Doping effects on the tribological performance of diamond-like carbon coatings: A review

Diamond-like carbon (DLC) coatings have garnered considerable interest due to their unique features, which include wear resistance with a low friction coefficient, high hardness, biocompatibility, and chemical inertness. Their tribological performance is highly dependent on tribological environment, structure, and mechanical properties of the coating. A major problem that can adversely impact the tribological properties of the DLC coating is insufficient adhesion to the substrate. This issue caused by mismatch of the substrate and coating thermal expansion coefficient (TEC) and high amount of internal stress in DLC coating. The limitations of DLC coatings for tribological performance can be overcome by incorporating different types of metallic and non-metallic elements into the coating structure. Recently, various efforts have been made to address this issue by doping certain elements into the DLC coating, including fluorine, nitrogen, silicon, and metals. This review discusses new advancements in doped DLC coatings designed to improve their tribological behavior in different specific applications such as high relative humidity, elevated temperature, and bio-implant.