Friction-wear properties of nickel-free Co-Cr-Mo alloy in a simulated body fluid

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(-), 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(-) after the test was quantified. As a result, wear loss in PBS(-) is much smaller than that in air and increases with the increase of applied stress in both air and PBS(-), while the coefficient of friction in steady state during the test is larger in PBS(-) than in air, according to lubrication behavior of wear debris and PBS(-). Wear damage in PBS(-) is smaller than that in air, however more small scale of irregularity is observed in PBS(-) than that in air. Nickel and molybdenum are preferentially dissolved during the test.