On the uniqueness of wear coefficient for abrasive wear at nanoscale

Materials wear is often characterized by empirical relations as the physical and chemical interactions at sliding interfaces are not fully understood at any length scale. Recent studies showed that these wear relations do not always hold in particular at the nanoscale. Here we discuss the validity range and limitations of two well-known wear models, i.e. Archard's and Reye's ones (which were principally developed for adhesive wear) for abrasive wear process. Using systematic long-timescale molecular dynamic nanoscratching simulations, we show that, at the nanoscale, the wear coefficient increases by the adhesion strength and scratching depth and eventually saturates to a constant value. The saturation is associated with the transition from atomic attrition wear mode to plasticity-induced wear. This new understanding rationalizes discrepant experimental observations on the validity of Archard's wear relation at the nanoscale. Furthermore, it confirms that a depth- and adhesion-independent wear coefficient can be obtained when plastic deformation dictates the abrasive wear process.