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This article is a review of important material requirements for hip biomaterials including their response to the body environment (biocompatibility), mechanical properties, wear resistance, fretting corrosion and availability as well as the price. The application of proper biomaterials for hip implants is one of the major focal points in this article. Background information is also provided on metals used in other prosthetic devices and implant components. Titanium and its alloys, cobalt base alloys and stainless steels (bio-steels) are used for load-bearing hip implants. These three groups of metallic materials will be introduced and discussed in detail. Metals and their alloys are crystalline materials since their properties depend on the crystal lattice, chemical and phase compositions, grain size, lattice defects, crystalline texture and residual microand macro-stresses. All these features of biomaterials are formed during technological manufacturing, such as metallurgical process, solidification, plastic deformation (rolling and forging), machining, heat treatment and coating. All these technological processes work in optimal conditions in order to achieve the optimal microstructure and mechanical, chemical and biological properties. Amongst the above-mentioned particular properties of biomaterials, fretting is a major concern as regards hip implants at the femoral head and neck taper interface. Additional important mechanisms of interaction between the implant and the human body must be taken into account, i.e. diffusion stream of foreign particles and atoms from the implant to body fluids, to the tissue and to the bone. These foreign particles and atoms are released from the implant to the body fluid, to the tissue and to the bone as wear product during use. All together they contribute to the wear, i.e. loss of weight, strength or volume of hip components. Wear rates of ultrahigh molecular weight polyethylene mated against Ti-6Al-4V are significantly greater than the ones for Co-Cr-Mo alloys. Therefore, thermochemical surface treatments like diffusion ion nitriding should be applied to increase the resistance of titanium alloys to wear. Austenitic stainless steels are also used for temporary applications, but they have lower resistance to pitting corrosion than titanium and cobalt alloys. The purpose of the paper is to introduce a group of metallic materials, which is often chosen for surgical hip implants. Conclusions of the paper refer to information which support important medical and patient decisions on hip implants. Also, the development of biomaterials, their treatments, properties, surface layers and coatings are considered. All these features develop over time and need synergy and experience in the progress of the biomedical, mechanical and materials science.
Content available remote Failure analysis of the exhaust valve face in diesel marine engine
The exhaust valve from marine diesel engine which was damaged after 2000 hours of service was investigated. In order to prolong the service time the valve face was cladded with cobalt base alloy using laser technique. After failure microstructural and chemical analyses reviled that cladding process was conducted improperly. The chemical composition of the clad layer was far from the designed one and what more completely inhomogeneous. As a result the valve presented different properties in different regions which led to premature failure.
The cobalt base laser cladding layers were investigated after two years of service in two laboratory diesel engines. The microstructures of the clads after service did not demonstrated serious degradation process. Chemical compositions of the used layers and changes in hardness were described. These sorts of layers are suitable for long time service with out substantial damages.
Content available remote Oxidation and exhaust gas corrosion resistance of the cobalt base clad layers
Purpose: Purpose of this work is describing the behaviour of the cobalt base cladding layers after treatment in hot air (750° C, 200 hours) and exhaust gases (700° C, two month). Design/methodology/approach: The layers were produced by two cladding, laser and PTA, cladding technique. Cladding was conducted with a high power diode laser HDPL ROFIN SINAR DL 020 and Plasma Transformed Arc method. The layers consisted of three multitracking sublayers. The cobalt base layers were evaluated by microstructure investigations (optical and scanning electron microscope SEM), chemical analysis and micro hardness measurements. Findings: The microstructure of the investigated layers did not change much, neither on the top part nor in the clad/steel interface after treatment in both environments. On the outer surfaces the oxide layers were observed which consisted generally of chromium and iron oxides. The compositions of this scales were reviled by the EDS analyze. The changes in chemical compositions before and after oxidation and after corrosion in exhaust gases in the dendritic regions and micro regions were confirmed by the semi-quantitative chemical analysis (EDS). Neither the oxidation nor exposition for two month in exhaust gases did not influence on the morphology of the clad layers in any region however changes in chemical composition were observed. For both sort of clads the oxide layers were observed on the surface. The proposed layers are resistant for the hot exhausted gases. Research limitations/implications: The future researches should be done on microstructural and kinetic analyze of high temperature corrosion for higher temperature and times of the process. Practical implications: The clad layers, of this composition, were designed as a method to prolong service time for the ship engine exhausted valve and after this investigation the first valve heads with laser clad layer were installed in working ship engine. Originality/value: The chemical composition of the powder was new one. Also using the laser cladding technique for ship engine parts subject of interesting.
Content available remote Effects of the Time and Temperature on the Oxide Scale Formed on the Cobalt Alloys
The cobalt base PTA (Plasma Transferred Arc) clad layers were investigated under different temperature and time of oxidation. The microstructure of the clads after oxidation demonstrated degradation process which led to the decomposition of the dendrite boundaries. Chemical compositions of the formed scales were depending on the oxidation temperature, chemical composition of the alloy, especially small addition of the silicon, and time of the exposition.
W artykule przedstawiono wyniki badań wpływu obróbki cieplnej na własności elektryczne i magnetyczne szkła metalicznego typu AEM (Co68Fe4Mo1,5Si13,5B13). Omówiono zmiany rezystywności, natężenia koercji, pozostałości magnetycznej i przenikalności magnetycznej maksymalnej stopu w stanie bezpośrednio po odlaniu i po wygrzewaniu w zakresie temperatury od 100 do 400 stopni Celsjusza w czasie 1-64 godzin.
The paper presents the results of investigations concerning the effect of heat treatment on the electric and magnetic properties of metallic glass of the AEM type (Co68Fe4Mo1,5Si13,5B13). The paper also deals with changes of the resistivity, intensity of the coersive force, residual flux density and maximum magnetic permeability of the alloy immediately after casting and soaking 1-64 hours within the temperature range from 100 to 400 degrees centigrade.
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