A tribochemical evaluation of a WC–DLC coating in EP lubrication conditions

Improvement of fuel economy and component durability as well as reduction of dependence on some harmful components of lubricants are the key concerns for automotive industries. In recent years, efforts have been made to use surface engineered surfaces in automotive components to produce environmentally friendly vehicles as well as to increase fuel economy. Since commercially available lubricants are mainly optimised for effective lubrication of ferrous materials, effective lubrication of novel materials, especially in the boundary lubrication/EP regime, is not well understood. Published research has also indicated that lubricant chemistry could have a detrimental impact on the intrinsic coating properties, changing their mechanical properties. Tribological systems working in boundary lubrication/EP conditions rely on lubricant–additive interactions to initiate surface reactions. The performance (friction-related efficiency and wear-dependent reliability) of tribological systems depends on the time taken to initiate surface reactions, the nature of the surface reactions and the stability of the films formed as a result of the surface reactions. This paper is a fundamental study of the lubrication and wear mechanisms of a WC-doped diamond-like-carbon (DLC) coating when lubricated in the extreme pressure (EP) regime.