Tribological behaviour and microscopic wear mechanisms of UHMWPE sliding against thermal oxidation-treated Ti6Al4V

Tribological behaviour of ultra-high molecular weight polyethylene (UHMWPE) pins sliding against thermal oxidation (TO)-treated Ti6Al4V alloy discs with different levels of average surface roughness was investigated under water lubrication conditions. When rubbing against a smooth counterface (Ra<0.030–0.035 μm), UHMWPE was found to be worn predominantly via a micro-fatigue mechanism. To advance the scientific understanding of the microscopic wear mechanisms of UHMWPE, a technique involving permanganic etching coupled with high resolution SEM analyses of wear surfaces and cross-sections was adopted to yield new insight into the micro-fatigue mechanism. It was found that stress-induced preferential orientation of the crystalline lamellae in the UHMWPE led to the origin of ripples containing micro-cracks at their valleys. The cyclic loading promoted lateral propagation and inter-connection of these micro-cracks, thus giving rise to eventual spallation of the surface material as wear debris. Based on the experimental results, a micro-fatigue wear mode is proposed.