Improving tribocorrosion resistance of a medical grade CoCrMo alloy by the novel HIPIMS nitriding technique

In this work, tribocorrosion performance of the High Power Impulse Magnetron Sputtering (HIPIMS) nitrided (F75) CoCrMo alloys was examined with the help of sliding wear corrosion experiments carried out in Hank's solution. Results indicate that under Open Circuit Potentials (OCP), both nitrided and the untreated specimens exhibited near similar Sliding-Wear-Corrosion coefficient (KSWC) values (6.52 × 10−15 and 3.95 × 10−15 m3N−1m−1 respectively). However, the benefits of HIPIMS nitriding were evident under accelerated corrosion (anodic potentials) and passivating conditions. KSWC values of the nitrided specimens were an order of magnitude lower (6.41× 10−15 m3N−1m−1) than the untreated specimens (3.4 × 10−14 m3N−1m−1), indicating that nitrided surfaces had higher resistance against tribocorrosive mechanisms. This superior performance was attributed to the formation of a nitrided microstructure consisting mainly of expanded austenite (ƔN) without the formation of the detrimental CrN phase, which resulted in high hardness and sustained resistance to corrosion. A rationale for lower synergy between wear and corrosion and its relation to the nitride microstructure has been presented.