Enhancing fretting performance of 316L biomedical alloys through duplex TiN and DLC coatings

This study investigates the use of duplex coatings, TiN/diamond-like-carbon (DLC), on improving the tribological performance of stainless steel 316L which is commonly used for femoral stems in total hip replacement implants. A range of substrate pre-treatment variants (nitriding and polishing) were applied to investigate the impact on the mechanical and tribological performance of the coatings. The tribological performance of plasma vapour deposition duplex coating variants was tested using a bespoke in-house fretting tribometer with an electrodynamic shaker utilising a ball-on-plate configuration. Fretting was replicated by applying micro-motion to the Ø12 Al₂O₃ ball relative to duplex coated SS 316L plates under a dead weight normal load. Un-polished substrates prior to the coating deposition led to improved tribological performance likely due to improve coating adhesion to the substrate surface. The hydrogenated DLC sample variants showed lower friction performance compared to hydrogen-free DLC variants most likely due to higher amounts of graphitisation.