Mechanism of tribofilm formation on Ti6Al4V oxygen diffusion layer in a simulated body fluid.

An Oxygen Diffusion Layer (ODL) was generated on the surface of Ti6Al4V alloy by thermal oxidation treatment. In vitro tests for cytotoxicity were performed in the presence of Ti6Al4V and the ODL samples with the culture of G292 Cells using MTT assay. The results showed a similar cell viability in the presence of the both samples. Wear behaviour of Ti6Al4V and the ODL samples was investigated in a phosphate buffered saline solution under a normal load of 30N at a sliding velocity of 0.1m/s. The worn surface and subsurface of the samples were studied using SEM, STEM, TEM, XPS, AFM, nano-hardness and surface profilometry. A bio-tribofilm was observed on the worn surface of the ODL. TEM studies showed that the tribofilm had an amorphous structure and contained oxygen and phosphorous as confirmed by XPS and EDS analysis. AFM images also revealed that the tribofilm consisted of compacted fine debris. The formation of the tribofilm on the ODL with higher hardness and strength resulted in a decrease of about 95% in the wear rate compared with Ti6Al4V alloy.