Atomic-scale simulations of nanoscratching behavior on copper coated with multilayer WSe₂

WSe₂ exhibits excellent potential for reducing friction and resisting wear, making it suitable for application as a solid lubricant. In this study, the tribological properties of Cu coated with WSe₂ layers of varying thicknesses were investigated via nanoscale molecular dynamics simulations. Indentation tests were conducted on WSe₂-coated Cu with 0–3 layers to explore its mechanical response. Additionally, scratching processes at different indentation depths were performed, and the nanoscale friction morphology, mechanical response, defect propagation, and stress distribution were analyzed. The simulation results indicate that during the indentation process, the protective effect of WSe₂ coatings enhances with an increase in the number of layers. During scratching at small indentation depths, multilayer WSe₂ enables stick-slip friction to persist to a greater indentation depth as the number of WSe₂ layers increases. At relatively large scratching depths, an increase in the number of layers leads to initial fracture of the top atomic layer; due to stress release, the bottom WSe₂ layer undergoes rebound, which mitigates the impact of plastic damage on the Cu substrate. Furthermore, the failure mode of the topmost WSe₂ layer differs between monolayer and multilayer systems: in monolayer systems, WSe₂ mainly fails via zigzag-direction crack propagation and wrinkle formation; in multilayer systems, it tends to fracture into debris, as the interlayer interaction is stronger than that at the WSe₂/Cu interface. This work provides important theoretical support for the design of wear-resistant WSe₂ coatings, which are expected to be applied to small-scale components in micro/nanoelectromechanical systems (MEMS/NEMS).