Wear Mechanism of Mo-W Doped Carbon-Based Coating during Boundary Lubricated Sliding

Abstract

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 utilising HIPIMS technology.Mo-W-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 Mo-W-C coating with increase in sliding distance unlike DLC coating.Raman spectroscopy revealed importance of combined Mo and W doping and tribochemically reactive wear mechanism of Mo-W-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.