Understanding the wear behaviour of non-doped and Si,O-doped diamond-like carbon films

Abstract

Two diamond-like carbon coatings have been examined, both prior to, and post tribotesting. Physical-chemical characterisation allows the elucidation of both the physical and tribochemical mechanisms underpinning the respective wear behaviours. The wear of the undoped a-C:H DLC coating is far lower than that of the Si,O-doped DLC. Both coatings show formation of protective tribofilms with tribochemically-relevant elements derived from the lubricant additives; however the tribofilms on the two coatings exhibit key differences, with one containing pyrophosphate. The undoped a-C:H DLC coating shows an increase in non-planar sp2 carbon content during wear testing which appears to be at the expense of sp3-hybridised carbon. In comparison, the Si,O-doped DLC undergoes comparatively little change in carbon hybridisation state.