Molecular dynamics simulations of scratching characteristics in vibration-assisted nano-scratch of single-crystal silicon

Highlights: • In vibration-assisted scratch, the scratch forces fluctuate periodically. • Vibration rebalances the existing anisotropy among forces. • Vibration reduces the anisotropy of stress and thins the amorphous-layer. • Vibration suppresses the anisotropic deformation in machining of brittle materials. • There may be an optimal combination of amplitude and frequency. Vibration-assisted grinding improves machining quality and efficiency over conventional grinding, whereas its atomistic mechanism remains unclear. In this study, we investigated vibration-assisted machining using molecular dynamics simulations of the nano-scratching process by considering single-crystal silicon as the paradigm material. Vibration dynamically redistributes and rebalances the existing anisotropy among the applied forces, thereby leading to unique scratch characteristics including homogeneous deformation. Vibration reduces the tangential and normal force components and effectively suppresses the anisotropic stress state, resulting in a reduction of the amorphous-layer thickness and enlargement of the scratched surface area. The magnitudes of the tangential and normal components vary cyclically with a frequency that is twice that of the applied vibration. Furthermore, when the frequency increases, the tangential and normal components and amorphous-layer thickness decrease gradually, opposite to the scratched surface area. In addition, as the vibration amplitude increases, the tangential and normal components decrease, in contrast with the behaviour of the amorphous layer, which thins gradually and then slightly increased to a constant thickness. Vibration-assisted scratch effectively turns the brittle material at the working spot into a ductile material. Thus, our atomistic insights suggest a new route for optimization of vibration-assisted grinding processes.