Molecular dynamics simulation of effect of indenter shape on nanoscratch of Ni

Thin films of Ni and Ni alloy have been widely used in microelectromechanical systems (MEMS) and magnetic storage systems. As the dimensions of components in these systems decrease to the micro-scale, even the nano-scale, the interfacial phenomena significantly differ to the counterparts on the macro-scale. A better understanding of micro-/nano-tribology will benefit the fabrication of the small components. In this manuscript parallel molecular dynamics (MD) simulations have been conducted to investigate the nanoscratch behavior of nickel. The simulations are performed for two cases with different indenter shapes. Case I has a sharp indenter, while the indenter in Case II is blunt. It has been found that the indenter shape significantly influences the nanoscratch deformation. The sharp indenter only generates a small deformation area under the indenter, while the blunt one produces more dislocations and larger deformation area in the substrate. The simulation results show that the vertical forces during scratch in Case I are larger than those in Case II, while the scratching forces are similar in both cases during scratch. In addition, the sharp indenter has smaller indentation hardness than the blunt indenter. However, the blunt indenter exhibits smaller scratch hardness and smaller ratio of the scratching force to the vertical force. In order to improve the thermal stability, an algorithm has been proposed to dynamically determine the time-step of MD simulation, by which the system temperature can be maintained within a small range without thermostat layers.