Friction and wear performance of diamond-like carbon and Cr-doped diamond-like carbon coatings in contact with steel surfaces

The development of modern engines involves the use of new materials such as diamond-like carbon (DLC) coatings. As these coatings possess different mechanical and physical characteristics to steel, investigation of their friction and wear properties when rubbing against a steel counterpart in a lubricated environment is needed. Specific tests were used to assess the tribological behaviour of these new surfaces (specifically an undoped DLC and a chromium-doped DLC coating). Chemical analyses were also performed in order to evaluate the reactivity of the formulated oil on the various surfaces. The results of the present work clearly show that there was no evidence of tribochemical reaction on DLC coatings. Anti-wear additives were still reacting on the steel counterpart for the undoped DLC case, resulting in better wear properties for the coating. The addition of a metal to the amorphous carbon matrix led to an improvement in wear but inhibited/removed the anti-wear film on the steel counterpart.