Theoretical approach for the quantification of wear mechanisms on the nanoscale

The occurrence of wear between two unlubricated surfaces in relative motion one against the other presents several open questions, both on the macroscale and nanoscale. This paper takes as a starting point some experiments of wear tests on ionic crystals that have recently been presented. Two different wear mechanisms are discussed for the interaction of an atomic force microscopy probe tip with a flat atomic surface making use of a 2D system. The effects of shear forces and the Van der Waals force are analysed with a numerical model in order to give the occurrence of abrasive- and/or adhesive-wear mechanisms. The idea underlying the work is that adhesive or abrasive contributions to wear are critically dependent on the potential conformation of surfaces and the Lennard-Jones potential between the probe tip and flat atomic surface. The atoms involved in the wear processes can be subject to adherance to the probe tip if the vertical forces are most prominent with respect to shear forces that, in contrast, would involve atoms in an abrasive mechanism. The numerical results are based on a diffusive model both for adhesive- and abrasive-wear mechanisms. This diffusive model allows wear volume quantification by making use of a simple formula. Due to its simplicity, the model adopted could be helpful to understand the occurrence of different wear mechanisms on the nanoscale.