Comparison of dry sliding friction and wear of Ti6Al4V alloy treated by plasma electrolytic oxidation and PVD coating

Titanium alloys, due to their excellent combination of low density, high strength to weight ratio, high corrosion resistance and biocompatibility, are widely used in the aerospace, automotive, chemical and biomedical industries. However, a main limit to the use of Ti alloys is their poor tribological behaviour. For this reason, different surface treatments and coatings have been developed for improving surface properties of Ti alloys. Among the most recent surface modification techniques, plasma electrolytic oxidation (PEO) has been successfully applied to titanium alloys. The aim of the present study was to investigate the friction and wear behaviour of a PEO coating on the Ti6Al4V alloy. The tribological behaviour of the PEO treated Ti alloy was compared with that of thin PVD coatings, such as TiN, (Ti,Al)N and CrN/NbN superlattice deposited on the same substrate. The tests were carried out under dry sliding conditions (slider-on-cylinder geometry) against a plasma-spray Al2O3–TiO2 coated steel. TiN gave the best tribological performance among the PVD coatings, up to 20 N. The PEO treatment significantly reduced both wear and friction of the Ti6Al4V alloy, even under higher applied loads, up to 35 N.