Friction behaviour and mechanism of a-C films in hydrogen, nitrogen, and oxygen atmospheres: Insights from reactive molecular dynamics

Abstract

In this work, the friction mechanism of amorphous carbon (a-C) films in hydrogen (H2), nitrogen (N2), and oxygen (O2) atmospheres are investigated by using reactive molecular dynamics simulations. It is found that the a-C film has the highest friction in the H2 atmosphere and ultra-low friction in the O2 atmosphere. Further studies show that a-C films are difficult to passivated by H atoms. The violent diffusion of H atoms to a-C film under the action of high friction temperature leads to the increase of C atom density at the friction interface, resulting in high friction. In the O2 atmosphere, O atoms almost do not diffuse to the a-C film, mainly exist at the friction interface, weaken the density of C atoms, and form gas-dynamic lubrication to produce ultra-low friction. In addition, graphitization and passivation are not the key factors determining the low friction in the gas atmosphere.