High-temperature wear mechanism of diamond at the nanoscale: A reactive molecular dynamics study

• The diamond material mechanically fails at a total stress of 157–165 GPa when subject to a multi-direction frictional contact. • The thermal stress induced by the restriction of thermal expansion is the primary contribution to the wear of diamond. • The interfacial chemical bonding is enhanced with significantly larger contact area and higher friction pucker at the critical temperature. • The substantial increase of sp and dangling bonds is the critical indication for the failure and wear of diamond. Diamond is highly wear-resistant at room temperature, while it suffers from rapid wear under the high-temperature tribological conditions. In this paper, we present a reactive molecular dynamics study to unveil the nanoscale wear mechanism of diamond with the evolution of temperatures. We find a critical temperature over which the mechanical failure and wear of diamond will be significantly accelerated. The diamond structure fails when the total stress reaches 157–165 GPa, which is composed of thermal stress and friction-induced stress. The thermal stress due to the restriction of thermal expansion substantially increases with temperature and contributes a major part to the total stress. At the critical temperature, the interfacial chemical bonding and the frictional contact are strongly intensified, with substantially increased contact quality and contact area. On the other hand, the temperature elevated to the critical value induces a drastic increase of sp and dangling bonds in diamond, leading to the internal collapse of the mechanical strength. Ultimately, the synergy of the enhanced frictional contact and decreased mechanical strength leads to the failure and wear of diamond. This work provides a novel insight into the wear mechanism of diamond under elevated temperatures, and contributes to the wear theory in diamond materials.