Friction-wear properties of a Co-29 mass%Cr-6 mass%Mo alloy (ASTM F799-95) but reducing the amount of nickel were evaluated with friction-wear test using a pin-on-flat type reciprocating friction tester in air and phosphate buffered saline, PBS(À), as a quasi-biological environment under applied stress of 1.0, 3.5 and 5.0 MPa to understand the performance of this alloy for metal-on-metal type artificial hip joints. In addition, metal ions dissolved in PBS(À) after the test was quantified. As a result, wear loss in PBS(À) is much smaller than that in air and increases with the increase of applied stress in both air and PBS(À), while the coefficient of friction in steady state during the test is larger in PBS(À) than in air, according to lubrication behavior of wear debris and PBS(À). Wear damage in PBS(À) is smaller than that in air, however more small scale of irregularity is observed in PBS(À) than that in air. Nickel and molybdenum are preferentially dissolved during the test.

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We have already developed a novel -type titanium alloy, Ti-8Fe-8Ta-4Zr, for biomedical applications. Ti-8Fe-8Ta-4Zr showed higher strength than conventional biomedical titanium alloys, such as Ti-6Al-4V ELI, Ti-6Al-7Nb, and Ti-13Nb-13Zr. In addition, the alloy also showed higher corrosion resistance than cp-Ti and Ti-6Al-4V ELI in Hanks' solution. In particular, the breakdown potential of the alloy (the pitting potential) was over 3.5 V vs. SCE (saturated calomel electrode) and much higher than those of cp-Ti and Ti-6Al-4V ELI. A slightly active region was observed at about 1.7 V vs. SCE that may be related to the high breakdown potential.In this study, the surface oxide films on Ti-8Fe-8Ta-4Zr after anodic polarization at 1 and 3 V in Hanks' solution were characterized using X-ray photoelectron spectroscopy and Auger electron spectroscopy to elucidate the high corrosion resistance mechanism of the alloy in Hanks' solution. In addition, the surface oxide film on the alloy before anodic polarization was also characterized for comparison.The surface oxide film on Ti-8Fe-8Ta-4Zr is grown with anodic polarization. Calcium phosphate is formed on the alloy after polarization. The corrosion resistance of the alloy after polarization at a potential above 1.7 V is improved by the concentration of iron and titanium in the surface oxide film. A titanium hyper-oxidized layer with a low iron concentration is observed within the surface oxide film. This layer is generated with polarization and worked as a corrosion-protective layer. The slight active region on the polarization curve may be caused by the dissolution of iron and titanium.