1. CEL PRACY Celem pracy jest określenie charakteru uszkodzeń powierzchni wkładki endoprotezy stawu kolanowego wykonanej z PE-UHMW usuniętej reoperacyjnie z powodu obluzowania aseptycznego po 13 miesiącach użytkowania z wykorzystaniem nowoczesnych technik badania powierzchni materiału. 2. MATERIAŁ I METODYKA BADAŃ Przedmiotem badań była częściowo związana endoproteza stawu kolanowego (rys. 1) usunięta reoperacyjnie z powodu obluzowania aseptycznego po 13 miesiącach użytkowania. W celu przestrzennego odtworzenia kształtu powierzchni roboczej wkładki endoprotezy została ona zeskanowana za pomocą skanera SMARTTECH 3D. Ponieważ rozpraszająca promienie świetlne powierzchnia polietylen więcej »

This work focuses on the influence of creep phenomenon on the cast IN713C nickel-based superalloy. The carrot-shape IN713C superalloy castings were produced in an investment casting cluster mould and the creep test samples were then prepared from the castings. The creep tests were carried out in order to investigate processing-microstructure-property relationships. The resultant macro- and microstructures were observed and characterized after the creep tests using light microscopy, scanning electron microscopy and scanning transmission electron microscopy. The aim of the analysis was to reveal the changes in the microstructure that occurred as a result of the creep and to identify the phases that participate in voids formation, and crack generation and propagation during the creep tests. It was confirmed that the creep resistance of the IN713C superalloy is negatively affected by some structural characteristics such as porosity, (γ + γ′) eutectic or carbide precipitates along the grain boundaries. Our work confirms that a combination of thermal conditions with a tensile force affected the microstructure of IN713C nickel-based superalloy causing changes in morphologies of the existing precipitations and phase transformations, as in the case of the carbides. Additionally, carbide sulphides containing primarily Zr and intermetallic phase including mainly Ni and Zr were observed. Key words: IN713C, superalloy, creep, microstructure.1. INTRODUCTION Creep, fatigue and the interaction between them play important roles in determining the lifetime of many device components used at elevated temperature. Turbine blades made of nickel-based superalloys are subjected to complex thermal and mechanical creep and fatigue loads [1, 2], resulting in a marked change in microstructure during creep as the originally cubic morphology of the γ′ precipitates becomes directionally coarsened (raft-like) perpendicular to the direction of t więcej »

1. CEL PRACY Artykuł dotyczy wpływu zjawiska pełzania na strukturę odlewniczego nadstopu na osnowie niklu IN713C. Makro- i mikrostrukturę materiału uzyskaną w efekcie przeprowadzonej próby pełzania obserwowano przy różnych powiększeniach. Celem badań było ujawnienie zmian struktury, jakie pojawiły się w efekcie pełzania i zidentyfikowanie faz, które brały udział w powstawaniu nieciągłości materiału oraz generowaniu i propagacji pęknięć podczas próby pełzania. 2. MATERIAŁ I METODYKA BADAŃ Materiałem przeznaczonym do badań był nadstop IN713C na osnowie niklu. Dzięki niskiej cenie, dobrej lejności, stabilności mikrostruktury i właściwościom mechanicznym w wysokiej temperaturze IN713C jest stosowany do odlewania łopatek turbin niskiego ciśnienia. Na ry więcej »

The basic process for manufacturing of aircraft engine hot section elements made of nickel-based superalloys is investment casting using multilayer ceramic shell moulds. Introduction of new engines designs with higher thrust, lower fuel consumption and lower noise emissions enforce continual modification of casting materials, models, ceramic moulds, including melting, pouring and heat treatment processes parameters. The aim of this study was to determine the effect of pouring temperature and cobalt aluminate modifier in the subsurface layer of the mould on macrostructure of the IN 713C castings. The size of misruns, chill, columnar and equiaxed zones on the surface of the wedge castings is most affected by pouring temperature. Additionally it was proved that cobalt aluminate is an effective modifier of the IN713C superalloy causing not only refinement of equiaxed grains, but also reduction in the columnar grain size fraction. Key words: investment casting, superalloys, microstructure, grain size, dendrite arm spacing.1. INTRODUCTION IN 713C superalloy in as-cast state is mainly used, among others, for aircraft engine components. These elements are casted using the lost-wax method with multilayer ceramic moulds. Casted gas turbine blades are characterised by coarse grains of heterogeneous microstructure. The casting often does not meet mechanical properties required from the kinds of elements used in the aerospace industry [1, 2]. The microstructure improvement of nickel-based superalloy blades may be obtained by appropriate shaping of grains size during the casting process [3, 4]. Controlled grain size can be achieved by specific pouring temperature, mould temperature, and the use of modifier in the surface layer of the mould [5, 6]. Highest grain refinement of nickel-based superalloys was obtained with application of cobalt aluminate modifier [7, 8]. The aim of presented study was to determine the effect of pouring temperature and Co więcej »

In this paper the review of literature data concerning preparation, properties and applications of Reticulated Vitreous Carbon (RVC) is presented. Vitreous carbon is a kind of carbon material with specific structure which deviates from crystalline structure of graphite as it has various defects of graphene layers (gaps, five-part rings, interstitial atoms or hetero-atoms substituted instead of carbon atoms) without mutual orientation and fixed distance between layers. Such structure is called “turbostratic" and it is characteristic for materials obtained through carbonization (pyrolysis) of organic substances, usually organic polymers. Because of the orientation level of the packages of graphene layers, vitreous carbon, including RVC, belongs to the group of materials which do not graphitize at high temperature. Type of defects in vitreous carbon structure depends mostly on the choice of precursor material, its preparation and type and method of its processing. In this paper some examples of the most frequently used RVC precursors (e.g. furfuryl resin, phenol-formaldehyde resin) and the methods of RVC preparation starting from the basic framework that is the 100% open-cell polyurethane foam (so called “reticulated foam"). Methods of restructuring the standard commercial polyurethane foam to get the reticulated foam suitable for RVC preparation (i.e. reticulation" methods) are described. The process of impregnation of reticulated foam thus obtained with resins and curing the resulting composite as well as stages of thermal processing leading to carbonization are also discussed. Due to specific properties (high specific surface, thermal and electrical conductivity and good mechanical strength) RVC is presently applied in electrochemistry, medicine or metallurgy. Other forms of vitreous carbons comprise Monolithic Vitreous Carbon (MVC) and Cellular Vitreous Carbon (CVC) — the latter can be applied as sound-absorbing material. Ke więcej »

W artykule przedstawiono przegląd danych literaturowych dotyczących otrzymywania, właściwości i zastosowania retykulowanego węgla szklistego (Reticulated Vitreous Carbon — RVC, węgiel szklisty o strukturze szkieletowej). Węgiel szklisty to materiał węglowy o specyficznej strukturze wykazującej odchylenia od krystalicznej struktury grafitu, w postaci warstw grafenowych zdefektowanych przez występowanie luk, pierścieni pięcioczłonowych, atomów międzywęzłowych i heteroatomów, bez wzajemnej orientacji oraz ustalonej odległości od siebie. Strukturę tę określa się mianem "turbostratycznej" i jest ona typowa dla materiałów otrzymywanych na drodze karbonizacji (pirolizy) substancji organicznych, zazwyczaj polimerów organicznych. Ze względu na poziom orientacji pakietów warstw grafenowych węgiel szklisty, także retykulowany, należy do materiałów niegrafityzujących w wysokiej temperaturze. Pakiety warstw grafenowych w tych materiałach mają mały rozmiar i dowolną orien więcej »

Providing of joint prostheses with high reliability is particularly important because the loss of their functional properties may cause invasive surgery revision. The main exploitation problems with prostheses are loosening (septic or aseptic) and the wear of inserts made of UHMWPE. Identification of the types and mechanisms of cooperating surfaces wear of the knee prostheses affects the improvement of materials selection, design and increase their reliability and durability. Typical kinds of damage of UHMWPE element of the prosthesis include abrasive wear, plastic deformation and creep, fatigue wear (pitting), changing the chemical composition and colour, changing in the structure, cracking. This paper presents the test results of the UHMWPE insert surface of the knee replacement which was used by the patient for 13 months. Microscopic studies, pulse thermography and 3D scanning of the UHMWPE insert were carried out. 3D scanning element has paved the way for reconstruction of the shape of the working surface of the insert of prosthesis. Surface defects in the tested insert were revealed by using innovative methods of pulsed thermography. In order to identify defects, located on the surface, microscopic studies were carried out. They have shown a complex mechanism of wear. Many signs of abrasive wear, fatigue wear (pitting) and microcracks have been observed. Analysis of the bio-bearing operation also indicates the signs of early fatigue wear. The causes of wear of tested elements include too high load applied exceeding several times the weight of the human body, closed space in which products of friction are accumulated. Key words: knee replacement, wear mechanisms, ultra-high molecular weight polyethylene.1. INTRODUCTION The knee joint is the most often undergoing traumatic damage and is the most susceptible to the occurrence of various types of pathologies in the human body. A deformation of the joint is caused by a degenerative disease a więcej »

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 więcej »

1. CEL PRACY Nadstop niklu IN 713C jest stosowany między innymi na łopatki turbin silników lotniczych, odlewane precyzyjnie metodą traconego wosku w wielowarstwowych formach ceramicznych. Łopatki turbin często charakteryzują się gruboziarnistą i niejednorodną strukturą, która nie spełnia rygorystycznych wymagań dotyczących części wykorzystywanych w przemyśle lotniczym. Poprawę struktury łopatek wytworzonych z nadstopów niklu można uzyskać w wyniku odpowiedniego kształtowania wielkości ziarna w procesie odlewania. Ziarna o kontrolowanych rozmiarach można otrzymać dzięki odpowiedniej temperaturze zalewania, temperaturze formy i zastosowaniu modyfikatora w powierzchniowej więcej »

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 więcej »