Friction-induced metastable transformation of amorphous carbon film: Exploration by experimental and molecular dynamics simulations

The previous experimental research showed that the structure of the amorphous carbon film transformed from sp3-C atom to sp2-C atom after the frictional process. However, due to its metastable characteristics of the amorphous carbon film, whether the transformation can occur from the sp2-C atom to the sp3-C atom during friction is unclear. This study is conducted to get an insight into the effect of frictional load and velocity on the structural transformation of the amorphous carbon film. The relevant results have shown that due to the effect of pressure and shear force, the amorphous carbon film generates sp3-C atoms during the friction process, and this metastable structural transformation recovers with the disappearance of the force. Furthermore, there are differences in the effects of frictional load and velocity on structural transformation. The increased frictional load and velocity inhibit the increase in the proportion of sp2-C atoms, and the structural order of the frictional contact interface is significantly enhanced under a larger frictional load, while the frictional velocity has no obvious effect in this regard. The proportion of sp2-C atoms and the degree of structural order of the friction contact interface in combination affect the tribological performance of the amorphous carbon film.