Tribo-Mechanical Properties of DLC Coatings Deposited on Nitrided Biomedical Stainless Steel

Abstract

Diamond-like carbon (DLC) coatings are frequently considered for biomedical applications due to their attractive tribo-mechanical properties combined with good biocompatibility. In the present work, DLC coatings have been deposited on 316L stainless steel (SS) substrates. The duplex approach consisted of surface nitriding in a radio frequency (RF) discharge for the reinforcement of SS-DLC bonding prior to DLC deposition (0.5 µm thick). Chemical composition and morphology of the nitrided SS were assessed by XPS and SEM, while depth-sensing indentation, ball-on-flat tribometry, and microscratch testing were used to determine the tribo-mechanical performance of the nitrided SS and of DLC coated SS samples. We found that the formation of a thick (∼1–2 µm), hard (15 GPa) metal nitride layer at the SS surface has a strong influence on enhancing the coating adhesion (critical load of 6.5 N) and wear resistance of DLC (wear factor 3–8 × 10−8 mm3 · N−1 · m−1 compared to 10−5 mm3 · N−1 · m−1 for nitrided SS).