Potential for adhesive wear in friction couples of UHMWPE running against oxidized zirconium, titanium nitride coatings, and cobalt-chromium alloys.

The classical wear mechanisms abrasion, fatigue, and adhesion are the most frequent causes of surface changes of ultra high molecular weight polyethylene (UHMWPE) in artificial joints. The counterpart material has a strong influence on the wear and friction behavior of artificial joints due to its abrasive properties and adhesive interaction with UHMWPE. The formation of a transfer layer on the counterpart in UHMWPE bearing systems is often described as being a clear indication of strong adhesive forces. The influence of using a cobalt-chromium-molybdenum (CoCrMo) alloy, a titanium nitride plasma coating or an oxidized zirconium alloy on adhesive wear was studied. The surface free energy and the bonding forces of these counterpart materials to UHMWPE were investigated. Catalytic effects on the degradation behavior of polyethylene, the micro friction behavior, and the build-up and constitution of a transfer layer deposited under loads, and relative velocities that are relevant in knee joints were analyzed.