Theoretical superlubricity and its friction stability of amorphous carbon film induced by simple surface graphitization

Abstract

Amorphous carbon (a-C) film as one of the most promising superlubricious materials arouses much attention from technical and industrial fields. However, the superlubricious state of a-C film strongly depends on the formation of special nanostructures or components, increasing the difficulty and complexity of the preparation process. Reducing the friction coefficient of a-C film to superlubricity is still a challenge for industrial scale-up. Herein, a simple and effective approach is proposed to achieve superlubricity by in-situ formation of graphitized structure at a-C surface via fast annealing. Results reveal that the friction property closely depends on the graphitized degree of mated a-C surfaces and the friction coefficient below 0.01 or even 0.001 can be obtained for the highly graphitized system. In particular, under extreme working condition, it also demonstrates excellent stability and reliability of superlubricious behavior. This is not only mainly attributed to the decrease of spacing distance between mated graphitized structures following the high repulsive force, but also related to the tight anchoring of graphitized structure to the intrinsic a-C. In addition, compared to the widely applied surface passivation approach, the graphitization modification of a-C surface exhibits higher effectiveness in super -lubricity without deteriorating the intrinsic mechanical properties of a-C film.