Selective Wear Behaviors of a Water-Lubricating SiC Surface under Rotating-Contact Conditions Revealed by Large-Scale Reactive Molecular Dynamics Simulations

Atomic-scale wear mechanisms and tribochemical reaction dynamics on the surfaces of rolling contact parts are rarely studied by computer simulations owing to the prohibitive computational cost. Here, using water-lubricated silicon carbide (SiC) as an example, we study the atomic-scale friction/wear mechanisms and tribochemical reactions in the rolling contact state for the first time by applying our large-scale reactive molecular dynamics simulator in conjunction with the supercomputing system MASAMUNE-IMR. The rolling friction simulation results interestingly revealed that in both vacuum and water environments, the wear of silicon atoms always occurred prior to that of carbon atoms from the SiC surface. In vacuum, the wear of SiC occurred predominantly through interfacial adhesion and subsequent adhesion-induced atom transfer from the original surface to the countersurface. In contrast, in the water lubrication, the rotation of the hydrophilic SiC surfaces brought the surrounding water molecules into the contact interface to form a third-body water layer that prevented interfacial adhesion, and hence greatly reduced the adhesive wear of SiC; however, wear through the triboemission of surface SixHyOz groups slightly increased owing to the reactions of SiC with water, representing a minor drawback of the water lubrication. The above results indicate an interesting selective wear of silicon atoms from the SiC surface during the rolling friction state, which differs from the sliding friction case in which the numbers of worn-out carbon and silicon atoms were almost identical. This work provides a new perspective for elucidating the atomic-scale mechanisms at rolling contact interfaces.