Influence of cross-shear and contact stress on the wear of UHMWPE on boost-diffusion-treated additively manufactured Ti-6Al-4V

The more widespread adoption of additive manufacturing (AM) in the biomedical industry has enabled the production of patient-specific implants. When used in joint replacements (or as a bearing material), it is essential to understand the wear behaviour of additively manufactured implants when subjected to loading and motion that simulate their intended use. The aim of this study was to investigate the influence of cross-shear and contact stress on the wear behaviour of ultra-high molecular weight polyethene (UHMWPE) against boost-diffusion-treated (BD-treated) AM Ti-6Al-4V under varying conditions. Multidirectional pin-on-plate wear testing was conducted across cross-shear ratios from 0 to 0.3 and contact stresses ranging from 0.56 to 14 MPa. Surface characterisation techniques were used before and after wear testing to gain insights into the wear mechanisms. The wear of UHMWPE against BD-treated Ti-6Al-4V was compared to that of CoCr and untreated wrought Ti-6Al-4V. Results revealed that against BD-treated Ti-6Al-4V, UHMWPE wear was initially high due to the high surface roughness; however, continued wear testing led to polishing of the BD-treated Ti-6Al-4V, a reduction in the dynamic friction coefficient, and a decrease in wear rate. The high initial surface finish of the BD-treated Ti-6Al-4V resulted from the oxidation heat treatments. However, following wear testing surface degradation was absent, highlighting the potential benefit of the surface treatment in AM patient-specific implants.