Perspectives of the Friction Mechanism of Hydrogenated Diamond-Like Carbon Film in Air by Varying Sliding Velocity

The purpose of the present work is to probe the friction mechanism of hydrogenated diamond-like carbon (H-DLC) film in air by varying sliding velocity (25-1000 mm/s). Friction tests of Al2O3 ball against H-DLC film were conducted with a rotational ball-on-disk tribometer. As the sliding velocity increases, both the friction coefficient and the surface wear of H-DLC film decrease, reach the minimum values, and then increase in the high sliding velocity region. Based on the observed results, three main friction mechanisms of H-DLC filmnamely graphitization mechanism, transfer layer mechanism, and passivation mechanismare discussed. Raman analysis indicates that the graphitization of worn surface on the H-DLC film has a negligible contribution to the variation of the friction coefficient and the surface wear. The origin of the sliding velocity dependence is due to the synergistic interaction between the graphitized transfer layer formation and the surface passivation. The present study will not only enrich the understanding of friction mechanism of H-DLC films in air, but will also help to promote their practical engineering applications.