Tribological reactions between oil additives and DLC coatings for automotive applications

In the past, the development of modern engines and transmissions would have been impossible without advanced lubricant additive chemistry and proper lubricant formulation. Introduction of diamond and diamond-like carbon (DLC) coatings, especially metal doped DLC coatings, opens further possibilities in improving performance of engine and transmission components, which cannot longer be achieved only by lubricant design. However, the lack of knowledge on tribological behaviour of DLC coatings when lubricated with oils originally designed for metallic surfaces limit their use in practical applications. The results of the present investigation clearly show the existence of tribochemical reaction between metal doped DLC coatings (W-DLC) and S-based EP additives, while for a-C:H coatings additives had no influence. Furthermore, tribological behaviour of W-DLC coatings was found to be EP additive concentration and contact temperature dependant.