Atomic-scale insights into the tribochemical wear of diamond on quartz surfaces

A detailed understanding of diamond wear is crucial due to its use in high-performance cutting tools. Despite being a much harder material, diamond shows appreciable wear when cutting silicon dioxides due to a tribochemical mechanism. Here, we use nonequilibrium molecular dynamics simulations with a reactive force field to investigate the wear of single-crystal diamond tips sliding on α-quartz surfaces. Atom-by-atom attrition of carbon atoms is initiated by the formation of C-O interfacial bonds, followed by C-C cleavage, and either diffusion into the substrate or further oxidation to form CO2 molecules. Water molecules dissociate to form hydroxyl groups, which passivates the surfaces and reduces interfacial bonding and wear. At low loads, the initial wear rate increases exponentially with temperature and normal stress, consistent with stress-augmented thermally activated wear models. At higher loads, the initial wear rate becomes less sensitive to the normal stress, eventually plateauing towards a constant value. This behaviour can be described using the multibond wear model. After long sliding distances, wear also occurs through cluster detachment via tail fracture. Here, wear becomes approximately proportional to the sliding distance and normal load, consistent with the Archard model. The normalised wear rates from the simulations are within the experimentally-measured range.