Friction behaviors of DLC films in an oxygen environment: An atomistic understanding from ReaxFF simulations

This work investigates the influence of oxygen on the friction behaviors of diamond-like carbon (DLC) films via ReaxFF simulation. It is found that friction reductions are dominated by physical absorptions of oxygen on DLC surfaces in the initial sliding stage, but are determined by chemical absorptions of oxygen after friction stabilizations. More oxygen molecules can further reduce friction by inducing more C-O groups which are hard to destroy under external loading and sliding. Furthermore, the generations/dissociations of CO and CO2 molecules are observed in sliding interfaces and depend on temperatures and mechanical mixing. It is found that the presence of C-O groups and CO and CO2 molecules may help to induce the formation of lamellar structures at sliding interfaces. •Friction reduction of DLC films is due to physical/chemical absorptions of oxygen.•Generations/dissociations of CO and CO2 molecules happen in sliding interfaces.•Presences of C-O groups and CO and CO2 molecules stabilize lamellar structures.•C-O groups are hard to destroy under external loading and lateral sliding.