Effect of environmental hydrogen atoms on the tribological behaviors of diamond-like carbon films

•Environmental H atoms can significantly reduce the friction of DLC films.•At low friction temperatures, the friction is reduced by C atom passivation.•At high friction temperatures, friction reduction is induced by H atoms diffusion.

Influence of environmental H atoms on the tribological behaviors of DLC films is investigated via molecular dynamics simulations. These H atoms significantly reduce the friction force, and the reduction mechanisms depend on friction temperatures. At low friction temperatures, the H atoms are concentrated near contact interfaces, and their passivations highly reduce the interfacial adhesion, resulting in the low friction force. However, high friction temperatures induce the significant diffusion of the H atoms into the DLC films and thermally expand such films and increase their graphitization, causing a wide region with easy-shear properties to reduce the friction force. It is believed that these mechanisms of friction reduction can improve the understanding of the superlow friction of DLC films in H2 environment.