Fundamentals of the Tribology of DLC Coatings

This chapter provides an overview of the fundamental processes that may govern friction and wear of diamond-like carbon (DLC) coatings. First, the general cases of traditional and carbon-based solid lubricants in tribology are considered, since they exhibit low friction and high wear resistance. The emphasis is then shifted to DLC films and the specific contributions of three main phenomena — abrasion, adhesion, and interfacial shearing — are considered in detail in order to account for the very interesting tribological behavior of these films. Corresponding critical parameters are identified and their roles are evaluated with respect to the known structures and properties of most DLC films. Finally, the specific examples of adhesive phenomena controlling friction and wear during tests in ultrahigh vacuum (UHV) are discussed. Adhesion appears to be necessary for tribofilm buildup and hence friction reduction; however, continued occurrence of strong adhesive phenomena is detrimental to the superlow friction behavior of these films. Overall, the exceptional tribological behavior of DLC films appears to be due to a unique combination of surface chemical, physical, and mechanical interactions at their sliding interfaces.