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Abstract: The tribological behavior of sintered aluminum metal matrix composites (MMCs) containing various volume fractions of particles made of complex metallic alloys (CMAs) was investigated in a reciprocating dry sliding tribo-tester operated in ambient air against 10mm diameter Al2O3 balls. The Al-based MMCs tested contained either 15μm size AlCuFeB or 25μm size AlCuFeCr-particles. An improvement in the dry sliding wear resistance of aluminum was achieved by the incorporation of these CMA-particles acting as a second phase reinforcement. The wear resistance depends on the volume fraction of CMA-particles but not on their composition, nano-hardness or size. These Al-based MMCs containing CMA-particles exhibit however a higher coefficient of friction than pure aluminum under dry sliding against a ceramic counterbody. A clear correlation was not found between composition, nano-hardness, size or volume percent of CMA-particles, and coefficient of friction. The dominant wear mechanisms active on MMCs containing either AlCuFeB or AlCuFeCr-particles are abrasion and adhesion, but abrasion dominates in the case of Al-MMCs containing AlCuFeCr-particles. [Copyright &y& Elsevier]

Abstract: Solid-state deformation of UHMWPE used in total joint prosthesis could be a relevant treatment prior to cross-linking to obtain high strength. However, little is known about the influence of chain alignment (texture) on sliding wear behavior. In this work, we analyzed i) the deformation mechanisms of UHMWPE resulting from a uniaxial tension (elongation of about 300%) and ii) the influence of the texture on the friction behavior resulting from ball-on-flat sliding tests (reciprocating sliding mode). Microstructural investigations show that tension induces a transformation of the initial lamellar morphology into specific microfibrillar morphology. White light interferometer (WLI) studies show that texturing causes an increase of the roughness by a factor of about two. After 50,000 sliding cycles, the cumulative dissipated energy decreases from 109,300–103,600μJ for untreated UHMWPE to 64,600 and 43,150μJ for textured UHMWPE, parallel and perpendicular to the texture direction, respectively. Considering that wear resistance increases with decreasing dissipated energy, textured UHMWPE may have anti-wear properties. However, cracks are noted at microscopic scale for textured UHMWPE. Regarding wear resistance, such defects are not suitable and can be avoided by reducing the roughness of textured UHMWPE prior to wear tests. [Copyright &y& Elsevier]

Abstract: The combined corrosion-wear degradation of nano-structured Ni–SiC coatings in sliding contacts immersed in electrically conductive solutions is investigated in situ by electrochemical techniques (open-circuit potential measurements, E OC, the potentiodynamic polarization measurements, PD, and the electrochemical impedance spectroscopy). The coating thickness was 50μm, with an average volume of dispersed phases inside nickel of 20%. The samples were tested in a cell, containing the electrolyte and electrodes, and mounted on a pin-on-disk tribometer, with the working surface of the specimen facing upwards. Both continuous and intermittent friction tests were carried out. In the intermittent tests, friction was applied periodically: during each cycle, friction was first applied for 2s at constant sliding speed under constant normal load and then stopped during a latency time of 20s or 0.5s. Without friction, the free potential reaches a passive value after immersion in the test solution. When friction force is applied the free potential is shutting down to active values. Under friction the measured current, I can be considered as the sum of two partial currents: one generated by the wear track areas, where the passive film is destroyed and the surface is active; the other one linked to the surface not subjected to friction and that remains in the passive state. A localised corrosion process when subjected to friction in 0.5M K2SO4 was not observed on nano-structured Ni–SiC composite coatings. The mechanical destruction of the passive film occurs in the wear track by friction and subsequent restoration of the film (repassivation) when friction stops. The wear volume loss increases with sliding forces. [Copyright &y& Elsevier]

MoSx coatings were prepared with an unbalanced DC magnetron-sputtering system by varying the DC power mode, target type and liquid nitrogen trap. The composition and surface morphology were examined by energy dispersive X-ray and scanning electron microscopy; structural characterization was determined by X-ray diffraction. The friction and wear properties were evaluated with a fretting tester in dry (<10% relative humidity) and humid (50% and 90% relative humidity) air. MoSx coatings deposited by simple DC power tended to form rougher surfaces, and had a higher edge orientation of crystallites with worse tribological performance than those by bipolar pulsed DC power. MoSx coatings made by a cold pressed target had a lower deposition rate, and were inclined to form (002) basal orientations parallel to the surface especially at higher argon pressures. The contents of oxygen and carbon in the MoSx coating with the use of liquid nitrogen trap were greatly reduced, but MoSx coatings had lower coefficients of friction and shorter wear life at higher relative humidity. The role of these deposition variables in the formation process is discussed. [Copyright &y& Elsevier]