Exploring the role of surface hydrogenation in anti-friction of circular-textured amorphous carbon film from the atomic level and its dependence on textured shape

Abstract

Hydrogenating the amorphous carbon (a-C) surface can achieve the ultra-low friction performance. However, the effect of surface hydrogenation on anti-friction of textured a-C surface, especially its dependence on different textured shapes, is still lack of study; the information on the complicated friction interfacial also remains unclear due to the limitation of in-situ characterization in experiment. Here, the friction behavior of circular-textured a-C film was investigated by reactive molecular dynamics simulations, and its dependence on the hydrogenated degree of textured a-C surface was mainly focused, in which the effect from textured shape was also comparatively studied. Results show that the anti-friction efficiency of the circular-textured a-C film strongly depends on the surface hydrogen content; when the surface H content is 31.0 %, the friction coefficient decreases by 97.5 %, which is attributed to the passivation effect of H atoms on the a-C surface, inhibiting the generation and crosslinking of unstable dangling bonds. Moreover, the migration of H atoms in the friction process provides a strong repulsive force, which also significantly reduces the shearing strength of the interface and the friction coefficient. In particular, further study discloses that the effect of textured shapes of a-C surface on friction behavior is also related with the surface H content; with the increase of H content, the textured shape of a-C surface, which exhibits the low-friction performance, transforms from rectangular to circular-textured one, and the corresponding low-friction mechanism also changes from the passivation of friction interface to H-induced repulsive effect. These results provide an effective way to develop an efficient a-C anti-friction system.