Covalent graphene-diamond heterostructure coating on tool surface with enhanced lubricity and anti-wear performance

Graphene possesses extraordinary mechanical strength while it is difficult to integrate graphene layers on macroscale mechanical components due to the weak adhesion strength. In this work, we integrated a top layer of graphene sheets on the diamond-coated tool through in-situ growth of graphene on the diamond grains. With the aid of liquid metal catalyst, ultrastrong C-C covalent bonds are formed in the graphene-diamond interface, which can radically eliminate the peeling off of graphene sheets due to the insufficient adhesion strength. Cutting tests revealed that this top-layer graphene can substantially reduce cutting force and tool flank wear when cutting high-silicon aluminum alloy, with the reduction respectively reaching 40 % and 20 %. During the machining process, the graphene sheets are flattened and they gradually form a compact layer covering on the diamond surface, which can not only lubricate the tool surface but also protect the diamond from wear with the ultrahigh intrinsic strength. Further cutting experiments demonstrated that the effectiveness of the graphene sheets can sustain over 3600 m of cutting distance. The achievement in this work provides a novel insight into the integration of covalent graphene-diamond heterostructures in mechanical systems/devices with outstanding macroscale lubricity and anti-wear performance.