Ni-Mo alloys are characterized by high hardness, wear, thermal and corrosion resistance [1, 2]. Due to this reason they could offer an important alternative to hard chromium coatings, which according to EU directives (2000/53/WE, 2011/37/UE) have to be eliminated from manufacturing processes [3]. However, these alloys are difficult to obtain by conventional thermal methods, what is caused by the large difference in metals melting points (Ni . 1455 C, Mo . 2620C) and the limited mutual solubility. Convenient way to produce these type of coatings, which overcomes above mentioned problems, is a low-temperature and relatively simple electrodeposition technique. It enables uniform surface covering with simultaneous control of thickness and microstructure and thus allow to influence the properties of the layer. The mechanism of Ni-Mo alloys electrodeposition is still not clearly understood, although a few hypotheses are presented in the literature [4?€7]. Nevertheless, it is known that molybdenum (as well as another reluctant elements, such as W, Ge) cannot be deposited alone from aqueous solution of their salts. However, it could be readily co-deposited with iron-group metals (such as Ni, which acts as a catalyst) with an alloy formation. This phenomenon was called induced co-deposition by Brenner [8]. However, Ni-Mo coatings deposited from solution containing only molybdenum and nickel ions are of poor quality and contain high amount of molybdenum oxides. This effect is probably related to the formation of multimolecular heteropolymolybdates, which are difficult to electroreduce. Addition of an appropriate complexing agent, such as sodium citrate (characterized also by buffering, leveling and brightening properties), causes decomposition of heteropolymolybdates and the formation of the electroactive molybdenum [MoO4(Cit)H]4. and then nickel [NiCit]. citrate complexes (Cit = C6H5O7 3.) [9]. It results in an im więcej » Czytaj za darmo! »

Turbine blades, vanes, and other parts of aero engines exposed to high temperature are produced of nickel-based superalloys via investment casting. Directional solidification (DS) allows obtaining excellent mechanical properties of blades [1]. Because turbine blades are flight safety parts, they must be free of any defects. However, directional solidification is very complex and many casting defects may appear during this process [1]. The commonly defects in DS and single crystal (SX) castings are freckles [1÷6] and stray grains [7÷9]. Freckles are casting defects that appear on the surface of DS or SX castings in the form of long chains of equiaxed grains aligned parallel to gravity [1÷6]. Freckle dimensions depend on casting dimensions: the length is usually the same as the casting, but the width is from one to several millimeters. Freckles are enriched with elements segregated to the liquid phase during solidification [2÷4]. Compared with the freckle-free part of a casting, freckled areas are characterized by an increased carbide content, γ + γ′ eutectics, and porosity [4]. Freckle formation is attributed to thermosolutal convection and buoyancy forces in the mushy zone, which are in turn caused by density inversion in the interdendritic liquid [5]. The tendency for various superalloys to freckle is characterized by the freckling index F, which depends on the chemical composition [1]: F C C C C C C = + + - + Ta Hf Mo Ti W 1 5 0 5 0 5 1 2 . . . . Re (1) where CTa, CHf, CMo, CTi, CW, and CRe are the concentration (wt %) of tantalum, hafnium, molybdenum, titanium, tungsten, and rhenium, respectively. In case of F > 1, the freckling tendency is low. The density inversion of interdendritic liquid in the mushy zone is caused by strong segregation of some elements (i.e., W, Re) into the solid phase. Therefore, during directional solidification, these elements are depleted in the liquid alloy in interdendr więcej » Czytaj za darmo! »

Microhardness of a material reflects the elastic-plastic properties around the point of measurement. It is also a very sensitive indicator of changes in both the microstructure and properties due to a heat treatment or mechanical treatment, and the process of aging that occurs in materials during operation [1?€6]. Microhardness measurement taken under the conditions of low testing loads allows making a number of indentations in selected areas of the sample. For example, in the material with a multiphase structure, like the creepresistant austenitic cast steel, the size of the indentation (depending also on the amount of load applied) represents, in most cases, the average microhardness of a matrix with the precipitates of different origin (Fig. 1). Microstructure of this material is characterised by a relatively small volume content of large and hard precipitates, and a soft matrix with fine secondary precipitates [4]. When the random microhardness measurements are taken at different points on the sample cross-section, a map of the microhardness values can be created in the form of a microhardness distribution density function reflecting local microstructure of the examined material. This means that to various peaks in this distribution one can assign the presence of different structural components, such as a relatively homogeneous matrix, matrix with increased number of fine precipitates, and matrix with large precipitates [3?€6]. The aim of this study was to use the results of the random HV0.01 microhardness measurements to describe changes in the microstructure of 0.3C-18Cr-30Ni cast steel with an addition of titanium, where the said changes have occurred as a result of annealing at a temperature of 800?‹C. EXPERIMENT Studies were conducted on the creep-resistant austenitic cast steel (Tab. 1) melted in an open induction furnace with acid lining [5]. Test ingots were annealed in air at 800?‹C for 10, więcej » Czytaj za darmo! »

Magnetic shape memory alloys (MSMA) have received considerable attention owing to their outstanding magnetoelastic and magnetocaloric properties [1?€3]. Among various MSMA the Heusler Ni-Mn-Sn alloy system has been identified as a promising alternative to the most widely studied Ni-Mn-Ga alloy, whose applications are limited by high Ga cost, poor ductility and low martensitic transformation temperature (Ms) [4, 5]. Ni-Mn-Sn is an off-stoichiometric intermetallic compound featuring L21 Heusler structure in the high temperature austenite phase. It may undergo temperature, stress or magnetic field induced martensitic transition to a lower temperature modulated martensite phase [6]. The magnetic field provoked behaviour is in this case similar to the usual shape memory effect occurring due to the heat induced reverse transformation, and therefore it is termed metamagnetic transition as opposed to Ni-Mn- Ga, which transforms from austenite to martensite in the presence of a sufficiently high magnetic field. The coupling between magnetism and structure observed in these alloys entails that the magnetic field can induce not only an entropy change of magnetic contribution (?˘SM) but also a supplementary fraction related to the latent heat associated with the structural transformation (?˘SS ). Entropy changes up to 10.4 J/kgK at 10 kOe has been reported for Ni-Mn- Sn alloy system [7]. Increased entropy changes may be utilized for magnetic refrigeration, which is of fundamental importance from the environmental point o view. The Ms and TC of the martensite phase are found to be strongly dependant on composition whereas TC of austenite is less sensitive to it [8]. The phase transition temperature dependence on composition is mainly attributed to the change in valence electron concentration (determined as the number of 3d and 4s electrons of Ni and Mn and the number of 5s and 5p electrons of Sn and expressed in terms of electron to więcej » Czytaj za darmo! »

CMSX-4 is a single crystal nickel-base superalloy, applied for aircraft and stationary gas turbine blades. Its microstructure consists on the cuboidal precipitates of ?Á?Ś phase (Ni3Al-based), coherent with ?Á solid solution matrix. Chemical composition of CMSX-4 superalloy contain s more than 10 chemical elements and is especially designed to achieve around 70% volume fraction of ?Á?Ś phase. The ?Á.?Á?Ś interfaces, separating the disordered ?Á solid solution and ordered ?Á?Ś phase precipitates, are the strong obstacles for dislocation movement, what allows to obtain the high temperature strength. During exploitation, the turbine blades are subjected to the load by centrifugal force at high temperature in the range from 700 to 1100?‹C, thus undergo creep deformation. The parts of the turbine blade work at different temperatures and stresses, therefore microstructural changes caused by creep must be investigated over a wide temperature.stress range. Depending on the temperature and stress, three creep regimes with distinct modes of predominant microstructural changes in single crystal superalloys can be distunguished [1]: .. at intermediate temperature (700?€850?‹C) and high stress (550?€900 MPa) a pronounced primary creep deformation up to even 5% occurs at the very short time of several hours, .. at high temperature (850?€950?‹C) and medium stress (150?€550 MPa) the tertiary creep is dominant with the creep strain increasing monotonically with creep strain, .. at high temperature (900?€1200?‹C) and low stress (50?€185 MPa) the creep curves display small creep-hardening and a distinct plateau, during which the creep strain is almost not varied with time, followed by the pronounced increase of creep strain leading rupture. The microstructural changes caused by creep of CMSX-4 superalloy at the above mentioned creep regimes have been investigated by many researchers, e. więcej » Czytaj za darmo! »

Civilizational progress has a strong focus on improving properties of construction materials and their production technology. Due to the fact that so far, the steel is one of the basic construction materials the primary focus is exerted on the heavy industry. A phase transformation occurring during tempering of steels depends not only on the carbon content in the martensite and in retained austenite, but also on the content of various alloying elements. Tempering reduces the hardness, residual stress, but increases the ductility. The reduction of hardness is the inevitable consequence of improved strength. The structural changes that occur during the tempering of steels depend on the temperature, time of the process and the concentration of carbon. During tempering of steels, occurred two unfavorable effects of decrease the impact strength. The first in the temperature range of 200?€350?‹C (referred to as irreversible temper brittleness) and the second in the range of 450?€600?‹C (called the reversible temper brittleness). Both of the effects continue to inspire many researchers. The aim of this study is to explain influence of the kinetics of phase transformations during tempering on the fracture toughness of model steel with different carbon content. Optimum mechanical properties are achieved by proper design and careful implementation of heat treatment technology. Above all, it is necessary to avoid the temperature range 250?€400?‹C, in which the temper brittleness occurs. Decrease in fracture toughness of steel tempered at this temperature range may be due to the destabilization of retained austenite [1?€5]. Also, due to the non-uniform dissolution of martensite (preferential along the primary austenite grain boundaries) [6, 7], or by growth of cementite precipitations, which formed easy way of cracking [8?€15]. Another theory explains the temper brittleness by the cementite więcej » Czytaj za darmo! »

Aluminium matrix composites (AMCs) have gained a considerable interest in automotive and aerospace applications due to the light weight combined with higher stiffness, elastic modulus and strength, as well as better thermal stability and wear resistance compared with conventional alloys [1?€9], So far, in this group of materials most of the attention has been paid to Al2O3 [1?€3] and SiC [3?€5] reinforced composites. Some of them are now well developed and have been already commercially applied [4, 5]. However, constant efforts are being made to improve existing materials and to design new ones in order to meet the increasing demands for advanced structural and functional materials. Recently, an increasing attention has been paid to aluminium nitride as a reinforcing phase in AMCs. The addition of AlN, due to its good physicochemical, mechanical and thermal properties, allows to enhance the modulus, strength, hardness, wear resistance and high temperature performance of aluminium alloy matrix [6?€9]. The main advantage of the aluminium nitride over commonly applied in AMCs reinforcing phases is good bonding to aluminium matrix, higher wettability in aluminium, as well as stability of aluminium/ aluminium nitride interface [9?€12]. In conventional metal matrix composite production a reinforcing phase is usually prepared separately, prior to the composite fabrication and introduced into the matrix via powder metallurgy [3, 6?€9], spray deposition, casting techniques [1, 2, 5] etc. These, referred to as ex-situ techniques, have one major disadvantage, which is generally weak bonding between the reinforcements and the matrix. A possible solution to this problem are in-situ techniques, in which the reinforcement is produced directly in the metallic matrix, e.g. by chemical reactions betwe więcej » Czytaj za darmo! »

Composite coatings are one possibility to increase the durability and performance of materials for different applications and protect them from detrimental effect of the environment. Metal matrix composite reinforced with ceramic particles generally find wide range of engineering applications due to their enhanced hardness, better wear and corrosion resistance when compared to pure metals or alloys [1, 2]. The most sought after method of producing these kinds of composites is electrodeposition, owing to its advantages like low cost and the operating temperature. Electrodeposition of metals reinforced with dispersoids (mainly oxides or carbides) is an important technique for production of functional coatings. Such coatings are required in different fields of industry including: machinery and various device construction, machining tools, automotive and aircraft parts etc. Nickel composite coatings containing ceramic particles are used as protective coatings [3]. The plating bath for electrodeposition of Ni/Al2O3 composite coatings is frequently used a standard Watts solution with addition of alumina powder. The amount of ceramic particles incorporated into nickel affects the microstructure and properties of electrodeposited nickel composite coatings. The structure and properties of composite coatings depend not only on the concentration, size, distribution, and nature of the reinforced particles, but also on the type of used solution and electroplating parameters (current density, temperature, pH value etc.) [1, 4]. Although the Ni/Al2O3 composite coatings have been improved significantly, certain problems persist with respect to their preparation. The volume content of alumina particles in Ni/Al2O3 coating cannot be controlled quantitatively and the particles are frequently agglomerated in the composite [5]. The small inert particles like nanoalumina are difficult to embed into deposited layer because of their dispersion difficu więcej » Czytaj za darmo! »

Nature offers us multitude of structures in plants and animals. From the beginning the human being have been fascinating of structure and functionality of natural creatures as for example flying of birds and bats. Bio-inspired materials are becoming of increasing interest in many engineering applications. The natural structures gain the superior physical and mechanical properties by hierarchical structures. Such a materials inspired scientists and engineers. The part of the science dealing with using natural templates in engineering solutions is called biomimetics, bionics or biomimicry [1]. However, the experience in this area is that it is not possible to create a new engineering materials simply by making a direct copy of biological materials. The paper presents the perspectives of biomimetics in materials science and engineering. The background of biomimetics and directions of development are described. State of the art There is no doubt that we can learn from Nature and adopted that knowledge to our engineering solutions. In 1917 D’Arcy W. Thomson in his book “On growth and Form" [2] suggested that organic forms can be described by physical and mathematical lows. There are some papers and books, which have been written to show the biological structures, their properties and potential as a new concept in many areas also in materials science. For example, work of J. Benyus from 1997: “Biomimicry: Inovation inspired by Nature" [3], papers and books of Vincent, Currey, Mann, Meyers, and others could be mentioned [4÷8]. In polish language in this area is the work of M. Wit from 1936 titled: “Mistrzostwo Natury" [9]. The work of M. W. Grabski and J. A. Kozubowski published in 2003 “Inżynieria materiałowa, geneza, istota, perspektywy" [10] with one chapter “Biomimetyczne perspektywy inżynierii materiałowej" and work of R. Pampuch from 2008 “Pomaga żyć, ceramika wczoraj i dziś" [11] wit więcej » Czytaj za darmo! »

The development of new generation of high-speed electrical devices requires high strength characteristics of magnetic materials used. Most magnetic materials of today reveal high magnetic characteristics but are brittle and have low ultimate rupture strength. The highest level of mechanical properties is realized in magnetically hard alloys of Fe-Cr-Co system. Fe-Cr-Co based alloys belong to the deformable magnetic materials of the precipitation-hardening class. Due to their good ductility, excellent magnetic properties and low cost, they are used for the production of permanent magnets of various sizes and shapes, such as wire, tube, bar, strip magnets, etc [1ˇŇ3]. A high-coercive state is obtained by a magnetic treatment and multistage tempering. This leads to the decomposition of the solid solution into the isomorphous Ł\1 and Ł\2 phases, containing ordered and coherent precipitates [4, 5]. The formation of such structures, in which each precipitate of the Ł\1 phase is a single magnetic domain, provides superior magnetic properties. However, internal stress fields, which originate from the formation of coherent boundaries between the precipitates of the Ł\1 and Ł\2 phases, cause a reduction in ductility and strength. It is known, that the structure of material and its mechanical properties can be changed using severe deformation techniques [6, 7]. Complex loading by compression, strength and torsion at an elevated temperature is rather a new method of severe plastic deformation [8]. It ensures a substantially refined microstructure without changing the shape of the specimen. Depending on the mode of the deformation chosen, this method allows localizing strain in specific regions and ensures the formation of gradient microstructure with different combination of magnetic and mechanical properties [9, 10]. The aim of the present work is to present the results of the microstructure and hardness investigations of the FeCr30Co8 a więcej » Czytaj za darmo! »

The objective of this paper is the analysis of the microstructure of a traditional scythe blade (Fig. 1). The scythe, first recorded about 500 BC and introduced into Europe in the 12th century, is an agricultural hand tool for mowing grass and reaping crops. It was widely used for many centuries until replaced almost completely by mechanical apparatus in the XX century. However, the scythe is still used today in many smaller farms for cutting down extensive areas of long grass, bracken and weeds. Recently scythes have been making a comeback in American suburbs due to the following advantages: the quietness of operation, the lack of necessary fuel, and the fact that it does not overheat, as do many machines. It also provides physical exercise for the user [1]. The traditional scythe consists of a long, wooden shaft (about 1.6 to 2.0 m) and a long, curved blade (about 0.6 to 0.9 m). The blade?fs cutting edge is on the inner side of the curvature, making mowing and collecting plants more convenient. During use the blade quickly becomes blunt and therefore requires regular sharpening. After a series of sharpenings, the blade is subjected to a peening process, during which the edge is plastically thinned by a hammering process, which enables further sharpening thus extending its working life. Peening increases the hardness of the metal on the edge as well as thinning the blade. The process itself is difficult and requires a much experience. Incorrectly performed, peening can cause a blade to fold and damage the scythe. The hammering resembles severe plastic deformation processes currently used for nanost więcej » Czytaj za darmo! »

In past few years tremendous scope of advanced and interdisciplinary research at field of biomaterial properties was evaluated. Investigations particularly bring closer relations between ?gliving tissue?h and biomaterial surface [1]. Manipulation at the level of surface morphology its physical state and most of all chemical composition, brings direct impact on tissue-implant integration that was confirmed in different approaches [2?€4]. The tissue, for example, may improve cell proliferation in respond to proper chemical composition, energy state or surface roughness [5]. Its spreading and adhesion could also be dependent from the above factors and emerge ionic state for example may determine proper signalling and regulates a wide variant of biological functions [6]. Successful osseointegration of biomaterial and proper functioning after orthopaedic and trauma surgery, depends on various surface factors. Different research demonstrate that roughness influenced cell morphology and growth with topography that can change cell orientation and attachment strength. Surface reaction always takes (firstly) water molecule and protein adsorption. At this stage different electrochemical reactions on surface of biomaterial may occur. Following that consideration occurring reaction may lead to the formation of fibrous tissue also results from micromotion of implant or even inflammatory response of human body that ends with the rejection. Proper cellular interaction with surface energy results in cell adhesion, proliferation and differentiation that should lead to matrix production and calcification with expected expand osseointegration. Significance of above relations focused the researchers attention on surface properties without necessity of changing basis. The future of economic processes of surface properties enhancement seems to be high energy treatments employing lasers [7, 8], electron beam or plasma [9]. Problems of modifying więcej » Czytaj za darmo! »

Machine parts and other products exploited in a corrosive environment should be characterized by specified physicochemical properties. Surface layer properties have a decisive influence on corrosion resistance of products. Their enrichment by chemical elements with improved resistance to corrosion (such as chromium) is justified. Diffusion chromizing and galvanic chromizing are the most popular methods [1]. Diffusion chromizing is a heat treatment procedure. Phase composition of diffusion chromized layers is determined by carbon content in the substrate as well as time and temperature of diffusion process. In the case of saturation of the substrate with a carbon content of less than 0.2%, the chromium layer is a solid solution of chromium in the ?ż iron. This solid solution was characterized by increased resistance to water-supply water and sea water. When carbon content in the substrate exceeds 0.2%, it leads to formation of surface layer with zone chromium carbides, which are resistant to wear by friction. In practical applications, diffusion chromizing is applied to steels with a carbide content in the range of 0.7?€1.5% and in the temperature range of 950?€1050?‹C for up to 6 hours. Products after diffusion chromizing can be subjected to different heat treatment procedures, depending on applications and service loads distribution. Diffusion chromizing has a number of applications, like cold metal forming tools, metal casting tools and different machine parts. Galvanic chrome coatings are obtained in the process of electrolytic deposition of chromium on conductive substrate. Galvanic chromium coatings (whit a thickness higher than 25 microns), have a number of advantages: high wear resistance, coefficient of friction lower steel, good thermal conductivity and stability at high temperature. However, these coatings are p więcej » Czytaj za darmo! »

Aluminium is a common alloying addition in many industrially important high temperature alloys, while MgO is either main constituent or sintering aid in advanced refractories used in melting and casting of such alloys. Thus information on reactivity in Al/MgO system is of a great practical importance. Furthermore, knowledge on interaction at the Al/MgO interface is vital for understanding the mechanism of in-situ synthesis of DIMOX (Direct Matrix Oxidation) type composites, i.e. Al-Al2O3 [1, 2]. The early wetting experiments [3?€6] performed in vacuum with Al/MgO system showed that liquid Al reacts with MgO to form inside the substrate a thick reaction product region (RPR). Both its thickness and structure were found to depend on substrate structure (monocrystalline or polycrystalline, crystallographic orientation). Mcevoy et al. [3] suggested the formation of MgAl2O4 inside the RPR, while Fujii and Nakae [4] reported Al2O3. However, the more recent study of the group led by Fujii [5] clearly evidenced that both MgAl2O4 and Al2O3 phases can be formed. Simultaneously, they claimed that the type of alumina formed in RPR depends on the substrate orientation, i.e. ?ż-Al2O3 for (100) MgO and ?Č?Ś- ?Č- and ?Â-Al2O3 for (110) MgO and (111) MgO, respectively. Our experiments involving [100], [110] and [111] MgO substrates showed that in all cases, the reaction starts with the formation of Al2O3 separated by Al channels [6?€8]. Only in later stages, locally the layer composed of MgAl2O4 and Al starts to form as well [6, 7]. The analysis of the electron diffraction patterns acquired from the Al2O3 crystallites indicated that they were always of the same corundum ?ż-Al2O3 type, independently of substrate orientation. The characterization of RPR microstructure in the Al/MgO is as important as phase identification but the former so far gained much less attention. The early investigation performed with the help of optical micros więcej » Czytaj za darmo! »

One of the most important changes in the domain of current surface engineering consists in the discovery and application of modern materials and techniques of the production, as well as their application in nanotechnology, biophysics, optoelectronics and other, dynamically developing field of science and common applications of the technology. Therefore, to produce thin films, which are widely used in the above-mentioned industries the new technology namely pulsed laser deposition (PLD) was applied. Complex Metallic Alloys (CMA) are characterized by the presence of a hundred up to over a thousand atoms in one unit cell. They are exceptional intermetallic phases. The first pioneering work concerning the structure of intermetallic compounds was published by Pauling in 1923 [1]. It was focused on the NaCd2 compound (1152 atoms in a unit cell). There are some other examples of such materials: the Bergman phase: Mg32(Al, Zn)49 (162 atoms in a unit cell) [2], or the Samson phase: ?Ŕ-Al3Mg2 (1168 atoms in a unit cell) [3, 4]. According to Samson, the ?Ŕ-Al3Mg2 phase is a light material (density: 2.2 g/cm3) with exceptionally large unit cells that crystallize in a face centered cubic (FCC) lattice with the crystal lattice parameter a = 2.82 nm. The basic elements and simple intermetallic compounds, compared to CMA materials [5, 6] with giant unit cells, are generally characterized by unit cells consisting of only a single atom or several tens of other atoms. On the other hand, in the giant unit cells that are found in ?Ŕ-Al3Mg2 and that are characterized by lattice parameter values in the order of several nanometers, there is a shift of the crystal lattice at the scale of interatomic distances. In such case, atoms are arranged into polytetrahedral clusters and the structure of CMA materials is characterized by a certain duality, namely: at the nanometric scale, the structure of CMA materials is similar to that of crystals, while at ato więcej » Czytaj za darmo! »

Sn-Zn-Cu alloys can be attractive as a lead-free solder for electric and electronic assembly. They can be a replacement for so far used solders containing toxic lead. The maximum amount of lead in materials is limited by Restriction of Hazardous Substances Directive (ROHS) by European Union from 2006. Among the lead-free solders SAC (tin-silver-copper alloys) and eutectic Sn-Ag alloy are mainly used. They have good physicochemical properties, but they are difficult to obtain by electrodeposition or electroless deposition methods hence pure tin is currently the main material used for deposition of solder layers [1]. Sn-Zn eutectic alloy has been considered as one of the more attractive lead free solder alloys [2]. It is called a new generation alloy [3] and it can be simple obtained by electrodeposition [4?€9]. Sn-Zn eutectic alloy has good mechanical properties, low melting temperature (198.5?‹C) and relatively low cost. Sn-Zn alloys have been received since beginning 20th century as a corrosion protective layer (substitutes for cadmium, more expensive in this time) [4?€9]. Copper, silver, indium, bismuth and several other elements can be used as a third and fourth component of alloy which improve the soldering and mechanical properties [2, 10, 11]. Small addition of Cu can improve properties of these alloys such as a flexural strength, corrosion resistance and it can reduce dezincification of solder [10?€12]. Copper improves also an electrical properties and it can reduce the amount of Zn phase in Sn-Zn eutectic which cause poor oxidation resistance [2]. Electrodeposition can be the best way to obtain Sn-Zn-Cu alloys. Knowledge about receiving Sn-Zn-Cu ternary alloy is limited. The electrodeposited Sn-Zn-Cu layers can have many application (solar cells [18], negative electrode in lithium-ion batteries [14], corrosion resistant layer [13]), but there is no information about obtaining this alloys directly więcej » Czytaj za darmo! »

Friction stir surfacing (FSS) (also known as friction stir processing - FSP) utilizes the same process principles as friction stir welding (FSW). However, instead of joining samples together, FSS modifies the microstructure of surface layers in monolithic specimens to achieve specific and desired properties. As in FSW, the tool induces plastic flow during FSS, but depending on the process parameters, i.e. applied force, tool velocity and rotation speed, the material flow can yield a modified microstructure that is beneficial to the performance of the material. FSS, therefore, is an exciting technique for microstructural development and property enhancement [1, 2]. The mechanical properties of cast aluminum alloys are significantly limited by porosity, coarse acicular silicon phases and coarse aluminum dendrites. These three factors can significantly degrade the fracture toughness and fatigue resistance of the alloy. Various foundry and heat treatment schedules are traditionally employed to modify the aluminum microstructure in order to minimize the impact of these factors. Friction stir surfacing, however, offers the ability to locally modify the microstructure and reduce, in particular, the porosity, thus potentially improving ductility, fracture toughness and fatigue [3, 4]. In the present study, friction stir surfacing was applied to samples of cast aluminum alloy AlSi9Mg. A coupled thermal/material flow model of the process is presented, and the effect of tool velocity and tool rotation speed on the material flow and temperature characteristics of the process is discussed. Experimental procedures Friction stir surfacing was performed utilizing a typical milling machine specifically adapted for the processing trials. The FSS tool was made of HS6-5-2 high speed steel, having a 20 mm diameter shoulder without a pin. The tool tilt angle during processing was held constant at 1.5°. The rotational speed r and tool velocity v vari więcej » Czytaj za darmo! »

For years, metallurgists seek to manufacture structural steel with the highest strength properties while still satisfying low temperature toughness. With the growth of the yield strength it is possible to make the structure of the elements of a smaller wall thickness, and therefore lighter and less expensive to transport. A smaller wall thickness requires less welding consumables and hence the welding process become shorter. The increase in strength properties of steel can be achieved by proper selection of the chemical composition and/or quenching and tempered processes. Such opportunities provide consistently quenched and tempered steels, by the adequately matched the chemical composition and appropriate heat treatment. These steels have very good mechanical properties and good plastic properties with good weldability. The mechanical properties and chemical composition can be found in the standard EN 10025-6 [1]. It should be noted, however, that the steels of yield strength above 1000 MPa are not mentioned in the current standard. This is due to the fact that these steels are a relatively new materials for constructions. An important development has been achieved in ultra-high strength low-alloy steels. The good impact properties is a result of the addition of small amounts of V by causing V4C3 precipitates to form during tempering. The dispersion strengthening by this carbide raises the yield strength while at the same time retards grain growth and improves the impact resistance [2]. The previous investigation have shown that Mo moderately increases the yield strength of martensitic steels, probably due to its large atomic size, whereas the addition of Mn results in a slight decreases in yield strength. Authors [3] reported that the both Mn and Mo increase the stacking fault energy of the austenite matrix, although Mn is generally considered to stabilize the ?Á phase by lowering the stacking fault energy of the austenite. więcej » Czytaj za darmo! »

Nowadays, finding the lead free substitutes for the Pb-high content solder materials for the use at the higher (250÷350°C) temperature [1÷6] as well as development of the new soldering techniques in the electronic industry are of prime importance in the environment friendly technologies. The diffusion soldering is the alternative joining technique which results in the interconnections characterized by the high thermal stability combined with relatively low-temperature of soldering [7÷10]. However, in order to apply this technique in the production line it is necessary to shorten the time to several seconds of soldering process. Recently, number of experiments have been performed in order to find suitable additions which could accelerate the diffusion during the soldering process [11, 12]. The presence of the Ni addition, even in very small amount (~5 at. %), in the Cu pads caused the suppression of the Cu3Sn phase formation in the reaction zone at substrate/solder interface. Additionally, the nickel significantly changed the morphology of the Cu6Sn5 intermetallic compound growing in the joints and which was even more important increased the rate of its formation. However, some discontinuities were present in the centre of the interconnections (for example Fig. 1d in Ref. [13]). The same problem was reported by Chung et al. [14] in the case of Cu/Sn/Cu/Sn/Ni diffusion couples aged at 200°C for different times. The discontinuities are described as the ‘‘Kirkendall voiding’’. Their occurrence is caused by the agglomeration of excess vacancies as the result of the different intrinsic diffusivities of Cu and Sn in the forming intermetallic phase [15]. The amount of Sn diffusing across the (Cu, Ni)6Sn5 phase is more than Cu [16]. It is also known that the voids are mostly generated within Cu3Sn layer, but rarely within the Cu6Sn5 layer [17÷23]. However the lack of Cu3Sn phase in our previous studies [13] was więcej » Czytaj za darmo! »

In technologies of production of self-greasing bearings the porous framework is saturated with a liquid grease or grease material particles are introduced in the base powder. PM bronze or iron is used as material for bearing bases made with the use of powder metallurgy method [1]. The PM bronze sintering kinetics was described in paper [2]. A special group of bearings are bearings operating under increased temperature. They require special hard greases suitable for such conditions and resistant to oxidation. Results obtained on steel sinters [3] indicate that solid grease mixtures composed of microparticles and nanoparticles in the quantity of 7?€15% and size of 50?€200 nm constitute an effective grease both under the ambient temperature and increased temperature. The grease is introduced, with the use of a pressure method, in the form of a solid grease suspension into the porous structure of the sinter, which leads to a formation of a thin layer of grease film on the internal surface of the sleeve [4, 5]. Paper [6] presents the results of tests on bronze sinters to be used for bearings. The influence of unit pressing pressure on the density, mechanical properties of bronze sinters and surface morphology has also been developed. This paper specifies the sinter properties in the form of sleeves for infiltration with the use of MoS2 nanoparticles assuming parameters of their production specified in the paper [6]. OBJECTIVE The objective of the test included the assessment of the surface condition and mechanical properties of sleeves made of PM bronze after such operations as sintering, calibration and calibration with densification. The tests made on the sleeve included: .. determination of the density depending on the technological process conducted, .. observation of the surface condition with the use of a scanning electron microscope (SEM), .. tests on mechanical properties of sleeve during a technological comp więcej » Czytaj za darmo! »