Molecular dynamics analysis on the indentation hardness of nano-twinned nickel

Abstract

Molecular dynamics simulations were employed to perform the nanoindentation analysis of nanocrystalline nickel with a variety of crystal structures (single-crystal, polycrystalline, and nano-twinned) and twin layer thicknesses under an indenter of spherical shape. To understand the effects of crystal structure and twin spacing on nanoindentation responses, the indentation force, strain, atomic rearrangement, dislocation, temperature, hardness, Young's modulus and elastic recovery rate of the indentation region were analyzed. It was noted that the three types of nanocrystalline nickel's mechanical properties and elastic recovery rate were greatly affected by their crystal structures. The results show that the hardness of the nano-twinned nickel is negatively correlated with the thickness of the twin layer, and the maximum hardness is 18.1 GPa when the thickness of twin layer is 1.2 nm. For the three structures, in the width direction, the elastic recovery ratio of the nano-twin structure is the largest, and the elastic recovery ratio of the nanotwin structure in the depth direction is the smallest. In the single crystal structure, the compression area is concentrated under the indenter and distributed in a ' V ' shape, and in the polycrystalline and twin structures, the compression area is scattered. In the polycrystalline structure, the compression area were distributed below the indenter and at crystal boundaries. In the nano-twinned structure, the compression area were mainly distributed below the indenter.