be noted that
although research and development programmes on nanomaterials
have been carried out in a number of institutions worldwide, their
focus was mainly on technology, assessment of the properties and
potential applic[...]
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New energy efficient magnesium technology for strip production and its potential
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KAWALLA RUDOLF ULLMANN MADLEN Oswal d Matthias VOGT HANS -PETER
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Magnesium thin sheets have been manufactured in a complex process
from slabs produced by continuous casting by well-known companies
like Elektron in Bitterfeld, Dow and Alcoa since the 20th
century. This conventional method is still being used by firms like
Salzgitter Magnesiumtechnologie and M&B MAG Toronto.
The technology of twin roll casting, which was developed at
the beginning of the 21st century, reduces the production costs by
a substantial amount and is gaining importance worldwide. Numerous
research teams in Australia, China, Germany, Japan and in Turkey
are dealing with it.
Major advantages are the use of cheaper input materials, not having
to use continuously cast input material, that no heating is needed
during rolling afterwards and that less rolling passes are needed to
reach the final dimensions of the sheets. Another characteristic is
the fast solidification (10 times faster than in the continuous casting
of slabs). This leads to a finer-grained microstructure and the reduction
of cavities, pores, segregations and brittle precipitations which
give better formability and a better quality of the final product.
In Figure 1 the conventional method of production of magnesium
thin sheet and twin roll casting are compared schematically.
The conventional method which is represented herein is a highly
productive, extensive production installation with continuous casting,
disconnected roughing and finishing line, decoiler equipment
and a coil box.
The reduction of process steps which the new technology of
producing strips with dimensions closer to the final product with
twin roll casting creates is, as mentioned above, mainly caused by
not having to use the costly roughing process including mechanical
treatment of slabs.
Table 1 gives an overview of the producing and production similar
twin roll casting plants for the manufacturing of magnesium thin
sheet. Small laboratory installations are not being accounted for.
All[...]
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New tool materials based on Ni alloys strengthened by intermetallic compounds
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PIOTR BAŁA
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Tool steels containing from 0.30% to 0.60% C, up to 5% Cr and
Mo, W and V are universally applied as tool materials for operations
in high temperature. Tools made of these steels obtain functional
qualities by means of heat improvement, it is by combining
quenching procedures with medium or high tempering. Tempering
of tool steels is usually done in the temperature range: 550÷620°C.
Strengthening is achieved by precipitating alloy carbides of MC and
M2C (V, Mo and W) type [1÷4].
Several tools have to operate at temperatures above 600°C,
sometimes even at 1000°C, at which quenched and tempered steels
soften and the lifespan of tools rapidly decreases.
The chemical composition of tool steels was, for many years,
modified to improve their hot-working properties. The combined
alloys Cr-Ni-Co-Fe with additions of W, Mo, Nb, in which a significant
part of iron was substituted by Co were developed [5]. A
group of alloys based on the Co matrix (Stellite) of good tribological
properties intended for cutting tools was obtained. Those alloys
can be divided into certain main groups: Co-Cr-W-C and Co-Cr-
W/W-Ni/Fe-C with modifications Si + B [6, 7]. Unfortunately, the
maximum temperature range in which those alloys can operate is
only 600÷750°C.
A development of high temperature creep-resisting nickel-base
alloys was mainly the modification of 80% Ni and 20% Cr alloy
known for its good creepresistance. On account of ineffectiveness
of strengthening by carbides in high temperatures a hardening of
Ni-base alloys was obtained by intermetallic compound Ni3(Ti, Al)
marked as γ´ [8, 9].
Several alloys were developed based on the concept of Ni matrix
strengthened by the γ´ phase, among others alloys of an increased
carbon content and a complex chemical composition [10÷12].
There are alloys of Ni matrix - intended for tools operating at
temperatures above 600°C - containing from 0.10% to 0.25% C,
from 8 to 25% Cr, up to 25% Co, up to 4[...]
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Nickel aluminate spinel (NiAl2O4) in Al2O3-Ni composites
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Katarzyna Konopka
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Ceramic materials are toughened by incorporating particles of
a ductile metal [1, 2]. Toughness of such composites is due mainly
to plastic deformation of the metal particles (the bridging effect)
and the deflection of cracks by these particles [1]. Which of these
effects predominates depends on the bonds between the metal particles
and the ceramic matrix. If the ductile particles are weakly
bonded with the ceramic matrix, the crack will propagate along the
interface, whereas when this bond is strong, plastic deformation of
the metal particles predominates [3].
Among metals Ni is chosen as particles incorporated to the ceramic
matrix for its high melting point. During sintering in an oxygen
environment (high partial pressure p(O2)), Ni can react with Al
and oxygen from the Al2O3 ceramic or from the gaseous phase and
forms the NiAl2O4 spinel phase according to the reaction [3]:
Ni + Al2O3 + 1/2O2 = NiAl2O4 (1)
The stability of the spinel phase depends on the oxygen partial
pressure in the protective atmosphere, and on the sintering temperature
[3, 4]. When the oxygen partial pressure is low, the NiAl2O4
will eventually reduce to nickel, alumina and oxygen after its formation
[4]. The formation of the spinel can be avoided by conducting
the sintering process in argon, CO or H2 [3].
The more complicated is the process of phases formation in composites
when first the Ni particles are oxidized during the process of
forming or sintering. After the oxidation of Ni the spinel can also be
formed as a reaction [5]:
Al2O3 + NiO = NiAl2O4 (2)
In the solid-state formation of the spinel the so-called Wagner
mechanism is operated [6]. According to this mechanism Ni2+ ions
diffuse through the spinel layer from NiO/NiAl2O4 interphase to the
NiAl2O4/Al2O3 boundary. This reaction leads to formation of one
equivalent of NiAl2O4 on the NiO side of the interface and three
equivalents of spinel on t[...]
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Numerical simulation of microstructure and internal stresses of the modified bone cement
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JERZY NOWACKI ADAM SAJEK
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Hip joint belongs to the most exploited carrying joints in the human
motor organ [1]. Static and fatigue strengths affect the size of
transferred stresses and overload capacity whereas the surface condition
and its physical and chemical features determine the nature
and the strength of joint at the border of bone-implant phases [2, 3].
Even though implantology gives possibilities of replacing damaged
anatomical structures, it restores the lost functions only for a certain
period of time. A reason of that is a wear and tear of artificial joints,
which leads with time to a repeated failure of function [4÷7].
The bone cements are modified with many agents that improve
their operational properties, with a modifying agent participating
in polymerization reaction or being inactive. Addition of reactive
modifying agents, apart from affecting strength properties, can also
decrease the intensity of heat released during mixture hardening
through extension of the reaction time or reduction of the amount
of toxic MMA monomer being liberated into human organism after
cement hardening [8, 9]. Gentamicin containing cements used so far
show that within a certain time interval a drug is released from them
into environment. Some authors are of the opinion that gentamicin
release takes place by the diffusion of compounds through polymer
matrix or capillary through the empty spaces inside it [10]. Nevertheless,
a considerable part of scientists examining the phenomenon
of drug release from bone cements think that it strongly depends on
surface roughness [11÷13].
Until now, the phenomenon of gentamicin release has been closely
examined. When comparing popular cements containing gentamicin
used at present, one may conclude that release rate depends
for the most part on such parameters as cement surface smoothness,
porosity and wettability. These cements can be also modified with
substances improving drug release rate [14]. Results of the abovementio[...]
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Optimization of Fe and Al elemental powders sintering parameters by DTA analysis
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Stanisław Jóźwiak Krzysztof Karczewski Zbigniew Bojar
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Sintered iron aluminides are very promising novel structural materials
mainly because of their attractive physical and mechanical
properties, but also because of the low price of raw materials used
for their manufacture [1]. Powder metallurgy (PM) eliminates many
of the limitations during the fabrication process [2]. For example,
PM enables forming of products with complex shape, choosing almost
arbitrary chemical compositions, deals with problem of grain
overgrowth, gives better chemical and structure homogeneity as
well it is an energy-saving process [3÷5].
However, in case of the Fe-Al phases, the use of this method is
limited by the necessity of controlling of the SHS (self-propagating
high-temperature synthesis) reaction [3]. SHS occurring during sintering
of Fe and Al elemental powders mixture is very rapid and
strongly exothermic, which unfortunately may cause unwanted porosity
of the sinters [6]. Our previous studies [7÷10] show the great
complexity of phenomena taking place during presintering process
of Fe and Al powders. These effects correlated with diffusion and
phase transformations were also studied by other researchers [1,
3, 4]. It was concluded that the mechanism of exothermic phase
transformations is strongly correlated with many factors, such as
chemical composition of the sample, elemental powder particles
size, atmosphere, and the heating rate. It is important that only the
formation of the exothermic Fe2Al5 phase was reported prior to the
formation of finally-wanted FeAl phase [1].
Our last investigations show however that not only Fe2Al5 but
also other high aluminum phases - FeAl3 and FeAl2 could be found
in the samples structure sintered at temperature lower than the SHS
reaction temperature. In order to limit unfavorable influence of the
SHS on sinter structure, the optimization of the powders particles
size, the compact pressure and the heating rate was done in this
work.
EXPERIMENTAL
Investigation[...]
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Optimization of galvanic bath and operating parameters for amorphous Ni-W electrodeposition
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PAULINA INDYKA EWA BELTOWSKA-LEHMAN AGNIESZKA BIGOS Leszek Tarkowski Marcin Kot JERZY MORGIEL
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Functional coatings obtained by electrodeposition are widely applied
commercially to provide enhanced surface performance for
engineering applications [1]. In recent years much effort has been
put into searching for alternatives to electroplated hard chromium,
the properties of which are often used as a standard for other functional
coatings [2]. Usually, high hardness, wear and corrosion
resistance are the critical properties. Despite the excellent properties
of the hard chromium coatings, used in automotive and aviation
industries, they should be eliminated from the manufacturing
process (according to the EU directives), due to high toxicity and
carcinogenity of hexavalent chromium. Up to now, only electroless
hard Ni and Ni-P coatings have found use in selected applications
[3]. Electrodeposited Ni-based alloys containing refractory metal
(molybdenum or tungsten) could be an important alternative to hard
chromium.
Ni-W alloys are known for their excellent mechanical and tribological
characteristics, but they are very difficult to obtain by
conventional metallothermic methods, due to the large differences
in melting points (Ni - 1455°C, W - 3410°C) as well as limited mutual
solubility of both metals [4]. Hence, electrochemical deposition
can be proposed as an alternative technique. Electrodeposition, as
a cheap, low temperature and simple method, is a superior technique
for manufacture of Ni-W coatings. However, compact and
well adherent to the substrate Ni-W coatings are still electrodeposited
with technical difficulties.
Although tungsten cannot be separately electrodeposited from
aqueous electrolytes, it can be easy co-deposited with iron-group
metals such as nickel to form an alloy [5]. However, the presence
of appropriate complexing agents is necessary. This phenomena is
classified by Brenner as induced co-deposition [6]. Among many
galvanic baths proposed for the Ni-W alloys electroplating (such as
sulfamate, pyrophos[...]
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Oxidation and creep behaviour of the CVD aluminized Rene 77 nickel-based superalloy
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WALDE MARZIAJA Marek PORĘBA JAN SIENIAWSKI
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Turbine blades are heavy loaded elements of the aircraft gas turbines.
They are subjected to extremely high mechanical and thermal
loads in the chemically aggressive environment. The most important
criteria for selection of the blades material are high tensile
strength at elevated temperature both for static and dynamic loads,
high fatigue and creep strength along with good resistance to high
temperature corrosion [1, 2]. Required high temperature oxidation
resistance of the modern gas turbine elements can be obtained by
application of protective coatings. The most effective and widely
used are diffusion coatings containing aluminium: Al-Si, Al-Cr,
Al-Pt, Pt‑AlCr and others [3÷6].
Widely accepted techniques of obtaining coatings based on intermetallic
phases of the Ni-Al system are pack cementation and out
of pack methods. Although they fulfil technological requirements
for manufacturing of aircraft engines elements, they present threat
to environment because of emission of gaseous chlorides during the
process [4].
Aluminizing by chemical vapour deposition method, in which
reactive atmosphere is generated in external reactor and supplied in
the form of aluminium halides into the main reactor, was introduced
successfully to produce heat-resisting diffusion layers of the analogous
chemical and phase composition like in traditional methods [4,
7]. This method allows to avoid contact between substrate material
and powder mixture and provides more precise control of process
parameters. The highest chemical cleanness of the coating obtained
by low-activity CVD process additionally increases their oxidation
resistance [8, 9].
CVD method allows to form the coating both on the external
surface of the turbine blade and simultaneously on the internal surface
of the cooling channels having small cross-section. Additionally
it enables control of the cooling rate of substrate from process
temperature. It facilitates complex heat trea[...]
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Platelets activation and adhesion on TiN+Ti2N+αTi(N) layer produced in plasma space on Ti6Al4V alloy
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MAŁGORZTA GONSIOR ROMAN KUSTOSZ TOMASZ BOROWSKI MACIEJ OSSOWSKI MAREK SANAK BOGUMIŁ JAKIEŁŁA TADEUSZ WIERZCHOŃ
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The original extracorporeal pulsatile heart support device, called
POLVAD, has been developed in Poland. It was used in over 200 patients
with the longest duration of 1 year. The innovative tilting disc
valve for this device is developing. The valve consists of original
valve ring, free of pivot element crossing the blood stream (Fig. 1).
The valve ring is made of titanium alloy Ti6Al4V type. Titanium
and its’ alloys demonstrate numbers of beneficial properties
in medical applications. They are a subject to study metallosis, they
demonstrate very good biotolerance to tissue habitat, high resistance
to corrosion, and thermodynamical stability in physiological conditions.
The thromobogenicity is one among t he problems, regarding
titanium and its’ alloys applications as the biomaterials.
For that reasons appropriate surface modifying layers of titanium
are developed - to improve material properties for blood contact.
Nowadays, surface engineering techniques are used as base point
for creation a proper chemical composition, structure and physicochemical
status of biomaterial surfaces - to obtain its required
biological properties and functions.
The surface modifications of titanium and its’ alloys influence
surface layer structure and morphology, adhesion and inside layer
residual stress. They influence a total implant stability in live organism
habitat as well as improve biocompatibility. The microstructure,
roughness and thrombogenicity of diffusive titanium nitride layers
on titanium Ti6A14Al alloy are examined in the work - together
with thrombogenicity testing, performing as the material induced
platelets activation and its adhesion to the biomaterial surface.
MATERIAL AND METHODS
The titanium nitride layers were formed at the Surface Engineering
Department of Warsaw University of Technology. Three
diffusive layers: TiN+Ti2N+αTi(N), TiO2+Ti2N+αTi(N), and
Ti(OCN[...]
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Porous Fe-Al intermetallics fabricated by SHS reaction in volume control environmental reactor
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KRZYSZT OF KARCZEWSKI STA NIS ŁAW JÓŹWIAK MICHA Ł CHOJNACKI ZBIGNIEW BOJAR
|
Recently, there has been a considerable increase in interest for porous
materials due to their unique properties such as high energy absorbing
capacity, reduced thermal conductivity, enhanced acoustic
damping ability and so forth.
Currently, a great deal of attention is focused on metallic foams.
However, if metals could be substituted by ceramics, intermetallics
or their composites, such foam materials could be used for applications
in extremely severe environments, such as in thermal barrier
coatings at high-temperatures and filter materials in severe corrosive
environments [1, 2].
Among intermetallics, FeAl have been well studied as structural
materials in the past decades [3÷6]. Due to their sound physical and
mechanical properties, FeAl were expected to replace traditionally
materials in many engineering applications. In addition, FeAl intermetallic
compounds have a relatively low density and low cost.
Nevertheless, the brittle fracture and low ductility of FeAl at ambient
temperatures limit their cold working.
The powder metallurgy processing technique may overcome this
problem. The technology based on powder metallurgy eliminates
a number of limitations in the manufacturing process, allowing for
complicated shapes of the semi-finished or finished products. Furthermore,
the technology enables a wide selection of various compositions,
eliminates a problem of the grain coarsening, inhomogeneity
of chemical composition and structure and, finally, assures
easier control of the process of shaping the structure of material, as
well as reduces the use of raw elements [4, 5].
In t[...]
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Powder production method for thermal spraying of wear-resistant and low-friction coatings
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Piotr Kula Robert Pietrasik Łukasz Kaczmarek Adam Krasiński Konrad Dybowski
|
The universal drive towards developing pro-innovative ecological
technologies has contributed significantly to the development of
recycling technologies and remanufacturing of worn-out machine
components. The application of these technologies can substantially
lower the production costs of new spare parts that would possess
similar or even better operational properties; the latter is the case
where refurbishing is combined with modern surface treatment
technologies [1, 2].
Some components are refurbished using Multiplex technologies
that combine reconstruction of the geometry of the components
with improvement in their operational properties through thermal
and chemical treatment. They are particularly useful for, e.g. low-
-friction gradient layers [3÷6].
An optimum, energy-saving and universal solution for this technology
would be to combine surface reconstruction with simultaneous
addition of low-friction coatings resistant to wear. This would
be feasible through the possibility of thermal spraying [7] using
specially prepared powders that would have such properties as high
hardness, durability and a low friction coefficient. These could include
coatings based on, for example, thermochemically hardened
powders conta[...]
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Producing and properties of the polylactide-alumina nanocomposite fibres
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PATRYCJA CZARNEC KA TOMASZ CIAC H ANTONI KUNICKI ANDRZE J OLSZYNA MONIKA GOŁASZEWSKA AGNIESZ KA JASTRZĘBSKA
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Electro-spinning is a very promising and very interesting process
of fibre production. This technique allows us to produce fibres of
a diameter ranging from few na nometers to 1 mm [1÷5].
Experiments have showed that almost every polymer can be
made into fibres by electro-spinning. Electro-spun fibre can be applied
in an aerosol filtration but it can also be used as a drug carrier
or bandage.
First publications about electro-spinning for fibre production
were published by Petrianov [6]. Other current applications include
medical applications of electro-spun fibres as wound dressings.
A portable device for fibres electro-spinning can be applied directly
on the wound and produce a permeable wound dressing, applicable
especially in the case of vast burns [7].
Electro-spun fibres, even if they are very fine, can be easily collected,
if compared to other methods. The method for electro-spinning
fibres collection is showed in Figure 1.
Polylactide (PLA) is polyester produced in the lactide ring-opening
polymerization process. Polylactide is the most important plastic
material that can be derived from renewable resources. It also
has an omnipresent status in the biomedical field, because of ability
to decompose over a period of time [8].
In case of materials that can be decomposed in human organism,
it is crucial to use filler, which will serve as a scaffold for human
tissue after polylactide decomposition.
Among all inert inorganic fill[...]
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Properties of high alloyed CrMnNi steels with strain induced α′ martensite formation
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Andreas Jahn Alexander Kovalev Steffen Wolf Andreas WeiSS Lutz Krüger Piotr R. Scheller
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It is well known that austenitic chromium-nickel or chromium-manganese-
nickel steels with low stacking fault energy show a stress
and strain induced formation of martensite during mechanical loading.
The transformation induced plasticity (TRIP) effect occurs in
metastable austenitic or austenitic-martensitic steels for wrought
and also cast alloys [1]. The strain induced formation of martensite
is controlled as well by its chemical composition as by stresses [2],
which are higher than the yield stress of the initial microstructure.
They activate shear processes accompanied by deformations. For
each type of strain induced martensite formation a triggering stress
exists which is controlled by the temperature and the chemical composition
of the steel. This can be obtained from suitable experiments
[3÷5]. Generally three mechanisms of the martensite formation,
the γ→ε, ε→α′ and γ→α′ transformation, are discussed in Cr-Ni
steels. During the γ→ε transformation the ε phase is observed as
thin straight lines in the microstructure of the austenite [6]. The γ→ε
and ε→α′ transformation can proceed simultaneously. The result is
the γ→ε→α′ sequence [3÷4]. During this process the ε martensite
is an instable intermediate phase and usually cannot be detected. In
Cr-Mn-Ni steels the ε martensite is an intensively discussed subject.
It is open either the ε martensite is a unique phase or a pseudo-phase
caused by the concentration of stacking faults in the direction of
load. The reasons for these plastic deformations are the commonly
observed phenomena as shearing strain, twinning and different slip
processes in the initial phase. Thus, some of these mechanisms are
linked to special movements of dislocations. The strain induced formation
of martensite generates the TRIP effect. It is [...]
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Quantitative evaluation of γʹ phase in CMSX-4 superalloy
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AGNIESZKA SZCZOTOK TOMASZ RZYCHOŃ JAN CWAJNA
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The microstructure of nickel-base superalloys determines their mechanical
behaviour. The strength of Ni-base superalloys is dependent
on such factors as volume fraction, size, coarsening rate, and
composition of γʹ phase precipitates [1].
The content and size of γʹ phase precipitates embedded in a cubic
face-centred γ matrix can be adjusted by the alloy design and heat
treatments. The composition of the ordered γʹ precipitates does differ,
i.e. Ni3(Al, Ti, ...), and depends on the alloy composition and
processing [2].
The characterization of γʹ phase precipitates in different nickelbased
superalloys has been the subject of extensive research work.
Volume fraction of the γʹ phase in Ni-base superalloys is a significant
element influencing on working out the superalloys chemical
compositions [3].
MATERIAL
The measurements of γʹ phase precipitations were carried out on a
monocrystalline cylindrical bar of 8 mm diameter made of CMSX-4
nickel-base superalloy [4]. The bar was cast in Laboratory of Material
Research for Aircraft Industry in Rzeszów.
The material was investigated in the as-cast condition.
IMAGE ACQUISITION AND ANALYSIS
OF γʹ PHASE PRECIPITATES
The bar intended for investigations was cut perpendicularly to the
main axis. The procedure of metallographic specimen preparation
was described in details in Table 1.
Quantitative metallography of CMSX-4 requires the revealing
of γʹ precipitates by means of an appropriate etching conditions selection
as well as use of appropriate image acquisition in order to
observe the γʹ precipitates and register the images of the superalloy
microstructure with them.
In the previous work two etching methods of the γʹ phase precipitates
were described [5]. For a quantitative evaluation of the
precipitates etchant caused their etching and leaving the γ matrix is
better, so in the ca[...]
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Real kinetics of Fe-Al type intermetallic phases sintering analysis based on extended JMA model
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MICHAŁ CHOJNACKI STANISŁAW JÓŹWIAK KRZYSZTOF KARCZEWSKI ZBIGNIEW BOJAR
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Production of certain advanced ceramics, composites, and intermetallic
compounds in most cases is connected with complex and high
energy consumption techniques. Increasing tendency to limit costs
of fabrication requires development of efficient and energy-saving
technologies. In case of Fe-Al intermetallic materials fabrication
Powder Metallurgy (PM) methods associated by Self-propagating
High-temperature Synthesis (SHS) become more popular [1].
Nevertheless, SHS assisted sintering is connected with high intensity,
high synthesis temperature and limited possibilities of reaction
control which lead to high porosity of sinters [2]. Such issues
require deep study of intermetallic phases nucleation and transformation
mechanisms during SHS reaction.
Kinetic parameter of those transformations, for example the
Avrami exponent n, could be calculated from DSC experiments
according to the JMA model adapted to non-isothermal conditions
[3÷12]. Unfortunately the JMA equation which allows to determine
nucleation and growth mechanism on the basis of Avrami exponent
n value has some limitations [13]. In theory Avrami plot should be
a straight line of which slope is the Avrami exponent n. The experimentally
observed kinetics show some deviations from this theory.
They are connected with continuously changing reaction conditions
forcing to calculate the slope of straight linear fragment of such plot
in range from about 25 to about 75% of degree of phase transformation
α. Thereby calculated value of n is affected by some error
and does not give any insight in phase formation mechanism at the
beginning and the final stage of the process. Some authors suggest
that in order to eliminate this inaccuracy the local Avrami exponent
should be calculated [14]. The aim of this study was to compute the
local Avrami exponent n(T) from slope of lines parallel to tangent to
Avrami plot lines in following points from entire range of particular
phase form[...]
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Research on the texture of Cu/Ni multilayers with a diversified period thickness
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Barbara Kucharska Edyta Kulej Małgorzata Witkowska Zygmunt Nitkiewicz
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The modification of materials surface, including the production of
surface layers and coatings, constitutes now one of the key problems
of materials engineering. Particularly interesting is the production of
coatings in a multilayer system, whereby materials of unique properties
resulting from the diversified composition of components (such as
metals, semiconductors, and their combinations) can be obtained [1].
From the point of view of magnetic properties, multilayers in
ferromagnetic/diamagnetic material systems are being intensively
investigated, owing to the gigantic magnetoresistance (GMR) phenomenon
that has been discovered in them by a team of scientists under
the guidance of Alberta Fert and Peter Grünberg. A thin-layered
Cu/Ni structure is a classical example of a multilayer of such properties,
which could be applied in construction of hard discs [2÷7].
The identical crystallographic structure, fcc, and the very small misfit
(2.5%) of the copper and nickel lattices cause Cu/Ni multilayers
to exhibit good mutual adhesion and to be easily made by various
techniques, including PVD [8, 9].
Depending on their production technique and thickness, multilayers
can exhibit a different degree of texturing. A heavy texturing
of sublayers causes an increase in the roughness of interfacial
surfaces, which adversely affects the quality of the multilayers, e.g.
impairs their magnetic properties [10, 11]. For the examination of
the structure and quality of coatings, the X-ray diffraction technique
is commonly used [12÷14].
Material and methodology
The material used for tests were Cu/Ni multilayers produced on
a monocrystalline Si(100) silicon substrate by the magnetron sputtering
method. The multilayers were diversified in terms of Ni sublayer
thickness (1, 3 and 6 nm), while maintaining a fixed Cu sublayer
thickness of 2 nm. Each multilayer was built of 100 periods,
each of a thickness[...]
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Resistance to isothermal oxidation of austenitic cast steel with Ti addition
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MAŁGORZATA GARBIAK RENATA CHYLIŃSKA BOGDAN PIEKARSKI
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Highly alloyed nickel-chromium cast steels form a group of structural
materials that ensure durability of components at elevated and
high temperatures in a corrosive environment. The durability of
these alloys is owed to their good mechanical properties and excellent
chemical stability [1].
Most of the working environments that these alloys are subjected
to contain oxygen, carbon dioxide and water vapours. The
good corrosion resistance of these alloys is attributed to the ability
to form continuous, dense layer of oxides on the surface of the material,
which consists mainly of Cr2O3 [2, 3]. Such layers act also as
protective coatings in carburising atmospheres [4].
Apart from required level of chromium the protective effectiveness
of such oxide layers is strongly influenced by addition of other
alloying elements such as Si, elements of the group III and IV of the
periodic table (e.g. Nb, Ti, Zr) or rare earth elements (Ce, Nd, Pr).
These may be introduced to the alloy individually or as a mixture
adding up from tenth parts to several percents [1÷3, 5].
The aim of this work is to describe the influence of Ti additions
in 30Ni-18Cr alloys on resistance to isothermic oxidation in air at
900°C temperature.
Titanium belongs to the group of elements with high affinity to
oxygen. The oxides of titanium are stable in a wide range of temperatures.
Although the role of titanium on oxidation resistance
improvement of austenitic alloys is not established in undeniable
manner [6] it is nonetheless recommended for alloys working in oxidising
atmospheres. However, due to difficulties with introduction
of Ti to these alloys in the melting process and related castability
deterioration in practice addition of niobium is preferred [1, 7, 8].
EXPERIMENTAL
Two sets of specimens from 30Ni-18Cr creep resistant cast steel
were prepared with two levels of Ti (Tab. 1) using sand gravity casting.
The materials preparation, melting and casting process w[...]
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Rheological behavior of nanosized silica suspensions
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Tomasz Żmigrodzki Anna Danelska Łukasz Wierzbicki Marcin Leonowicz Mikołaj Szafra n
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Most materials behave in such a way that they have a combination
of viscous and elastic response under stress or deformation. Materials
behave in linear manner, as described by Hooke or Newton, on
in a small scale. Among real liquids the Newtonian and non-Newtonian
fluids can be distinguished. Viscosity is one of the rheological
parameters which can characterize the liquids. By measurements
of the viscosity versus share rate one can classify the liquid into
a particular group. If the viscosity is decreasing vs. shear rate the
liquid has shear thinning properties, when the viscosity is rapidly
increasing the shear thickening effect or dilatancy is observed. The
rheological classification of liquids is presented in Figure 1 [1].
Shear thickening effect appears in suspensions having various
concentration and morphology of solid phase. The shear thickening
of fluids can be explained by a few theories. The most popular is
the clustering theory. According to its main assumption the particles,
at low shear rates, are prevented from aggregation by steric
repulsive and Brownian forces. Under increasing shear rate the
hydrodynamic forces also increase and the particles form chains,
blocking the flow of the fluid. The next potential explanation of the
dilatancy phenomenon, is Order-Disorder Transition (ODT) theory,
which claims that t[...]
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Selection of heat treatment and aluminizing sequence for Rene 77 superalloy
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MAREK PORĘBA JAN SIENIAWSKI
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One of the key issues of modern aerospace industry is protection
of the hot part of the aircraft engine against oxidation and corrosive
atmosphere. Development of the engines is related not only to
growing efficiency but also to operational reliability of the components
critical for flight safety. Nickel-base alloys have been used for
blades in gas turbines since early 50s of XX century [1, 2]. Extension
of the service life of turbine blades and their reliability is possible
through increase of heat and creep resistance of the material.
Creep resistance can be controlled by proper heat treatment whereas
heat resistance can be raised by protective coatings application. One
of the possible solutions is deposition of diffusion coating based on
nickel aluminides in the process of aluminizing [3, 4].
Advantageous properties of aluminium result from its high affinity
to oxygen. Production of aluminides coatings containing intermetallic
phases of the Ni-Al system is most often realized by pack
cementation and chemical vapour deposition (CVD). Among the
various phases of the Ni-Al system like γʹ-Ni3Al, β-NiAl, δ-Ni2Al3
and ε-NiAl3, the primary phase of the coatings obtained in the aluminizing
process of nickel-base superalloys is β-NiAl. Specific
physicochemical properties of that phase are high heat resistance,
heat conductivity and density which is smaller comparing to the
nickel-base alloys [4÷6].
Aluminizing by CVD method enables simultaneous forming of
the coating both on the external surface of the turbine blade and on
the internal surface of the cooling channels, allows to control the
cooling rate of substrate and to combine it with heat treatment of the
cast nickel-base superalloys [7÷9].
The aim of the study was to determine the effect of the parameters
of thermochemical treatment of Rene 77 superalloy (precipitation
hardening and aluminizing) on its oxidation resistance and
creep properties.
ma[...]
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Self-lubricanting cold forging tools
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Hanna Wiśniewska-Weinert Jacek Borowski Mikhail Ignatev BOHUMIL Jedovnicky Tomasz RY BAK Volf Leshchynsky
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In recent years, larger, more complex parts have been successfully
cold forged due to improvements in forming equipment, die and
workpiece materials, die coatings, and process design. In addition
to the savings in energy costs, modern cold forging enables parts to
be produced to near net shape [1].
Working conditions of forging tools have become severer with
the years and it has been required for forging tools used to this end
to increase the hardness, wear resistance and heat resistance. A typical
shape of the tools exhibits an assembling in which a Cemented
Carbides (CC) or High Speed Steel Insert (HSS) mounted into the
casing. In these CC and HSS tools, the surface of the insert is ordinarily
coated by CVD/PVD methods [2].
Many factors influence component accuracy in the form of
systematic and random dimensional errors in the cold forming
processes. There are four important factors that affect the component
systematic errors, i.e.: imperfection of the material plastic flow,
elastic deformation of the press system, elastic–plastic deformation
and thermal behaviour of the tools and component [3]. The later two
factors are most important and relevant to process and tool design
of formed components. These effects become evident during different
stages in the cold forming process, typically including forming,
unloading, ejection and cooling. The repetitive production cycles
in the industrial practice will bring further issues of dimensional
changes due to tool wear and temperature increase developed over
time. Thus, the tool wear resistance is one of the most important
requirements.[...]
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Shape recovery characteristic of ferrous shape memory alloy by prestrain of biaxial stress
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Hisashi NAOI TAKAMASA GAMOU TAIKI KAWAGUchI MANABU WADA TADAKATSU MAruyama
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As for the ferrous shape memory alloy, the application to the connection
components including the tube fittings [1] and the large-
-scale structural material with the functionality is expected. In order
to apply this alloy to the connecting materials, it is necessary
to estimate the amount of deformation and the connecting strength
after prestrain is supplied and shape recovery heat-treatment is performed.
Because the forming method of the prestrain is often given not
only uniaxially but also multiaxially, the investigation of the shape
recovery characteristic to the multiaxial forming is important for
wide practical use of the alloy. Authors investigated [4, 8, 9] the
shape recovery characteristic concerning the prestrain formed during
the uniaxial stretching of tensile test and the biaxial stretching
of the hydraulic pressure bulge forming. In addition, the consideration
based on the mechanism of the stress-induced martensitic
transformation that rules the shape recovery behavior has been studied.
However, a wide-ranging investigation has been requested as
for the data of the shape recovery strain of the transitional region
from the uniaxial stretching to the biaxial stress condition because
the shape recovery data are not sufficient. Figure 1 shows the schematic
of stress-strain and temperature-strain curve in the shape recovery
process.
The strain worked by plastic deformation to the specimen in this
report is defined as εp of prestrain, and the strain measured by the
displacement of the gauge length from before to after the heat treatment
is defined as εr of shape recovery strain. When the alloy is
applied to a fixed amount of deformation and is heated at a fixed
temperature repeatedly, larger shape recovery strain will be developed.
This phenomenon is called training effect.
It is reported [4] that the shape recovery strains of Fe-28%Mn-
6%Si-5%Cr alloy are measured in the case of without training and
with trai[...]
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Structural and mechanical properties of Al-0.25Zr alloy obtained on the way of RS ribbons consolidation
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Tomasz Tokarski
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During the last decade, an extensive research programmes on development
of new materials that are capable to meet a constantly
rising industry demands were run. Nanotechnology and grain size
refinement techniques generated new possibilities in the fields of
materials construction. Those novel procedures can be applied to
design new products that could meet contradictory requirements,
for example material for energy transmission lines. Such materials
should be characterized by as high as possible electrical conductivity
and specific strength, stable at elevated temperatures [1]. There is
always a contradiction between the two, since usually an improvement
of one parameter results in decrease of the other.
First generation power lines were constructed from aluminum
cables reinforced with steel strands. Aluminum has lower electrical
conductivity than copper but it is more than compensated by lower
density and cost. A direction of further development was to increase
the ampacity (current carrying capability). Second generation, self
supporting cables, was devoid of steel core. The required strength
in order to be able to self support was obtained by addition of alloying
elements to aluminum.
Mechanical properties were effectively enhanced by solid solution
strengthening or precipitation strengthening. Usage of these
conventional strengthening mechanisms results in degradation of
electrical conductivity as a consequence of the presence of alloying
elements in the solute form in the matrix. Total ampacity change
is positive due to elimination of steel core and increase of crosssection
utilization for carrying the current. Investigations are carried
out in order to enhance conductivity while keeping mechanical
properties at the highest possible level.
In order to meet these requirements, usage of a completely different
strengthening mechanism is proposed. It is well known that
materials strength increase can be obtained by refinement[...]
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Structural and physical properties of chromium layers obtained by pulse plating techniques
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Naroa Imaz EVA GARCÍA-LECINA José Antonio Díez Miren OSTRA MarIa SARRET
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Chromium plating has successfully been used since 1925, representing
one of the most important processes in the galvanic industry
due to its unique combination of wear, hardness and corrosion
properties at low cost. Chromium electrodeposition is widely used
in automotive, aerospace, industrial and general engineering applications
for both decorative and functional coatings [1, 2]. Two types
of chromium coatings can be classified according to their thickness:
decorative chromium (0.80 μm) and functional or hard chromium
(20÷500 μm).
The most common hard chromium electrolyte is constituted by
chromium oxide solutions containing a low concentration of one
or more catalysts, usually sulphate. The current efficiency of chromium
electrodeposition is low, using only 10÷15% of the applied
current: the majority of the electric charge is consumed by the hydrogen
evolution reaction (80÷90%) and 5% of the current is used
in the reduction of hexavalent chromium to trivalent chromium species.
However, and in spite of its low current efficiency and the
carcinogenity and toxicity of hexavalent chromium, this process is
not currently replaceable due to the excellent properties of the coatings
obtained [3].
A key factor to modify the properties of a coating is to focus on
its microstructure. Thus, it is well known that there is a relationship
between the processing parameters and the microstructure, morphology
and properties of the coatings.
Different approaches can be undertaken to modify the microstructure
of a coating. In this sense, pulse plating techniques are
widely used in the electrodeposition of metals and alloys due to
their reported influence into metallic distribution, efficiency, microstructure,
morphology and coating properties [4÷6]. In pulse plating
the current is interrupted or alternated on a short time scale during
the metal electrodeposition, offering a higher number of variables
comparing to direct current proces[...]
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Structure and properties of Al-Cu-Fe thin films deposited by PLD technique
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SŁAWOMIR KĄC MAŁGORZATA KĄC
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Recent progress in the development of quasicrystals (QCs) as low-
-friction, hard materials, makes these alloys ideal candidates for
protective coatings. However one disadvantage of quasicrystals is
that they are quite brittle. To overcome this problem, we are taking
advantage of nonstructural materials and produce coatings, which
consist of a nanograin quasicrystals and metal.
Quasicrystals are alloys, which have long-range rotational symmetry,
but lack translational periodicity in three dimensions. In spite
of the lack of translational periodicity, these materials show sharp
diffraction patterns with symmetries, which are forbidden for ordinary
crystals (five-fold or ten-fold axes, for instance) [1]. Analysis
of bibliography [2÷4] shows that quasicrystals exhibit intriguing
surface properties in air.
First of all, they have low coefficient of friction, low propensity
to wetting by polar liquids, excellent oxidation resistance and high
hardness. However, given that they are brittle materials they are
usually employed as film coatings.
Up to now, quasicrystalline phases have been observed in over
100 different metal alloy systems. One of the systems creating of
quasicrystal phases are Al-Cu-Fe alloys. Their friction properties
and hardness makes them an interesting material for wear-resistant
coatings. Their low thermal conductivity and their improved ductility
above 750°C make them suitable for thermal barrier coatings
[2, 5, 7].
The production of good quality quasicrystalline Al-Cu-Fe alloys
on an industrial scale is still difficult. Literature study shows, that
is possible to form Al-Cu-Fe quasicrystals using different methods,
like melting and solidification, melt spinning, gas atomization, mechanical
alloying [2], and by PLD technique [4, 6, 8].
Literature study [9, 10] indicates that PLD technique which allows
to transform stoichiometrically material from the target to
film seems to be an ideal method for preparation of[...]
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Structure and properties of low temperature nitrided/oxidized NiTi alloy
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Józef Lelątko Tomasz Goryczka Tadeusz Wierzchoń Maciej Ossowski Bożena Łosiewicz
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NiTi alloys have been widely used in biomedical field due to their
shape memory effect, superelasticity and good biocompatibility [1].
They are excellent biomaterials for orthopaedics, dental applications,
vascular and organ surgeries. However, these applications,
especially as a long term implants, require special attention with respect
to nickel ion release into the patient’s metabolism system and
the surrounding tissue. The nickel can cause allergies if persons are
highly sensitive and has a toxic effect on the cell when its concentration
exceeds a certain level [2]. In order to improve the corrosion
resistance of the NiTi alloy and suppress the release of nickel ions,
many surface modification techniques have been used. Titanium
oxide and nitride has been found a good candidate for layers, which
sufficiently protect human body [3, 4]. Additionally, combination
of a layer sequence, forming the titanium oxide and titanium nitride
layers, increases corrosion resistance and biocompatibility [5].
The titanium oxide, especially TiO2 [6], increases the stability of the
surface, creates the physical and chemical barrier against oxygen
migration to the top and limits the way of the nickel oxidation [7].
Low chemical reactivity, high hardness as well as wear and corrosion
resistance are characteristic properties of the titanium nitride
and titanium oxide layers. Reported results show that layers were
thick. Moreover, between the layer and the NiTi matrix a sublayer
of intermetallic phases such as Ni3Ti or Ti2Ni were formed [5, 8].
All phases reveal low plastic properties, which limit their practical
application in the field of medicine where the shape memory effect
or superelasticity is required. Therefore, the formation of very thin
surface layers of TiN, TiO2 or TiN+TiO2 with suitable nanostructure
is the way to improve the biocompatibility of NiTi alloy with shape
memory effect.
In the present work the thin nitride-oxide lay[...]
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Structure of sintered Ni-Ti-Fe shape memory alloys
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Tomasz Goryczka Barbara Szaraniec Józe Flelątko
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Properties of NiTi shape memory alloy (SMA) are sensitive to any
modification that can change the atom environment. It is due to the
occurrence of the reversible thermoelastic martensitic transformation.
This transformation is so called “civil" transition and proceeds
by a correlated atom shuffle. Among the known modifications of NiTi
properties there are changes in the chemical composition [1], thermomechanical
treatment [2] and/or manufacturing technique [3].
First of all, the NiTi alloys are sensitive to changes in chemical
composition. The raise of titanium contents of 0.1 at. % increases
the transformation temperatures of 10 degrees. Moreover, substitution
of either nickel or titanium by third alloying element strongly
influences thermal behavior. The third element can be use for
controlling transformation temperatures, thermal hysteresis width,
change of the transformation course and sequences as well as for
increase the stability of the transformation temperatures [4]. For example
addition of zirconium or hafnium increases transformation
temperatures [5], whereas cobalt, iron or aluminum decreases of
their values [6]. Copper reduces [7] while hafnium [5] broadens
thermal hysteresis of the martensitic transformation.
In comparison to a binary NiTi alloy, addition of iron or cobalt
causes change in the course of the martensitic transformation. In
the NiTi alloy the B2 parent phase transforms directly to the B19´
monoclinic martensite. In ternary NiTiFe or NiTiCo alloy this transformation
is preceded by additional phase transition - the R-phase
transformation [8]. It is worth to note that the B2-R-B19´ transformation
sequence can occur without any special thermal or thermo-
-mechanical treatment.
In order to directly influence the martensitic transformation the
nonconventional production techniques such as powder metallurgy
(PM) [9], melt-spinning (MS) [9] or twin roll casting (TRC) [10] for
manufacturing the NiTi-ba[...]
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Structure, thermal and magnetic properties of ferromagnetic Co-Ni-Al alloys
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Wojciech Maziarz Jan dutkiewicz Aleksandra kolano-burian Ritta szymczak
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Ferromagnetic shape memory alloys (FSMAs) are being intensively
studied because of their potential applications as smart materials.
Martensitic transformations and lattice reorientation processes in
FSMAs can be triggered not only by changes in temperature and
stress, as in conventional SMAs, but also by applying an external
magnetic field. The martensitic phase transformation of the ferromagnetic
Co-Ni-Al alloy systems has been studied in several papers
[1÷5]. The Curie and the martensitic transition temperatures of the
β phase increase and decrease with increasing the Co content, respectively.
The shape memory effect proceeds due to the thermoelastic
martensitic transformation from the B2 parent phase into the
martensite phase with L10 structure. The unique properties of the
Co-Ni-Al alloy system is an improved ductility allowing hot rolling
and cold rolling of a presence of γ phase with fcc structure. The β
single-phase polycrystalline alloys show a poor ductility [2]. It has
been reported that the hot fabricability of NiAl-based alloys could
be improved by the introduction of γ phase [6, 7]. Since the composition
range of β phase exhibiting the FSM is located near the β + γ
two-phase region, the β-based alloys are able to introduce the γ phase
by suitable choice of composition and heat treatment temperature
[1, 2]. Several percent of γ phase significantly improves the ductility
of the Co-Ni-Al two-phase alloys, which is of great advantage
for practical applications [8]. Compounds with a strong coupling
between crystallographic structure and magnetism usually exhibit
a magnetic field dependence of the structural transitions. A typical
example is the Gd5(SixGe1-x)4 alloys (0.24 ≤ x ≤ 0.5), where a transformation
from the paramagnetic monoclinic phase to the ferromagnetic
orthorhombic phase can be induced either by cooling or
by the application of a magnetic field [9[...]
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Study of the properties of Al2O3-Ag nanopowders produced by thermal decomposition-reduction method and colloidal nanosilver impregnation
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AGNIESZKA JASTRZ ĘBSKA ANDRZE J OLSZYNA ANTONI KUNICKI
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There is a great need for antimicrobial materials across many industries
and disciplines. That is why silver nanoparticles have been the
centre of great interest in recent years. Owing to their small size,
silver nanoparticles present good chemical activity, which is size
and shape dependent [1]. They also possess good antirheumatic and
antiphlogistic properties.
As well as silver cations, silver nanoparticles affect wide range
Gram-positive, Gram-negative bacteria and fungi [2]. Furthermore,
it is unlikely that microorganisms will acquire resistance toward silver
nanoparticles, compared to other biocides like antibiotics [3]. As
a result, the potential for nanosilver-doped materials is limitless.
Silver nanoparticles have been investigated as an addition to
various types of matrices, due to their antimicrobial properties.
Currently most important applications in the medical field include:
wound dressings [4], medical implant coatings [5], ultrafiltration
membranes and antifouling materials [6].
Although such “free" nanoparticles are not suitable in most applications
(e.g. wound dressings) because they can be subsequently
removed from the material while using it. In case of those materials,
it is crucial to incorporate silver nanoparticles permanently.
However, this problem can be solved by using a support. Among all
inert supports, alumina is the most promising one. For silver nanoparticles
incorporation, only alumina porous sinters [7], spheres [8]
or needles [4] have been applied. Owing to alumina nanoparticles
small size, which is no greater than 100 nm, they present large surface
area. They are also characterized as the most inert ceramic for
human organism, which have a good biocompatibility [5]. Due to
these properties, alumina nanoparticles can be used as a support for
silver nanoparticles.
OBTAINING ALUMINA -SIL VER
NANO PARTICLES
For the synthesis of nanosilver particles (20 nm) supported on the
alumina nanop[...]
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Surface modification of titanium subjected to hydrostatic extrusion
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Krz ysztof Topolski Halina Garbacz Wacław Pachla Krzysztof J. KurzydLowski
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The basic technology for producing large volumes of bulk nanocrystalline
metals is based on the Severe Plastic Deformation (SPD)
methods, which enable refining the structure from the micrometric
to the nanometric level. The microstructural changes are accompanied
by a significant improvement of the mechanical strength and
hardness [1÷7]. One of the SPD methods is hydrostatic extrusion,
employed in the present experiments, which has been proven to
efficiently refine the grains in aluminum, copper, nickel and steel
[8÷12].
Our earlier studies have shown that hydroextrusion can also be
used for producing nanostructured titanium [13÷15] with an equivalent
diameter of grains about 60 nm and substantially increased
strength and hardness.
The chief difficulty in producing nanocrystalline titanium by
HE is that the reduction of the rod cross-section must be realized
gradually in many passes. Other disadvantageous effects that occur
during HE of Ti are: the high extrusion pressure, the recurrent
elastic deformation, the stick slip effect (stepwise displacement of
the material) and a considerable wear of the die resulting from the
tribological conditions.
The aim of the study was to reduce or eliminate these adverse
effects, and thereby to optimize the hydroextrusion process of titanium.
To this end the surface of titanium was subjected to various
modifications. The beneficial effect of Ti-Al coatings was shown in
our earlier publications [15, 16]. Even though the extrusion pressure
was reduced, the Ti-Al layers underwent wear in a short time.
In the present study, the Ti billets were covered with Al coatings
of various thicknesses. The effect of these coatings on hydroextrusion
process, the surface topography of the Ti products and their
microstructure after the extrusion were investigated. The maximum
strain was also determined that could be applied in a single and two
extrusion passes.
MATERIALs AND PROCESSING
The material examine[...]
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Synthesis and properties of hot-pressed Ti-Al-C-N materials
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Leszek Chlubny Jerzy Lis Mirosław m. Bućk o
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Among many covalent materials such as carbides or nitrides there
is a group of ternary compounds referred in literature as H-phases,
Hägg-phases, Novotny-phases or thermodynamically stable
nanolaminates. These compounds have a Mn+1AXn stoichiometry,
where M is an early transition metal, A is an element of A groups
(mostly IIIA or IVA) and X is carbon and/or nitrogen. Heterodesmic
structures of these phases are hexagonal, P63/mmc, and specifically
layered. They consist of alternate near close-packed layers of M6X
octahedrons with strong covalent bonds and layers of A atoms located
at the centre of trigonal prisms. The M6X octahedra, similar
to those forming respective binary carbides, are connected one to
another by shared edges. Variability of chemical composition of the
nanolaminates is usually labelled by the symbol describing their stoichiometry,
e.g. Ti2AlN represents 211 type phase and Ti3AlC2 - 312
typ. Structurally, differences between the respective phases consist
in the number of M layers separating the A layers: in the 211’s there
are two whereas in the 321’s three M layers [1÷3]. The layered,
heterodesmic structure of MAX phases led to an extraordinary set
of properties. These materials combine properties of ceramics like
high stiffness, moderately low coefficient of thermal expansion and
excellent thermal and chemical resistance with low hardness, good
compressive strength, high fracture toughness, ductile behavior,
good electrical and thermal conductivity characteristic for metals.
They can be used to produce ceramic armor based on functionally
graded materials (FGM) or as a matrix in ceramic-based composites
reinforced by covalent phases [4].
This work was focused on synthesis of three materials in
Ti-Al-C-N system, namely Ti3AlC2, Ti2AlN, Ti3Al(C, N)2, by the
Self-propagating High-temperature Synthesis (SHS), than obtained
powders were hot-pressed and some of their properties were examined.
PREPARATI[...]
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Synthesis and properties of magnetorheological fluids
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JOANNA KOZŁOWSKA MARCIN LEONOWICZ
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Magnetorheological fluids (MRFs) belong to a group of smart materials,
which have the ability of “intelligent" response to external
stimuli. In the case of MRFs external factor is magnetic field.
MRFs contain micrometric size magnetic particles, randomly
distributed in non-magnetic liquid, which usually is synthetic or
natural oil, water etc. The change of rheological parameters under
magnetic field is called magnetorheological effect.
MRFs were discovered by Jacob Rainbow in 1948 y. However,
more extended interest in MRFs occurred at the end of XX century,
when advantages of their potential application were noticed. The
considerable interested in MRFs arise from their unique ability of
rapid and reversible changes of rheological properties. Applications
of MRFs include actuators, shock absorbers, dampers, brakes and
clutches [3÷6].
MRFs are composite materials that basically consist of three
components:
-- filler material - magnetically polarizable particles, which provide
the magnetorheological effect,
-- carrier fluid, having a function of dispersing medium,
-- stabilizer - protecting the particles from agglomeration.
Factors that influence properties of MRFs can be classified into
two groups:
1. Extrinsic factors:
-- strength of magnetic field,
-- shear rate,
-- temperature.
2. Intrinsic factors:
-- type of magnetic particles, their saturation magnetization and
coercive force,
-- size of magnetic particles and particle size distribution,
-- volume (mass) fraction of components,
-- carrier liquid type, its viscosity and thermal stability,
-- stabilizer type.
In order to increase the yield stress capability it is necessary
to have a higher percentage of metal powder to support the chain
structure in a magnetic field [1].
The saturation magnetization of the particles should be high
enough to achieve strong magnetorheological effect. Moreover, low
coercivity of the magnetic particles is required to ensure reversi[...]
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Synthesis of magnetic nanocrystallites in carbon matrix
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Ewa Szmidt MARCIN LEONOWICZ MARTA IZYDORZAK Elżbieta Jezierska
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Nanoscopic magnetic systems attract substantial scientific attention
due to the unusual properties which differ them from their bulk
counterparts. In the consequence of reduced dimensions increases
overall magnetic anisotropy of the particles, which is accompanied
by decrease of the magnetic moment and Curie temperature. Magnetic
nanostructures exhibit several new phenomena, which do not
occur in bulk magnetics, such as superparamagnetism, magnetic
quantum tunneling, giant magnetoresistance, exchange bias, spin
torque, spin Hall effect and other.
Magnetic nanoparticles can exist as individual nanocrystallites
[1] or be dispersed within beads [2÷7]. Their properties depend on
the size and nature of magnetic interactions. Single domain particles,
below certain critical size, usually 5÷15 nm, may exhibit
superparamagnetic properties, in which remanence and coercivity
goes to zero and saturation magnetization is the same as in the ferromagnetic
ordering. Such nanoparticles do not “stick" together in
the absence of the magnetic field, however, they still agglomerate
tending to reduce the surface energy. Thus, synthesis of magnetic
nanoparticles within larger beads, where they are separated within
a matrix, seems to be a proper solution.
The characteristic magnetic properties of nanostructures predispose
them for various new applications, mostly in electronics
and medicine. Biomedical applications are rapidly growing areas
of applications for nanosystems and comprise magnetic resonance
imaging [8, 9], hyperthermia [10], targeted drug delivery [11÷15],
tagging of biological nanomaterials [16, 17], biological sensors and
several other.
Wide application of magnetic nanosystems is possible due to the
rapid development of fabrication and characterization techniques.
Among the former one can mention vapour deposition, solution
chemistry, elektrophoretic deposition, arc discharge and other.
In this study magnetic nanocrystallites we[...]
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TEM analysis of creep mechanisms of single-crystalline nickel-base superalloys
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Beata Dubiel Aleksandra czyrska-Filemonowicz
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Single crystal (SC) superalloys are especially designed for gas turbine
blades in jet aircraft engines and stationary turbines generating
electricity. The basis criterion in material selection for gas turbine
blades is a high creep strength, because they have to withstand centrifugal
forces acting during operation.
The main creep mechanisms in polycrystalline superalloys are:
-- dislocation creep by combined slip and climb of dislocations,
-- diffusion creep by Nabarro-Herring or Coble mechanism [1, 2].
As it was shown for many superalloys [3÷5], in the range of temperature
and stresses characteristic for service conditions of turbine
blades, grain boundary diffusion by Coble mechanism is the main
factor controlling the creep rate. Therefore the elimination of grain
boundaries is necessary for improvement of creep resistance of
superalloys. It can be achieved by a directional solidification with
a grain selector, as was demonstrated first by B. Piearcey from Pratt
& Whitney in 1970 [6]. Single crystal superalloys exhibit the highest
creep resistance among metallic materials. The development of
chemical composition of SC superalloys resulted in elaboration of
four generations of these alloys [7, 8] and progress continues already
towards the fifths generation [9].
The as-cast single crystal superalloys exhibit a dendritic structure
with the eutectic areas between dendrite arms, which can be
homogenized by heat treatment. The typical microstructure consists
of about 70% of cuboid γʹ precipitates, about 400 nm in size,
separated by γ matrix channels about 30 nm wide. Residual eutectic
areas contain large irregular γʹ precipitates. Such two-phase microstructure
guarantees the high creep resistance of single-crystalline
turbine blades. The γʹ precipitates are an ordered Ni3Al-base intermetallic
phase with the lattice parameter only slightly smaller than
the Ni-base γ solid solution. This produc[...]
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Texturization of polycrystalline silicon by metal assisted chemical etching
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Marek Lipiński
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Cell reflectance is one of the factors influencing the efficiency of
silicon solar cells. Therefore, the reduction of optical losses can significantly
improve the efficiency of the solar cell. At present, the
monocrystalline silicon wafers with (100) crystallographic orientation
are textured by an anisotropic alkaline chemical etching. However,
this method is not suitable for polycrystalline silicon due to
different crystallographic orientations of the crystal grains. On the
other hand, an isotropic acidic texturization based on a HF/HNO3
etching solution gives better results for polycrystalline silicon because
every grain orientation is etched with the same rate. Unfortunately,
isotextured mc-Si solar cells still suffer from high surface reflection.
The new method of texturization is based on metal-assisted
chemical etching (MAE). It was shown that MAE can produce the
black silicon with very low surface reflectivity [1]. It is based on the
deposition of metal clusters (Au, Ag, Pt, Pd) as catalyst for chemical
etching in a solution containing HF acid and an oxidizing agent
[1÷8].
In this work, palladium is deposited as a catalytic metal by immersing
silicon wafers in PdCl2 aqueous solution [9÷12]. A metal
assisted etching in HF:H2O2:H2O forms a porous Si. The consecutive
chemical etching based on HF:HNO3 solution change the porous
structure into the textured surface, which is more convenient
for solar cells than the porous layer.
EXPERIMENT AL AND RESU LTS
Palladium clusters deposition
The p type polycrystalline silicon wafers with resistivity ρ of 0.5
to 2 &#[...]
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The application of artificial neural networks in designing single-segment processes of vacuum carburizing
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Piot r Kula Emilia Wołowiec
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Today’s rapid technical progress of civilization and growing expectations
of consumers forces equally fast development in all branches
of the mechanical industry. It also concerns thermochemical
treatment, in which traditional gas carburization is superseded by
a modern technology of vacuum carburization . The reason for such
a state of being is the high potential of carburizing atmospheres
of vacuum carburization processes, which reduces both the time
and costs of treatment of thermally improved machine parts. Nowadays,
universal vacuum furnaces constitute basic technological
equipment of state-of-the-art hardening plants as well as corporate
divisions in charge of thermal treatment in the aviation, automotive,
tool making and machine construction industries.
However, as opposed to gas carburization, vacuum carburization
is a much more complex process, which makes treatment with
the use of this method more difficult to control, and hence, enforces
more intensified control over the whole technological process.
Therefore, in recent years, we have been observing increased
demand for computer-aided tools (simulators) used to design and
simulate these processes.
A precise simulator requires an accurate model of a particular
phenomenon simulated, which will be the core of its calculations;
however, building such an accurate mathematical model is not always
possible or affordable. The application of the artificial intelligence
method, in particular artificial neural networks, is one of the
ways to simulate the process of carburization without the necessity
of creating a mathematical model [1, 11].
The following paragraphs briefly describe the essence and objectives
of research on the possibility of applying artificial neural networks
in the technology of vacuum carburization, the architecture
of a sample neural network that achieves this goal and examples
of vacuum carburization processes and single-segment processes
meeting [...]
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The application of grain size evaluation method on non-planar surfaces in the studies of aircraft engine turbine blades
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STANIS ŁAW ROSKOSZ
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In polycrystalline blades of aircraft engine turbines, the size and
shape of the grain constitutes one of the most significant quality
control criteria of the casts made. In industrial practice, the macrostructure
of the airfoil and the blade lock is evaluated in terms of
the presence of equiaxial, columnar and frozen grains. The grain
size has a significant influence on the mechanical properties, creep
resistance as well as heat-resistance of the blades [1÷5].
It is impossible to directly measure the size of the grain due to
the variable curvature of the airfoil surface. This requires measuring
the grain size on a non-planar surface of the blade airfoil, on the
basis of its perpendicular projection [6].
Research material
The research material consisted of three polycrystalline blades
produced from MAR M247, IN-100 and IN-713C alloys through
investment casting at WSK “PZL Rzeszów" S.A. The blades differ
from one other in their chemical composition, size and variable
geometry of the airfoil (Fig. 1).
Methodology
To detect the presence of primary grains in the investigated superalloys,
the airfoil surfaces were etched in a reagent of the following
chemical composition: 18 g/l HNO3, 280÷320 g/l HCl, 151÷173 g/l
FeCl3 (anhydrous) and 110 ml/l H2O. Before etching, the blade must
be degreased; the etching time is 5 seconds (Fig. 1).
To obtain an image of the airfoil projection, a stereoscopic microscope,
Olympus SZX-9, was used. Images were recorded in polarized
light at magnification of 10÷25×. Individual fields of view
were recorded by means of a ColorView IIIu digital camera. The
individual fields of view recorded[...]
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The computer aided pressure casting die
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Jacek Sawicki Marek Górecki Zbigniew Gawroński Łukasz Kaczmarek
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The demand for improvement of the quality of products is characteristic
of any purposeful human activity. One of the aspects of
product quality is their reliability. At the same time, the prevailing
belief is that the greatest possibilities to influence product durability
exist at the stage of design. In die casting today, a global market
for cooperation supplies has evolved where numerous companies of
various sizes and with different technical equipment compete with
one another. In order to meet the customers’ requirement in the face
of such fierce competition, the manufacturers of die castings must
continually improve their products, lower their production costs and
respond quickly and flexibly to new orders. A serious problem here
concerns the process of quick design and manufacture of die casting
dies and ensuring their high durability to achieve price competitiveness
of the final product. This is a difficult engineering problem due
to the highly individualised nature of the design and production of
every die, as it is hard to draw on previous experience. Additionally,
any optimization of the construction and technology of dies is
complicated due to the complex nature of wear processes including:
thermal fatigue, mechanical fatigue, erosion cavitation, dissolution
of some components of die material by liquid metal, adhesion of the
casting to the die, etc.
Die durability largely depends on the correct selection of materials,
heat treatment as well as the appropriately formed surface layer
preventing the occurrence of macrocracks, and at the same time delaying
the occurrence and propagation of thermal cracks for as long
as possible. More and more experience drawn from practice proves
the usefulness of such surface treatments[...]
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The corrosion resistance of 7475 aluminium alloy processed by hydrostatic extrusion
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EWA URA-BINCZYK ALICJA BALKOWIEC MAłGORZATA LEWANDOWSKA KRZYSZTO F JAN KURZYDŁOWSKI
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High strength 7xxx aluminium alloys are commonly used in aircraft
structure applications. Conventionally, they are precipitation
strengthened which makes them the strongest among aluminium
alloys. The grain refinement down to nanometre scale offers an additional
possibility to improve their mechanical properties as the
yield stress is a linear function of inverse square root of grain size
(Hall-Petch relationship). The efficiency of such an approach was
already confirmed in a number of studies [1, 2].
The size of grains can be efficiently refined down to nanoscale
via a number of processing routes, among others utilizing severe
plastic deformation. Such a processing enables micrograined aggregates
to be transformed into nanograined via accumulation and
rearrangement of defects, primarily dislocations, generated during
the deformation. Experimental observations showed, that for such
a transformation to take place, a large degree of plastic deformation
is required, which usually exceeds the maximum equivalent strain
achievable in simple plastic forming methods [3, 4]. As a result,
special deformation methods have been developed, e.g. equal channel
angular pressing and high pressure torsion. Also, it was recently
demonstrated that hydrostatic extrusion (HE) can be used to efficiently
refine the grain size in a number of metals and alloys [5,
6]. In comparison to the other SPD methods, HE usually requires
a significantly smaller total strain. This is primarily due to the high
strain rates, which frequently exceed 102 s-1 and reduce the extrusion
time to seconds. As a result, the work associated with plastic
deformation is more efficiently transformed into the energy of the
accumulated defects.
It was already established that nanograin refinement in SPD metals
results in a high strength not possible to obtain by other strengthening
mechanisms. However, it should be noted that wider industrial
applications of these materials are res[...]
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The degradation of mechanical properties of Al-Si5-Cu2-Mg and Al-Cu4-Ni2-Mg alloys after soaking at high temperature
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Małgorzata Wierzb ińska Jan Sieniawski Grażyna Mrówka-Nowotnik
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The application of aluminium alloys for aircraft industry is determined
by their properties - low density and high relative mechanical
strength (Rm/δ) in particular, good electrical and thermal conduction,
and very good technological properties - castability and
plastic deformability.
The progress of engineering and science in all aspects of world
aviation is inseparable connected to production and application of
aluminium alloys characterized by lower density and better mechanical
properties than other applied alloys. The casting aluminium-
-silicon-copper alloys with magnesium addition are widely used
in the aeronautical engineering. Silicon and copper (the main alloy
additions) improve the technological properties (fluidity and lower
solidification shrinkage), reduce the value of thermal linear expansion
- important factor for pistons production, improve the wear
resistance, tensile and fatigue strength. It is known that the addition
of Mg and Cu facilitates the precipitation of fine Mg2Si and Al2Cu
phases and therefore improves hardening [1÷12].
A great number of investigations have recently been devoted to
the effect of Cu, Ag and Sn addition on mechanical properties of Al
alloys. It was found that increasing of Cu contents causes increase
in tensile strength and yield stress of alloys with no harmful effect
on their plasticity.
Due to technological problems occurring during processing (microcraks
formation) the Al-Cu alloys are not used as a widely as
Al-Si-Cu alloys. Nevertheless they are commonly used as a base
material for multicomponents alloys. An example is quarternary
Al-Cu-Ni-Mg alloys containing up to 4.5% Cu, 2% Mg and 2%
Ni charcterized by very good thermal resistance to high temperatures.
This is due to presence of intermetallic phases Al6Cu3Ni and
Al2CuMg forming during primary crystallization and hardening
process.
The [...]
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The effect of heavy deformation on the structure of Mg-AZ31 alloy at ambientand elevated temperatures
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JAN BONARSKI JAN POSPIE CH
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Constructional Mg alloys like AZ31 (96 wt % Mg, 3 wt % Al,
1 wt % Zn) reveal relatively low density (63% of pure Al density)
together with good strength properties. However, their plasticity is
low as well as deformability at room temperature, documented in
the curves of nominal strain in dependence on relative strain shown
in Figure 1. Their shape indicates that exceeding the instability point
(maximum of the curve equivalent to Rm value) brings about nearly
immediate failure of the specimen. It leads to the conclusion, that
the ductility - a feature better describing deformability than elongation
- is low. The deformability of Mg alloy increases significantly
only at elevated temperature. The Mg‑based alloys, like AZ31 or
AZ91 alloy is usually hot-deformed with the use of conventional
methods like extrusion at least at 300°C [1].
Low ductility of hexagonal metals at low temperatures caused
by the deficiency of easy-activated slip systems decreases their
chance to use a method of Severe Plastic Deformation (SPD) as
a way of grain structure refinement. Since the deformation at high
temperatures is accompanied by the recrystallization process (dynamic
or static one), the advantageous effects of plastic deformation
are removed. That is why, cold pressing through an angular
channel using an ECAP (Equal Channel Angular Pressing) method
has become recently very promising when stable structure refinement
using SPD is to be achieved. The ECAP is a process of intensive
plastic deformation, in which the material is extruded with
change of deformation path in the angular channel [2], where it is
subjected to shear maintaining the dimensions of the cross‑section.
The mentioned already change of the deformation path as well as a
generated strong hydrostatic component of the strain field, is used
in the ECAP process to prevent from formation of cracks in conditions
of strong external constraints. The method enables to process
r[...]
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The effect of lattice distortion on the course of the martensitic transformations in NiTi shape memory alloys
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Danuta Stróż Dariusz Chrobak
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In the Ni-Ti system it is the B2 intermetalic NiTi phase that undergoes
the reversible martensitic transformation to the B19′ monoclinic
phase. For an alloy of any composition (provided it ensures
the B2 phase presence) cooled down very slowly the transformation
occurs always at the same temperature i.e. about 60°C. In the
Ni-rich alloys the precipitation process may take place that changes
the transformation characteristic temperatures and/or its sequence.
There are several variants of this process depending on the ageing
temperature [1], these are:
β0
→ β1 + Ni4Ti3 → β2 + Ti2Ni3 → β3 + TiNi3, Ta < 680 ± 10°C
β0
→ β′1 + Ni3Ti2 → β′2 + TiNi3, 680 ± 10°C < Ta < 750 ± 10°C
β0 → β″1 + Ni3Ti for Ta > 750 ± 10°C.
However, the most significant influence on the course of the martensitic
transformation in the NiTi alloy have the Ni4Ti3 particles.
The strain fields around these coherent precipitates as well as
the decrease of the Ni concentration in the matrix change the characteristic
transformation temperatures and cause occurrence of the
R-phase transition preceding the B19′ martensite formation. Similar
effects take place in the NiTi equiatomic alloys deformed and then
annealed at temperatures below the recrystallisation temperature. In
both cases additional effects in form of a multistage transformation
were often observed. The first data on the multistage martensitic
transformation were given by Todoroki and Tamura [2], Stróż et al.
[3] and Zhu et al. [4]. It was found that depending on the applied
thermal treatment there exist three or even four more or less overlapping
peaks on the DSC cooling curves. The occurrence of the
R-phase transition in these alloys is understandable as this transition
causes less lattice distortions and thus is favoured when the internal
stresses exist in the sample. Howeve[...]
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The effect of metallic inter-layers on multilayer ceramic/metal coatings properties
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Łukasz Major Marcin Kot Jürgen Lackner
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Wear resistant coatings are used to protect surface of industrial
components working under high and constant wear loads. Within
this group the ceramic hard coatings like titanium nitride (TiN) are
of special interest in a number of technological fields due to their
corrosion resistance and mechanical properties [1, 2]. The wear
of hard coatings can change dramatically with adjustment of parameters
like load, sliding speed, contact geometry and humidity.
Cracks initiation and propagation are often responsible for wear.
Nowadays it is a tendency to connect the properties of different
type of materials, like for example combination of hard and soft
phases in composite like coating or application of multilayer systems
where soft (metallic Ti) and hard (ceramic TiN) interlayers
are deposited in a sequence way [3÷5]. The Ti layers would allow
extensive plastic deformation at crack tip and also, due to a lower
elastic modulus compared to TiN, deflect the cracks. Consequently,
multilayered Ti/TiN coatings display an improved fracture resistance
as compared to homogenous TiN [6]. On one side the presence
of plastically deformed metallic layers play an important role
in cracks propagation mechanisms. Their presents can stop crack
propagation, on the other side the decrease of the amount of this,
metallic phase may have an influence on mechanical properties
like for example hardness. The current work is focused on how the
change of the ratio of ceramic phase to metallic one influence on the
microstructure and mechanical properties of coating.
Experimental
The hybrid PLD (Pulsed Laser Deposition + magnetron sputtering)
system equipped with high purity titanium target (99.9 at. % Ti)
was used for deposition of Ti/TiN multilayered coatings. The details
of deposition process is described in reference [7]. Two types of
coatings (with differ[...]
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The effect of structure on the stability of Al-Si coatings under salt mist conditions
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Joanna Wróbel Barbara Kucharska Zygmunt Nitkiewicz
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The high corrosion resistance of Al alloys, as well as their sufficient
heat resistance, have contributed to the use of these alloys for
anodic protective coatings being applied on steels intended for, e.g.,
exhaust system elements. Developing coatings that would meet the
ever-increasing operation parameters of cars is the subject of continuous
research work. The new customer demands, technological
solutions, and increasing car performance parameters are all urging
the designers to use increasingly expensive steel grades with bettered
mechanical parameters. However, a significant limitation on
the wide application of stainless steels is the fact that, in spite of the
absence of visible corrosion products, in acidified oxidizing media
containing some anions, these steels undergo spontaneous, often localized
dissolution. Due to the weight and economy of product, the
basic element used for protective coatings in the automotive industry
still remains to be aluminium [1÷4]. The problem of properly
selected protective coatings is crucial in the manufacture of car exhaust
silencers, because the whole exhaust system, in addition to
mechanical damage during service, is exposed to aggressive chemical
agents that accelerate the steel corrosion processes. At present,
steels of a chromium content above 10% with an aluminium-silicon
hot-dip coating applied are used for the manufacture of car exhaust
systems. Exhaust system elements are formed in a stamping process.
The main technological problem during their production from
aluminium-coated steel sheet is to maintain the integrity of the coating.
This problem has been partially solved by using silicon as an
alloying element. However, it has been demonstrated in the author’s
studies, that such coatings often exhibit an uneven arrangement
and size of silicon crystals (as a result of the trade-off between the
technical capabilities to produce a coating by the hot-dip coating
method and th[...]
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The elevated temperatures influence on the cobalt base cladding layer
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Hanna Smoleńska
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Many structural components contemporary used in engines, gas turbine
or industrial applications like for example: moulds for glass
and ceramics, automotive valves, chemical and petrol-chemical
valves, lamination cylinders, plastics extrusion screws and dies
[1] are subjected thermal, mechanical and chemical loads at the
same time. It needs materials which presented a good combination
of strength and hardness properties, corrosion and thermal fatigue
resistance and excellent fabrication. In modern technology hardfacing
by producing surface coating is often used. Such surface
coating can protect the parts from wear and, depending on coating
material selection, from chemical or high temperature corrosion.
Various processes such as spray and fusion, gas tungsten arc welding
and submerged arc welding process are used to the clad the
wear resistant layer. Among these different deposition techniques,
plasma-transferred arc (PTA) is one of the most interesting processes
because of its high deposition rate and low heat input and
especially for its wide range of material which can be used [2÷8]
also the deposits can be obtained with completely automated unmanned
machines. During recent decades, the high-temperature
oxidation on structural materials, such as Fe-, Co-, and Ni-base alloys,
for which high-temperature oxidation resistance is an important
parameter, has been investigated intensively. In general, these
alloys developed good oxidation resistance by possessing proper
amounts of Al, Cr, and Si and are called as alumina, chromia, and
silica formers. For chromia formers, maximum protection against
oxidation is obtained only if a continuous and coherent Cr2O3 scale
layer is formed and maintained. That alloys must have a sufficient
chromium content to initially form a chromium oxide and supply
of chromium by diffusion within the underlying alloy in order to
continuous growth of the protective scale. [9]. In spite of the long
history [...]
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The evolution of the gradient microstructure of the hard magnetic alloy FeCr30Co8 subjected to plastic deformation by tension combined with torsion
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Anna Korneva Galija Korznikova Magdalena Bieda-Niemiec Aleksandr Korznikov Marek Faryna Krzysztof SZTWIERTNI A
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The FeCr30Co8 alloy belongs to the hard magnetic materials of the
Fe-Cr-Co system [1]. Due to its good ductility, the excellent magnetic
properties and the low cost, it is used to produce permanent
magnets of various sizes and shapes, as wires, tubes, bars, and strips
[2, 3].
The high coercive state of the Fe-Cr-Co alloys can be obtained
in the process of a magnetic treatment and multi-stage tempering,
which resulted in a spinodal decomposition of an α solid solution
into isomorphous, ordered and coherent phases: magnetic α1 and
paramagnetic α2 [4]. The formation of such a structure, where each
precipitate of the α1 phase (with sizes of about 50÷100 nm) appears
as a single domain, provides high magnetic properties. On the other
hand, the microstructure (α1 + α2) causes a reduction of the material’s
plasticity and strength to the level of 200÷400 MPa. This is
a serious technological problem, since the commonly used industrial
magnets require strength greater than ~900 MPa. The brittleness
and the low strength of hard magnetic alloys in a high-coercive
(α1 + α2) state limit the possible range of their applications.
It is known that the magnetic and mechanical properties are dependent
on the microstructure: they are changing significantly with
the decreasing of the grain size, to nano- or submicron scale, and
with the alteration of the phase morphology or the phase transformation.
All these modifications of the microstructure can be achieved
by means of an intensive plastic deformation, which is considered
as one of the methods improving the material properties [5, 6]. In
order to achieve the refinement of microstructure with a gradient
character, the FeCr30Co8 alloy was deformed by tension combined
with torsion at 700, 750, 800 and 850°C. It is known that the gradient
microstructure results in gradual changes of material properties.
This can be beneficial in the case of magnets, which[...]
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The influence of grain size of Ni3Al alloy on cavitation wear of Ni3Al intermetallic after cold rolling and recrystallization during incubation period
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Dariusz Zasada Zbign iew Zarański Robert Jasionowski
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Unbeneficial phenomenon of cavitation is very common and can be
observed in many fields of life. In particular, it appears in hydraulic
machines and systems, and as well as in automotive and shipbuilding
industries. Cavitation wear has been a subject of many publications
and scientific works since the end of 19th century. However,
recent state of knowledge of this phenomenon is still insufficient.
Osborn Reynolds was the first who described this phenomenon in
1894. The meaning of term cavitation was taken from latin word
cavitas which means cavern, void. Cavitation was firstly recognized
as the reason of screw propellers and turbine rotors destruction at
the turn of the 19th century. The first accurate definition of cavitation
has been created in 20th century, and then material research
as an attempt to full explanation of this effect has been introduced.
Cavitation has been also noted in sliding vane-pumps, gear wheels,
pipelines and fittings.
Cavitational erosion is an effect of mechanical devastation of
material, due to implossions of cavitational bubbles in the nearby
or directly on material’s surface, what results in weight loss. Microbubbles
serve as a cavitation embryos, which can be periodically
recreated, due to release of gases from liquid. The effect of periodically
repeated compression and implosion of gas bubbles is accompanied
by rapidly changing impulses of pressure with value of even
1 GPa. Especially dangerous conditions can be achieved if microbubbles
form cavitational clouds, which can lead to simultaneous
implossion of large amount of bubbles and creation of very high
pressure impulse. Formation of accumulative beam of liquid which
moves with speed of 100 m/s, is also possible in critical conditions
[1÷5]. Surface zone strengthening, microcracks, material loss and
microstructure changes are appearing in the material as a result of
continous impact of pressure pulses [6÷8]. Special attention has
been f[...]
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The investigations of Fe-Al phases formation arround SHS reaction in isothermal conditions
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EWELINA POCHEĆ STANISŁAW JÓŹ WIA K KRZYSZTO F KARCZEWSKI ZBIGNIEW BOJAR
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The process of Fe-Al phases formation has been the subject of interest
for many years and it was described by many scientists. There
are a lot of different theories explaining the mechanisms occurring
during phases formation. One of the main theory was described by
Deevi and Gedevanishvili [1]. They observed, that during the heating
of Fe and Al powders mixture two exothermic reactions have
occured. At temperature range of 540÷560°C the self-propagating
high-temperature synthesis (SHS) [2, 6÷8] occurs and it is responsible
for formation of the hard and fragile Fe2Al5 phase. Next reaction,
at temperature range of 650÷670°C, leads to nucleation and
growth of FeAl secondary solid solution. It is the effect of interaction
between remaining iron and Fe2Al5 phase what was confirmed
by Gao and coworkers [3]. Wei-Jen and Wang coated mild steel by
hot-dipping in a molten aluminum bath and they obtained thin layers
of FeAl3 and Fe2Al5 phases [4]. Whole set of phases in the Fe-Al
system (FeAl3, FeAl2, Fe2Al5, Fe3Al and FeAl) was observed by
other authors after sintering process and SHS reaction [5, 10, 17]
The aim of this paper is to explain the phenomena occurs before
and during SHS reaction. It is very important to describe phases
transformations around SHS reaction, because they can influence
the final structure of Fe-Al sinters. The obtained results showed that
in sinter structure there are not only Fe2Al5 phase and aluminumlow
Fe(Al) solid solution but also high-aluminum FeAl2 and FeAl3
phases, formed prior the SHS reaction.
EXPERIMENTAL
Elemental powders of 99.8% pure iron with an average particle size
of 200 μm and 99.6% pure aluminum with an average particle size
of 70 μm were mixed at a steichiometric ratio of 50 at. % Fe-50
at. % Al in a Uniball 5 mill (without milling balls) for 1 h.
Than the cylindrical DSC specimens (3 mm in diameter and
20 mg in weight) were cold compacted uniaxially at a pressure of
700 MPa.
Ob[...]
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The microstructure of rapidly quenched Fe-Cu-based alloy with a liquid miscibility gap
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Tomasz Kozieł Zb igniew Kędzierski Anna Zielińska-Lipiec Jerzy Latuch
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Although superior properties of metallic glasses such as high
strength and high elastic limit, its application is very limited due
to highly localized shear banding [1, 2] and thus very low ductility.
Ductility of metallic glasses could be improved by formation
of composite materials consisting of crystalline phases dispersed
in the amorphous matrix. Such composites might be produced by
in-situ formation of the crystalline phase.
In 2004 Kündig et al. [3] for the first time showed two-phase
amorphous structure in metallic system. The system he studied included
one pair of elements with high positive heat of mixing (La-
Zr) while negative heat of mixing of the other elements (Al, Cu,
Ni) to both, La and Zr. Positive heat of mixing between two major
elements forced liquid phase separation into La-rich and Zr-rich
melts during cooling of the homogeneous melt below critical temperature
required for decomposition. Negative heat of mixing of
the other alloying elements to La and Zr, increased glass forming
ability of both separated melts. Rapid cooling enabled formation
of two glassy structures, La-rich and Zr-rich, with surface fractal
microstructure [3]. This work initiated research of systems based
on elements with positive heat of mixing and thus possible formation
of two amorphous phases. Several two-phase metallic glasses
were reported up to date including Y-Ti-Al-Co [4], Ni-Nb-Y [5],
Ag-Cu-Zr [6], Cu-Zr-Al-Y [7] and Nd-Zr-Al-Co [8].
Since two-phase amorphous structure was obtained, one can
expect different thermal stability of both glassy phases. Thus formation
of amorphous-crystalline composites with nanocrystalline
structure is possible by partial devitrification of one of the amorphous
phases.
This work deals with another system based on two elements,
namely Fe and Cu, with positive heat of mixing as high as
+13 kJ/mol [9]. Although the Fe-Cu phase diagram does not contain
a liquid miscibility gap, Turchanin et al. [10] p[...]
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The process of glow discharge assisted oxynitriding of titanium alloy in aspect of its application in artificial heart components
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Tomasz Borowski Agnieszka Sowińska Maciej Ossowski Elżbieta Czarnowska Tadeusz Wierzchoń
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Medical industry is constantly searching for new biomaterials, that
may meet the requirements connected with their application. The
best biocompatible metallic materials are titanium and its alloys
which besides their good biocompatibility have low density and
high mechanical properties [1÷4]. They are widely used for among
others osseous implants, osseous fixation elements, pins, plates and
screws, elements of dental implants and medical instruments [5]. In
order to improve resistance to frictional wear, corrosion resistance
and fatigue strength, as well as to eliminate occurrence of metalosis
and improve biocompatibility of titanium materials various methods
of surface engineering are successfully applied [1, 6÷8]. Application
of surface engineering methods to give antithrombogenic
properties to titanium alloys used in artificial heart or other components
contacting with blood is a new challenge.
The latest research shows that titanium oxide is a prospective
hemocompatible material. Most of currently conducted research
works dealing with hemocompatibility of titanium oxide regards
layers made on polyurethane, polyethylene or pyrolytic carbon
(LTI-carbon) substrate. Examination of hemocompatibility of oxide
layers produced on siliceous substrate with a method of plasma
immersion ion implantation and deposition (PIII-D) revealed better
biocompatibility of these materials in contact with endothelium
cells as well as antiadhesive properties of layers of crystal structures
in comparison with layers of amorphous structure [9, 10]. Various
methods of oxide layers modification are being searched for. For
example doping with lanthanum oxide impurities La2O3 of TiO2 layer
made with an application of RF-magnetron sputtering method on
silica substrate considerably increases hemocompatibility of produced
layers and reduces coagulation of blood platelets [11]. Successful
attempts of improving biological properties of pyrolitic low
tempera[...]
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The zinc coating solidification on surface silicon steels and DI castings
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Dariusz Kopyciński Edward Guzik Waldemar Wołczyński
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Hot dip galvanizing of reactive steels with high silicon content is
a very interesting problem still lacking a complete and practically
acceptable solution, although the currently used practice of steel
making forces in a way the use of high silicon levels. An important
issue in hot dip galvanizing is the phenomenon of the formation
of a thick, brittle and dull-grey coating when the content of silicon
(and phosphorus) in steel exceeds the critical but quite commonly
used level, expressed by equation (1):
(Si + 2.5P)·103 = ESi,P (1)
Below this value, the obtained coating is characterized by a correct
glossy finish and ,,normal" thickness, while above the critical
level of silicon and phosphorus equivalent the coating loses its adhesive
force and as such can have poor adhesion, which means that
the zinc volume necessary to produce the finally required coating
thickness may be too large and therefore too expensive.
As follows from the studies described in [1÷4], the chief solution
to the problem of a wide range of the silicon and phosphorus
equivalent values in steels (so more in cast iron) available at present
in the domestic market seems to be a conformity certificate specifying
precisely the composition of the steel used for elements which
are to be subjected to the galvanizing treatment or proper selection
of steel already at the stage of designing or making these elements
(as far as it is possible). Procedure of this type should be effectively
implemented in the galvanizing plants which use a wide spectrum
of different steel grades, while the plants which make on request
galvanizing of single elements should try to optimize the composition
of the zinc bath they commonly use.
Recently, some novel solutions have been offered in the field of
hot dip galvanizing. One of them, widely used by industry, is the
process of zinc-nickel galvanizing [5÷8]. The process of hot-dip
galvanizing in Zn-Ni bath is at present considered to[...]
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Thermal stability of Ni3Al-based intermetallic alloys structure upon long-lasting annealing
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Paweł Jóźwik Wojciech Polkowski Zbigniew Bojar
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Intermetallic alloys present a group of intensively investigated hightemperature
structural materials. A lot of work has been focused
on Ni3Al-based alloys. Due to large aluminium content and high
degree of structure ordering, these alloys posses some advantages
over actually applied nickel-based superalloys [1]:
-- much better oxidation and carburization resistance at temperature
up to 1100°C,
-- good mechanical strength at high temperature (with effect of an
anomalous temperature dependence of yield strength),
-- excellent wear resistance, also at high temperature,
-- relatively low density and costs of raw materials.
However, the main drawback in wide commercialization of
Ni3Al-based alloys (and other intermetallic-based materials) is
their low fracture thouhgness and, related with that, problematic
manufacturing and processing of these materials. The problem of
Ni3Al-based alloys brittleness has already been prominently reduced
by the modification of chemical composition (e.g. by alloying
with small amounts of boron and zirconium [2, 3]) and development
of effective manufacturing technologies [4], what has
resulted in few successful industrial applications of these materials
[5]. The current applications of Ni3Al-based casting alloys include,
e.g. heat treating trays and fixtures for carburizing and air
environments, transfer rolls for austenitizing furnaces, forging dies
and special components. Additionally, Ni3Al-based alloys in the
form of cold-rolled thin foils (with thickness even below 50 μm)
are considered as promising substrate material for applications in
microelectromechanical systems (MEMS). Ni3Al thin foils formed
in so-called honey-comb structures can also be applied in electrochemical
systems such as catalytic production of hydrogen from
methanol system [6]. Neverthless, an quantitative description of relationship
between structure and properties of Ni3Al-based alloys is
rather difficult, due to their h[...]
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Thermodynamics of Cu-Sn-X (X=Bi, Nb, Sb, Zn) liquid alloys
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Jolanta Romanowska
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A fundamental goal in materials science is to be able to control the
final physical or chemical properties of a material. In order to do
that one must understand the relations between raw materials, their
chemical composition, processing conditions, microstructure and
properties of the final material. During processing, and often in use,
most materials undergo reactions and phase transformations. This
is particularly obvious in melt processing where materials are completely
or partially melted and then solidified. Phase diagrams are
the fundamental aid for understanding interrelations between chemical
composition, processing conditions and microstructure. Since a
phase diagram is a representation of the thermodynamic properties
of a system it is possible to calculate it, unless the thermodynamic
properties are known. By combining the knowledge on the phase
diagram and the thermodynamic properties a model description of
the system suitable for phase diagram calculations can be created.
Descriptions of low order systems can be combined to make
extrapolations to higher order systems. For this purpose the Gibbs
energy of each phase is described by a suitable model containing
a relatively small number of variable coefficients. The thermodynamic
properties of a binary system can be calculated using the
Gibbs free energy expression comprising contributions of both
elements in each phase existing in the system. Further parameters
are introduced to describe the mutual interaction between elements
in each phase. Difficulty in extension of the calculated results to
higher order systems is much less than in the case of experimental
work, since the essence of the calculation does not change so much
between a binary system and a higher order one [1].
Sometimes, due to the lack of experimental data for ternary systems,
parameters for ternary systems are calculated on the basis
of values for binary ones and different simplifications and models[...]
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Transport properties of nanocrystalline and microcrystalline Gd-doped ceria
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Guido Baldinozzi Mickael Dolle Jan Kusiński Claude Petot Georgette Petot-Ervas
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Solid oxide fuel cells (SOFC) are regarded to be amongst the cleanest
and most efficient technologies for chemical-to-electrical energy
conversion. However, to be economically competitive it is necessary
to lower their operation temperature in the range 500÷600°C.
This provides several advantages, including lower degradation rate
of both components and cell performances and lower fabrication
cost through the use of less expensive materials for interconnections,
heat exchangers and structural components. To realize the
lowering of the operation temperature, there are different options,
the use of thin-film electrolytes or new solid electrolytes with high
ionic conductivity, for instance, because this component is the main
material of SOFC, whose structure and properties affect directly the
fuel cell efficiency.
Ceria based oxides have been considered as one of the most suitable
alternative [1÷3] to yttria stabilized zirconia (YSZ), the solid
electrolyte utilized up to the present time in conventional SOFC,
operating at around 1000°C. This is due to their higher oxygen-ion
conductivity (0.025 Ω-1cm-1 at 600°C) compared with ZrO2-based
materials (<0.005 Ω-1cm-1). Furthermore, these oxides enhanced
electrode reactions due to an electrocatalytic effect via the Ce+3/Ce+4
couple, resulting in a mixed conductivity zone at the electrode level
(solid electrolyte/electrode material interface) which leads to a decrease
of the electrode resistance.
Recently, the use of nanocrystalline polycrystals was considered
as a promising approach to improve even more fuel cell performances.
Indeed, given the high surface-to-volume ratio of nanoceramics,
these materials possess a wide range of original properties [2÷6]
due to the high grain boundary density and interfacial surface, such
as enhanced mechanical properties and chemical reactivity. To date,
the impact of the reduction of grain size from the microcrystalline
range into the nanocr[...]
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Tribological behaviour of Fe-Al intermetallic coatings obtained by HVOF method
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Cezary Senderowski Zbigniew Bojar Bolesław Formanek Krzysztof Szymański
|
One of the current challenges in materials science is to find versatile
materials able to withstand a good resistance for different service
performance situations. Currently, intermetallic compounds are being
investigated as a good compromise for the good mechanical
properties, corrosion, oxidation and wear resistance. Much attention
has been paid to iron-aluminium (Fe-Al) intermetallic compounds
because of their potential applications as either high-temperature
bulk materials or coating materials. They show relatively high melting
points, high thermal conductivity, relatively low density and low
cost as well as excellent anti-oxidation and anticorrosion properties
as compared with Fe and Ni-based superalloys [1÷3]. Especially,
FeAl intermetallic compounds containing 35÷50 at. % Al possess
good resistance to oxidation and sulfidation corrosion, due to formation
of protective alumina scale at elevated temperature in aggressive
working conditions [3, 4]. Its applications include, among
others, molten salt systems for chemical air separation, automotive
exhaust systems and coal conversions systems.
In a previous study, the oxidation behaviour of HVOF and Dgun
sprayed FeAl coatings was already reported [5, 6]. Xiao et al.
[3] reported that the sulfidation resistance of HVOF sprayed FeAl
coating can be effectively improved by doping with CeO2 at an optimum
dosage of 2÷5 wt. %. Iron aluminides have been also proposed
lately as promising materials for wear applications. Many researches
[7÷11] have focused their attention on the friction behaviour of
FeAl coatings, emphasizing the role of the Fe-Al type intermetallic
phase as a new matrix to embed ceramic particles and replace the
extensively studied WC-Co cermet system for abrasive environments
in high temperature.
Friction has been the most investigated mechanism and delamination
was found to be the predominant cause for volume loss in
coatings [7÷9]. The other two wear mechanisms, [...]
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Ultra-fine grain structure of AA3104 alloy analyzed by TEM and SEM orientation mappings
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Henryk Paul Thierry Bau din Anna Tarasek
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It has been frequently shown that the application of electron backscattered
diffraction (EBSD) and high resolution scanning electron
microscopy (SEMFEG) to structure and texture analyses of cold
deformed and/or lightly annealeded materials gives reasonable results
only up to moderate strains (~1.5). In the case of higher deformations,
the resolution of SEM/EBSD technique is not always
sufficient. The application of systems of local orientation measurements
based on transmission electron microscopy (TEM) is one of
the ways towards the solution of the problem. Because of the good
spatial resolution (which is usually estimated to be below 10 nm
[1]) and the accuracy of orientation determination (better than 0.1°)
the local orientation measurements in TEM appears to be the suitable
method for the investigation of fine grained structures. Recent
studies leading to designing a fully automatic TEM system are focused
on automatic indexation of transmission Kikuchi bands, e.g.
[2÷5]. The application of fully automatic indexing in TEM is more
difficult than in the case of SEM mainly due to smaller acquisition
angle and higher indices of the diffraction planes as well as because
of poorer quality of diffraction patterns. The latter ‘parameter’ depends
not only on the dislocation density (surface strains) but also
specimen thickness. Moreover, according to Schwarzer [2] the accuracy
of the system by the use of automatic indexing was proved
up to 0.5°, whereas it is only 0.1° by manual indexing. Thus manual
indexing is still widely used for accurate determination of crystallographic
orientations.
They are other problems related to the acquisition time and long
range drift. The pattern acquisition is still the main factor determining
the time needed for map creation (usually ~25÷30 patterns per
minute). Additionally, the intensities in the original patterns significantly
decrease with the distance from the center of the image. Th[...]
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Ultrasonic method applied to defects identification in the forging ingots
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Józef KOWALSKI Jolanta DEDA Anna Maria JANUS Robert MARTYNO WSKI Waldemar WOŁCZYŃSKI
|
The typical massive forging ingots produced in the steelwork has
a mass of about 10÷100 T (Fig. 1).
According to the technology of casting a porosity is expected
along the ingot axis (Fig. 2). Each forging ingot is subjected to an
ultrasonic test at a production line. But the result of this kind of industry
test are not evident. In the case of the ingot of the mass about
12 T the acoustic signal indicated porous less than 1 mm longue
(reduced distance).
However, in the case of the ingot of the mass about 50 T the
acoustic signal was completely damped by the grains boundaries so
that no results of acoustic measurement were obtained.
Therefore, some additional tests have been made by means of the
light microscopy (LM) and scanning acoustic microscopy (SAM)
for six samples along a given radius of the ingot shown in Figure 1.
EXPERIMENTAL
The results of the microstructure observation are shown in Fig. 3.
A morphology of a one defect can be shown in more details
(Fig. 4).
The light microscopy is not able to reveal all the details of morphology
of some single defects as these shown in Figures 3 and 4.
Therefore, an attempt to identify the details of some defects was
done by the scanning acoustic microscopy (Fig. 5, 6, 7a).
Identification of the defects is performed by the SAM technique
through density analysis of the different sample sublayers (Fig. 6).
Microscope reveals a defect by comparison of the difference between
density of bulk sample and density of a given defect.
It is possible because scans can be made at different fixed distances.
˗
Fig. 1. Massive forging ingot produced in the steelwork
Rys. 1. Masywny wlewek kuzienny produkcji hu[...]
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XRD investigations of electrodeposited Ni and Ni/Al2O3 coatings
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ANNA GÓRAL EWA BEŁTOWSKA-Lehman
|
Recently, metal matrix composite (MMC) coatings containing ceramic
particles have been widely investigated due to their enhanced
material properties (i.e. higher hardness, wear and corrosion resistance)
compared to the pure metal or alloy [1÷4]. The MMC properties
depend mainly on the type, structure, shape, size, morphology
and content of the inert ceramic particles as well as on their distribution
in the metal matrix. Several metals, e.g. nickel, copper,
gold, chromium have been mainly used as a metal matrix, whereas
metal oxides, carbides, borides and polymers were the co-depositing
particles [5]. Electrolytic nickel coatings exhibit specific properties
as hardness, durability, good corrosion resistance and catalytic
activity in many electrochemical processes [6]. The addition
of hard ceramic particles into Ni matrix can improve its hardness
and wear resistance. These phenomena are mainly attributed to the
hardening of the metal matrix by finely dispersed ceramic particles
[7]. Al2O3 particle has many superior properties, such as low price,
good chemical stability, high microhardness wear resistance at high
temperature [8]. Insoluble particles are suspended in a conventional
electrolytic bath and embedded in the growing metal during co-deposition
process. The Ni/Al2O3 nanocomposites are one of the most
promising materials, that can find wide engineering application as
coatings of engine cylinders, high-pressure valves, car accessories,
aircraft microelectronics etc. [9÷10]. Functional properties of electrodeposited
composites are mainly controlled by their composition
and structure. Among others, they depend strongly on their microstructure,
residual stresses and due to the anisotropic properties on
the distribution of crystallographic orientation.
It is widely accepted that the state of residual stress on the coating
surface and in the near surface area is one of the most important
parameters of surface deposit quality. Mac[...]
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