Effect of mechanical properties of substrate and coating on wear performance of TiN- or DLC-coated 316LVM stainless steel

In order to improve the tribological properties of 316LVM medical grade stainless steel, TiN and DLC coatings were deposited. The TiN coating was prepared by CAE-PVD (Cathodic Arc Evaporation), whereas DLC was deposited by the PACVD (Plasma-Assisted Chemical Vapor Deposition) technique. Surface roughness, nanohardness, and anti-wear performance for both coated and unmodified specimens, as well as adhesion of the coatings were evaluated. The results show that the H-COATING/E-COATING and E-COATING/E-SUBSTRATE ratios significantly affect the anti-wear and scratch performance of the thin coatings. As a result, remarkably different wear and cracking patterns are observed for the two thin films. In wear tests, the prevalent wear mechanisms of TiN coating are tribochemical wear, oxidation of wear debris and counter material transfer. However, the DLC coating undergoes wear by ploughing induced by small patches of the film detached from the substrate. What is more, in scratch tests, for the DLC coating a deformation regime of six stages was found to operate on the basis of OM and SEM observations, whereas for TiN coating four main cracking stages were registered. Nevertheless, despite its unsatisfactory performance in wear tests, in scratch tests, TiN provides better adhesion to the substrate than DLC.