The effect of humidity on the tribological behavior of diamond-like carbon (DLC) film coated on WC-Co by physical vapor deposition method

DLC films have been coated by PVD on WC-Co substrate with and without Si interface. They have been tested under low (∼20%) and high (∼80%) humidity conditions by reciprocating friction and wear apparatus. For ascertaining the wear mechanism from the topographies of DLC films, optical and SEM images of wear tracks have been taken. Wear debris particles behave as an abrasive agent, depositing into the film and causing the start of failure. There are multiple wear mechanisms, such as fatigue, abrasion, etc., existing simultaneously in the wear of DLC film in both cases. Wear rate decreases as the total wear way increases. For the case of DLC coating without Si interface there is a good correlation between wear rate and friction coefficient. However, this harmony disappears for DLC/Si coating. A chemically activated process may be assumed as the controlling step in the micro crack propagation during the generation of a wear debris particle. The different tribological behaviors of the DLC coatings under different environmental conditions are explained.