Wear mechanism of Mo-W doped carbon-based coating during boundary lubricated sliding

The high temperature tribological applications of state-of-the-art diamond-like-carbon (DLC) coatings in automotive industry are often compromised due to their poor adhesion strength and low thermal stability. A molybdenum and tungsten doped carbon-based coating (Mo-W -C) is developed in order to overcome these limitations and to enhance tribological performance during boundary lubricated sliding at ambient and elevated temperature. The coating was deposited utilis-ing HIPIMS technology. MoW -C coating showed lowest mean friction coefficient (µ = 0.033) compared to a number of commercially available state-of-the-art DLC coatings when pin-on-disc experiments were carried out at ambient temperature. Similarly at 200°C, a significant reduction in friction coefficient was observed for MoW -C coating with increase in sliding distance unlike DLC coating. Raman spec-troscopy revealed importance of combined Mo and W doping and tribochemically reactive wear mechanism of MoW -C coating during sliding. The significant decrease in friction and wear rate was attributed to the presence of graphitic carbon particles (from coating) and 'in-situ' formed metal sulphides (WS 2 and MoS 2 , where metals from coating and sulphur from oil) in transfer layer.