Tribological behavior of in situ fabricated graphene-nickel matrix composites

Graphene-nickel (G-Ni) composites were in situ fabricated by a powder metallurgy method. The effects of graphene content on the tribological behavior of G-Ni composites were investigated. The tribochemistry and structural evolution of graphene were analyzed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy to understand the lubricating role of graphene in the G-Ni composite. The results show that graphene protects the nickel matrix from severe oxidation at the expense of its oxidation during sliding friction. Graphene on the friction interface transforms from a structure with less defects to a disordered amorphous structure. Polymeric segments are also generated by the tribochemical reactions of graphene. The formation of the tribofilms containing amorphous carbon and polymers is responsible for the self-lubricating behavior of the G-Ni composites.