Environment-Dependent Wear Mechanisms of Diamond-Like Carbon/Fe Interface under H2O and HNO3 Aqueous Environments: A Reactive Molecular Dynamics Study.

Corrosive wear at metal interfaces under aggressive environments poses a major challenge to the durability of engineering components. In internal combustion engines, exhaust gas recirculation promotes the formation of nitric acid (HNO3), accelerating the surface degradation of steel. In this study, reactive molecular dynamics simulations were employed to elucidate atomic-scale wear mechanisms at the diamond-like carbon (DLC)/iron (Fe) friction interface under H2O and HNO3 aqueous environments. In the presence of H2O, adhesive wear predominates because the Fe substrate fails to develop a protective oxide layer within the simulation time scale. Consequently, Fe atoms form Fe-C bonds with the DLC surface and are removed during sliding. In contrast, when both H2O and HNO3 are present, corrosive wear dominates while adhesive wear is suppressed. HNO3 reacts with the Fe surface to produce a layered Fe oxide and Fe nitride, which limit direct Fe-C bonding. During sliding, H2O reacts with Fe-N bonds within the nitride layer, forming Fe-NH2 structures. These reactions result in the detachment of the nitride layer as tribochemical debris whereas the oxide layer remains stable. Overall, the dominant wear mechanism at the DLC/Fe interface is environment-dependent: adhesive wear prevails in H2O, while corrosive wear becomes significant in the HNO3-H2O environment.