Tribocorrosion response of PVD molybdenum nitride (MoN) coated Ti-6Al-4V

Ti-6Al-4V is a widely used biomedical alloy, valued for its biocompatibility, high corrosion resistance and mechanical strength. However, its poor tribological performance limits its use in frictional contacts. This limitation can be addressed by enhancing surface properties through coatings that impart enhanced degradation resistance. Molybdenum nitride (MoN) based coatings are promising candidates for bio-tribological use due to their ability to attain high hardness (∼37 GPa), stemming from strong primary bonding. Moreover, even if small amounts of molybdenum ions are released, they are unlikely to elicit adverse biological effects due to the ability of the body to regulate molybdenum level through homeostatic processes. This study investigates the tribocorrosion performance of two MoN PVD coatings, deposited on Ti-6Al-4V substrates at different nitrogen partial pressures via unbalanced reactive magnetron sputtering. Electrochemical behaviour and tribocorrosion response were evaluated in Ringer's solution under elastic contact conditions. A reciprocating sliding configuration against an alumina ball counterface was used and tribocorrosion tests were conducted under both open circuit potential and anodic potential conditions. The MoN coated Ti-6Al-4V variants exhibited a markedly reduced tribocorrosion material loss compared to the untreated alloy under both electrochemical conditions. The coatings exhibited resistance to blister formation and caused minimal damage to the counterface alumina ball during tribocorrosion testing.