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

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.