Structural and environmental dependence of superlubricious properties in hydrogenated Graphite-Like carbon Films: Implications in solid state lubrication

A variety of sp2-bonded structures can be formed in carbon materials, and carbon-based lubricants with low shear strength are widely used for harsh working conditions. In this paper, hydrogenated graphite-like carbon (GLC) films with a high content of sp2-bonded structures were prepared by ion beam deposition. Their structures were modified by heat treatment (annealing) and element doping to improve the lubrication performance. The microstructure characterization of tribolayer formed at friction interfaces and the lubricating mechanism were analyzed thoroughly, and an appropriate modification method of sp2-bonded structures was then proposed. Controlling the sp3 cross-linked structures between sp2-bonded carbon could improve the lubrication performance precisely. The results regarding GLC films against tribopairs with different hydrogen contents indicate that a stable friction coefficient (0.006) can be obtained in dry N2 when GLC film and hydrogenated polymer-like carbon (PLC) coated ball were used as tribocouples, and the wear rate is only 6.71×10-10 mm3/N·m after 100,000 reciprocating cycles. By utilizing the high sp2-bonded carbon films, a theoretical basis for superlubricity can be established through heat treatment and element doping, which provides the sufficient technical support for the development of solid lubricating materials with low friction coefficients and high wear resistance under harsh working conditions.