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Corrosion resistance of sintered AISI 316L-hydroxyapatite biomaterials in Ringer's solution DOI:10.15199/28.2018.1.4

  The lengthening of human lifetime, diseases of old age, increase in the number of accidents increase the demand in implants and significant progress in the medicine and bioengineering of materials results in an enlargement of the biomaterials application area in medicine [1]. Many years of clinical experiences have shown that biomaterials must meet quite high and varied requirements including biocompatibility, but also excellent mechanical properties, corrosion resistance, wear resistance and suitable technological properties [1÷17]. Generally, surgical and also dental implants are made of metals, especially austenitic stainless steels and titanium alloys [1÷29]. Austenitic stainless steels were the earliest adapted for implantation in the human body. They exhibit high mechanical properties, relatively good corrosion resistance and at the same time a low production cost and availability. However, austenitic stainless steels are particularly susceptible to destruction due to the rather high tendency to naturally self-passivate (e.g. in comparison to titanium alloys) and a strong susceptibility to electrochemical corrosion in the environment of body fluids [1, 5, 10, 11, 14÷18, 23, 30]. Moreover, the products of corrosion get to the surrounding tissues and may cause the occurrence of allergic reactions, inflammations or metallosis [3]. Ceramic biomaterials have been arousing the special interest among scientists for a long time. It can be stated that hydroxyapatite (HA) is one of the most investigated bioceramics [2, 31÷38]. Besides mineral origin hydroxyapatite occurring for example in igneous rocks, metamorphic limestone or phosphate sedimentary rocks, there is also a natural hydroxyapatite (mainly in the bones and teeth of vertebrates) and a synthetic hydroxyapatite. The synthetic hydroxyapatite does not exhibit complete biocompatibility with the human bone and teeth and also it is relatively expensive material. That is why [...]

Application of image analysis to porosity investigation into sintered copperalloying AISI 410L stainless steels

  It is known that stainless steels are one of the most important group of materials. Their importance is confirmed by the range of applications - products made of stainless steels. Currently steady growth of demand for stainless steels can be noticed [1], also for produced by powder metallurgy technology. Nowadays there are hundreds grades of commercially available stainless steels [2]. Many of them can be manufactured by using conventional water atomization powder and press and sinter processes. Powder metallurgy provides considerable opportunities to obtain a wide range of properties and corrosion resistance in sintered stainless steels. There are a lot of applications which required the stainless steels with high strength and good corrosion resistance. In the case of high strength and hardness requirements, graphite addition can be introduced to AISI 410L or more highly alloyed materials, such as precipitation hardening stainless steel, where 17-4 PH grade can be applied. The use of increased levels of alloying elements in sintered stainless steels (produced by powder metallurgy) is both costly and counter-productive due to the negative effect on compressibility. Graphite is added to ferritic grade of steel to promote formation of martensite. Usage of graphite addition into AISI 410L powder increases the strength and hardness of sintered steel. Beside, AISI 410L powder with graphite addition has high compressibility, so the sintered density of this material is also high and properties are satisfactory. But, on the other hand, graphite addition requires strict control of atmosphere in sintering furnace in order to achieve consistent carbon levels. Disadvantage of graphite usage is also its negative influence on corrosion resistant of stainless steels [2÷5]. In this case, introduction of copper to the AISI 410L stainless steel is an alternative solution. Copper increases corrosion resistance, while providing solid solution st[...]

The influence of aging temperature on corrosion resistance of sintered 17-4 PH stainless steel DOI:10.15199/28.2016.2.3

  Among the precipitation hardening stainless steels, martensitic grade of 17-4 PH has a special importance. This steel exhibits a good combination of high mechanical properties and good corrosion resistance. Therefore it is widely used in many branches of industry. The pitting corrosion behaviour of sintered 17-4 PH steel processed under different aging processing conditions in 0.5 M NaCl solution at 25°C was studied by open circuit potential measurement and potentiodynamic polarization technique. Compared with the sintered 17-4 PH, the corrosion resistance of the solution treated and aged steels were improved, as evidenced by a noble shift in open circuit potential, a higher pitting potential, a higher polarization resistance and a lower passive current density. Considering the influence of aging temperature on the pitting behavior of the 17-4 PH steel, it can be concluded that steel aged at 480°C exhibited the highest corrosion resistance in 0.5 M NaCl solution. While aging treatment at 500°C resulted in the worst corrosion resistance. In addition, the hardness of the solution treated and aged 17-4 PH was higher than that of the sintered steel. Key words: 17-4 PH stainless steel, pitting corrosion, hardness.1. INTRODUCTION It is known that the corrosion destruction is one of the main sources of material loss. And furthermore it contributes to the pollution of the environment and even constitutes a risk to human health. The problem of materials durability in natural and artificial environments is extremely important from the viewpoint of design and also application of constructions, devices, tools and etc. The degradation of the materials and the environment as a result of corrosion can be effectively reduced by appropriate prevention, mainly by using methods of anticorrosive protection and adequate selection of materials. The steels containing at least 10.5 wt % chromium and other elements (such as nickel or molybdenum) are more resist[...]

Wpływ temperatury starzenia na odporność na korozję wżerową spiekanej stali nierdzewnej 17-4 PH DOI:10.15199/28.2016.2.3

  1. INTRODUCTION Titanium is characterized by high corrosion resistance and great strength. Therefore, this material is often used in chemical, petrochemical, power, aircraft or pharmaceutical industry. Because of high costs, titanium is only spread in the form of a thin layer which is laid on the base material in the process of explosive welding. While cladding, the base material and titanium collide with a great velocity of about 2000÷3500 m/s [1]. As a result of the collision, the materials bond strengthening mainly the area of their joint. The process results in: generating additional stresses in both materials, changing the density and material structure, and increasing hardness. In order to eliminate the changes created in the process of welding i.e. the stresses, the formed bimetal is subject to heat treatment which consists in stress relief annealing. The selection of the temperature level, and the time of heating and annealing of the formed bimetal are aspects that need consideration since they are hindered by various properties of the used materials. This paper [2] discusses the above mentioned issue. The paper [3] presents a description of a bimetal consisting of steel as a base material and titanium as a overlaid material (layer), with a substantially thick interlayer between the joined materials. According to the conducted literature review, the processes of explosion welding were studied by the authors of the works [1, 4÷6]. They described the detonation velocity as well as the generated high pressure which accompany explosion welding. Moreover, the paper [4] presents the results of hardness tests for cladding configurations for sheets arranged at various angles. The paper [5] discusses the method of calculation and selection of explosive material parameters for various thicknesses of the cladded materials. The paper [6] involves detailed information on explosion welding itself. The process of welding and the phen[...]

Badania zagęszczania proszku stali nierdzewnej 17-4 PH podczas spiekania w próżni i w wodorze

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Stale nierdzewne utwardzane wydzieleniowo są stalami o małej zawartości węgla, których utwardzenie osiąga się przez kombinację przemiany martenzytycznej i utwardzenia wydzieleniowego stosunkowo miękkiego, niskowęglowego martenzytu [1]. Ostatnio można zauważyć wyraźne rozszerzenie wykorzystania metod metalurgii proszków do produkcji elementów ze stali nierdzewnych. Przewaga metalurgii proszków w zakresie produkcji wyrobów ze stali nierdzewnych nad innymi metodami polega na możliwości dostarczenia metalowych wyrobów o właściwościach regulowanych w wyjątkowo szerokim zakresie, co pozwala dobrze dopasować produkowany wyrób do wymagań dyktowanych warunkami jego pracy. W odniesieniu do stali nierdzewnych może się to sprowadzić do projektowania właściwości mechanicznych, chemicznych, magnetycznych i także geometrycznych (wielkość i rozmieszczenie porowatości) tych materiałów. Spieki ze stali nierdzewnych należą do produktów o dużej wartości dodanej i wykazują równocześnie dużą uniwersalność, gdyż mogą zaspokajać wiele potrzeb i tym samym być stosowane do wielu celów. Zawdzięczają to cennym właściwościom materiału: odporności na korozję (także w podwyższonej temperaturze), bierności chemicznej wobec środków spożywczych i środowiska organizmów żywych, wysokiej wytrzymałości, dobrej plastyczności, wysokiej odporności na zużycie, zachowania korzystnych właściwości zarówno w podwyższonej temperaturze, jak i w warunkach kriogenicznych, podatności do spajania i zdolności do recyklingu. W Polsce zakres produkcji takich wyrobów jest bardzo ograniczony, m.in. z powodu braku odpowiednich doświadczeń w zakładach metalurgii proszków w zakresie przetwarzania wymagających i drogich surowców, jakimi są proszki stali nierdzewnych. Stosunkowo nowym kierunkiem rozwoju spiekanych materiałów ze stali nierdzewnych jest wykorzystanie takich składów tych stali, by były one zdolne do obróbki cieplnej polegającej na utwardzaniu wydzieleniowym. W ten sposób [...]

Solidification process of sintered AISI 316L austenitic stainless steel powder modified with boron-containing master alloy

  Wrought stainless steels have wide range of applications as consequence of their corrosion resistance in aggressive environments. Powder metallurgy (P/M) technology can increase range of application of stainless steel through significant reduction of manufacturing costs by simplifying production process. Unfortunately, manufacturing by P/M process created, in structure component, undesired porosity which greatly reduces corrosive resistance of sintered steel. A reduced open porosity can be usually attained by forging or other mechanical treatment. Of course such an operations increase costs. In order to keep manufacturing costs on reasonable level, it is desired to eliminate porosity during already existing manufacturing process. One of the possibilities is proper chemical modification of base alloy to induce appearance of liquid phase during sintering in order to achieve high density sinter. Many researchers indicated boron as an excellent activator for sintering ferrous alloys. Boron added to iron creates lowmelting eutectic liquid (1177°C) which activates densification mechanisms: (i) particles rearrangement by decreasing friction forces among the particles, (ii) fragmentation of particles by liquid penetrating grain boundaries. Moreover, presence of eutectic liquid in some cases under specific conditions during sintering process may lead to appearance of non-porous superficial layer. Such a layer is characterized by the lack of solidified eutectic liquid what greatly improves corrosive resistance of sinter by eliminating electrochemical corrosion cells. The creation of nonporous superficial layer usually requires addition of the high amounts of boron (higher or equal to 0.4 wt %) which during cooling solidifies as a brittle eutectic on grain boundaries drastically lowering mechanical properties of sinter [1]. Loss occurs especially when solidified liquid creates the continuous network surrounding grains [2]. Dispersing of [...]

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