Behaviour of MoDTC in DLC/DLC and DLC/steel contacts

Diamond-like carbon (DLC) coatings are beginning to be used on machine components parts because of their excellent friction and wear resistance properties. It is hence important to be able to formulate lubricants able to work effectively with these coatings. This requires knowledge of how the various surface-reactive additives generally employed in lubricants behave with DLCs. This paper compares the behaviour of seven types of DLC, a-C, a-C:H, a-C:H:W, a-C:H:WC, Si-DLC, ta-C, ta-C:H, lubricated with molybdenum dialkyldithiocarbamate (MoDTC) solution. It is found that a-C and a-C:H:WC give lower boundary friction than the other types of DLC. MoDTC improves the wear resistance of DLC/DLC contacts but appears to greatly degrade the wear resistance properties of some DLCs in DLC/steel contacts, even though Mo-derived tribofilms form on all DLCs.