2005 Volume 46 Issue 7 Pages 1593-1596
Nitrogen ions were implanted in a Co–29 mass%Cr–6 mass%Mo alloy (ASTM F799-95) with reducing the amount of nickel in order to improve the friction-wear properties. The friction-wear properties of unimplanted and nitrogen-ion-implanted Co–Cr–Mo alloys were evaluated 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 3.54 MPa to understand the performance of this alloy for metal-on-metal-type artificial hip joints. As a result, the wear loss in PBS(−) was much smaller than that in air and increased with the increase of applied stress in both air and PBS(−), while the friction coefficient in a steady state during the test was larger in PBS(−) than in air, according to the lubrication behaviors of wear debris and PBS(−). Nitrogen-ion implantation is effective to decrease the friction coefficient in PBS(−) at the sliding interface between mutual Co–Cr–Mo alloys as well as to decrease the wear debris in PBS(−). Both in air and PBS(−), the surface of a N2+-implanted flat specimen was smoother than that of an unimplanted flat specimen. Cobalt phosphate was precipitated as a corrosion product on the pin during the friction-wear test.
