Origin of low friction for amorphous carbon films with different hydrogen content in nitrogen atmosphere

To date, hydrogenated amorphous carbon(a-C:H) film is a promising solid lubricant to meet growing needs for energy-saving and environmentally friendly. Here, friction behaviors of four a-C:H films with different hydrogen content in high purity N-2 atmosphere are compared and they all behave low friction and wear rates. Detailed experimental studies reveal that N-2 atmosphere-induced graphited transfer films and hydrogen passivation have synergic effects on low friction for different a-C:H films. Besides, N-2 molecule adsorbed on the sliding interfaces due to pi-pi*, -C-H center dot center dot center dot pi and O center dot center dot center dot pi interactions also accounts for low friction in N-2 atmosphere. This work will provide a new pathway for reducing friction and wear by applying gas lubrication to engineering fields.