Nanoindentation response of nanocrystalline copper via molecular dynamics: Grain-size effect

This paper is aimed at investigating the mechanical properties and deformation mechanisms of nanocrystalline copper under nanoindentation. The Voronoi tessellation method is adopted to generate nanocrystalline structures with stochastic grain orientations that mimic those in experiments. Grain-size effect is studied and discussed via molecular dynamics simulations. The results reveal the inversion of Hall-Petch relation about hardness at a grain size of 15.1 rim, which agrees well with previous works in tension. Below the critical grain size, grain boundary sliding, grain growth and grain rotation are easily observed. Grain boundary motion is the dominant deformation with smaller grain size below 15.1 nm while dislocation motion dominates above the critical value. It is noteworthy that the elastic recovery in indentation direction, increases with larger grain size and mono-crystalline copper behaves with the strongest elastic recovery. The study further reveals the deformation mechanism of nanocrystalline copper under nanoindentation and accelerates the functional applications of nanocrystalline materials.