Mechanical and tribological properties of Si and W doped diamond like carbon (DLC) under dry reciprocating sliding conditions

The mechanical and tribological properties of three types of diamond like carbon (DLC) coatings, i.e., non-doped, Si-doped, and W-doped DLC, are evaluated. Dry reciprocating sliding wear tests were performed to evaluate the effect of sliding frequency/velocity on friction, adhesion, and wear. The degree of graphitization of non-doped and W-doped DLC increases with sliding velocity, which results in a lower coefficient of friction (COF), and a decrease in wear rate. Si-doped DLC, however, exhibits distinct friction behaviour, with increasing COF and severe fluctuations in friction at higher sliding velocities. In Si-DLC frictional heating drives the formation of an oxide-rich tribofilm and large amounts of Si-rich oxide wear debris that are both adhesive and abrasive. The oxide-rich tribofilm, and lack of surface graphitization, result in the severe fluctuations of Si-DLC friction via stick-slip and surface fracture/wear mechanisms, and significantly increased COF and wear rates at higher sliding velocities.