Lubrication mechanisms of graphene for DLC films scratched by a diamond tip

The lubrication behavior of graphene for diamond-like carbon (DLC) films scratched by a diamond tip is investigated by molecular dynamics (MD) simulations. Graphene can efficiently lubricate the DLC film, and its lubrication performance can be improved by the increase of its layer number but be degraded by its defects and large size. The friction mechanisms of graphene during its lubrication highly depend on normal force, F _N. Under a small F _N, a superlow friction force, F _f, is obtained which represents the super-lubrication of graphene. Under a large F _N, the F _f increases due to the tribochemical reactions of graphene. Such reactions happen before the rupture of the graphene, which indicates the limitations of the super-lubrication of graphene in realistic situations.