Synergistic effect of physical and chemical reactions on friction behaviors of DLC films in humid air

Effect of tribochemistry on the friction behavior of diamond-like carbon (DLC) films in humid air has been investigated via ReaxFF simulation. The tribochemical reactions can induce the generation of functional groups and thus cause a passivated contact interface to reduce friction. Moreover, the tribochemical reactions can generate many gas molecules which can prevent the formation of interfacial C-C covalent bonds and thus reduce interfacial adhesions. The lamellar structure which is due to the common effect of high temperature and the pull of the carbon chains can reduce friction. It is found that the lamellar structure formed from physical reactions allows a large diffusion space for water and oxygen molecules to rapidly react with certain sites, and the functional groups formed from the chemical reactions can stabilize the lamellar structures under external loading and lateral sliding. Therefore, the physical and chemical reactions of DLC films show a synergistic effect on their friction behaviors in humid air.