Study of effect of indenter shape in nanometric scratching process using molecular dynamics

In this paper three-dimensional molecular dynamics (MD) simulations are performed to investigate the effect of indenter shape on the nanometric scratching process of copper. In the simulations two types of indenters (sharp and blunt) are used to study the effect of indenter shape on the workpiece deformation and friction. The results show that indenter shape significantly affects the nanoscratch deformation. The blunt indenter causes larger deformation region and much more dislocations at both the indentation and scratch stages. During the scratching stage the blunt indenter results in larger chip volume in front of the indenter. The results also show that there is a size effect on how the indenter shape influences the nanometric scratching process. For small indenters (radius of 1.9 nm) the blunt indenter may result in bigger friction coefficient than the sharp indenter, while for bigger indenters (radii of 3 nm and 4.5 nm) it is reversed. The simulation results indicate that generally the sharp surface asperities in MEMS cause more friction. However, when the asperities are rather small, the blunt asperities may result in more friction. Furthermore, both the friction coefficient and scratch hardness decrease with the increase of the radius of the blunt indenter.