Toward ultralow friction and wear of ultrananocrystalline diamond film by formation of graphene nanosheets with a Cu catalyst

The present work has realized ultralow friction and wear of ultrananocrystalline diamond (UNCD) film through in-situ formation of graphene nanosheets by introducing Cu catalyst. UNCD film was first coated with a Cu layer by magnetron sputtering method and then annealed with the protection of Ar. After that, some thin and wrinkled graphene-like nanosheets were in-suit formed in UNCD film, which avoided the contamination of graphene during transfer process and enabled better adhesion between graphene and UNCD film. A comparative study of tribological behavior of UNCD, Cu/UNCD and annealed Cu/UNCD films were performed against Si3N4 ball on a ball-on-disk tribometer. The results showed that graphene nanosheets over UNCD film enhanced its tribological performance evidently. The annealed Cu/UNCD film exhibited ultralow friction coefficient of 0.025 and a kind of zero wear as the wear track is higher than the film surface. The findings in this study present a novel and effective method to enhance the lubricity of any engineering UNCD film.