Friction and Wear Characteristics of Surface-Modified Titanium Alloy for Metal-on-Metal Hip Joint Bearing

Cobalt-chromium-molybdenum bearing materials have excellent wear resistance, but due to the cytotoxicity issue of chromium ions, they need to be replaced with biocompatible metal materials. Titanium alloy is a biocompatible material, and is used as a stem and acetabular shell of a hip joint. However, titanium alloy is not used as a bearing material because its wear resistance is poor. Therefore, in order to evaluate the applicability of titanium alloys for metal on metal bearing combinations, surface modification was performed in three methods. Surface modification by surface texturing, thermal oxidation, and thermal oxidation - surface texturing was performed on one side of the friction pair. Thermally oxidized-textured titanium surface showed the best friction and wear characteristics as the bearing surface. The friction decreased by 62% and the wear resistance increased by up to 300 times compared with the other combinations. This was due to two causes. First, the formation of an oxide layer onto the surface of the dimpled titanium resulted in reduced occurrence of adhesive wearing, and the plastic deformation of the edge of the dimple is suppressed. Second, dimples that were not deformed by oxidation collected hard oxide wear particles inside, which reduced the occurrence of abrasive wear.