Environment-dependent tribochemical reaction and wear mechanisms of Diamond-like carbon: A reactive molecular dynamics study

Diamond-like carbon (DLC) is widely utilized in various fields as a promising solid lubricating material. However, the lubricity and wear behaviors of DLC are highly sensitive to the environment, and the relevant mechanisms are hidden by complex tribochemical reactions at the friction interface. In this study, we performed reactive molecular dynamics (RMD) simulations of DLC to clarify the wear mechanisms in various environments (vacuum, water, and oxygen environments). Two types of tribochemical reaction-induced wear were observed: chemical wear induced by the triboemission of C_xH_y and C_xH_yO_z compounds and mechanical wear induced by the formation of interfacial C–C bonds. Moreover, the results revealed that the environment affects the tribological behavior of DLC primarily through its impact on the surface chemical state, that is, the quantity and type of surface terminations. In terms of the number of surface terminations, the more surface terminations there are, the more chemical wear and less mechanical wear they cause. In particular, oxygen-containing terminations (e.g., C–OH and C=O) are more resistant than H terminations to interfacial bond formation and mechanical wear. The present work provides important insights into the wear mechanisms of DLC, aiding in the reduction of DLC wear by controlling the environment.