Influence of hydrogen and tungsten concentration on the tribological properties of DLC/DLC contacts with ZDDP

Diamond-like carbon (DLC) coatings are becoming potential candidates for automotive engine parts because of their excellent friction and wear resistance properties. It is important to understand their film-forming, friction reduction and wear resistance mechanisms. This paper studies the influence of hydrogen and tungsten concentration in DLCs on friction and wear by comparing the behaviour of one a-C, five a-C:H and four a-C:H:W coatings in DLC/DLC contacts lubricated with base oil and a ZDDP solution. a-C show lower boundary friction than the other types. W-DLCs experience higher wear compared to the other coatings. Over the range of concentrations studied, hydrogen and tungsten contents do not affect friction greatly but have a marked effect on adhesion, film-forming and wear properties.