Tribochemistry of silicon and oxygen doped, hydrogenated Diamond-like Carbon in fully-formulated oil against low additive oil

Diamond-like Carbon (DLC) coatings are increasingly used to reduce wear and lower friction in many applications. Doped DLCs are being produced with the goal of further enhancing the friction and wear profile as well as increasing the coating reliability. Silicon is often incorporated into DLC as it is known to affect the sp2/sp3 ratio which in turn can affect the hardness of the film. It can also improve adhesion of the DLC coating to the substrate and lower internal stress. In this study, investigations into the wear behaviour, tribochemistry and oil-formulation dependence of Si, O-doped DLC (Si-DLC) were conducted. The oxidative stability of Si-DLC was also examined. Silicon-doped DLC is able to form a protective tribofilm when a fully-formulated lubricant is used. The tribofilm is composed of S, P, Ca and Zn which are widely recognised as being important to wear reduction. A mechanism of wear repression facilitated by oil additives is proposed.