Abstract:To study the effect of grain size on the mechanical properties and deformation mechanism of polycrystalline copper during the nanoindentation process, a large-scale molecular dynamics simulation model of polycrystalline copper is structured by Poisson-Voronoi method and Monte Carlo method. Based on the Hall-Petch relationship of the nanocrystalline copper, the single-crystalline and polycrystalline copper nanoindentation simulation models with different grain size are established. The nanoindentation process with different grain size are simulated by molecular dynamics method, and the nanoindentation force, internal stress and atomic potential energy of the atoms are calculated. Centrally symmetric parameter method is used to analyze the dislocation nucleation and propagation process in the surface and subsurface of the polycrystalline copper. The results show that the indentation force of single-crystalline copper is higher than that of polycrystalline copper, with the decrease of grain size, that of polycrystalline copper continuously decreases due to softening phenomenon. The high internal stress and atomic potential energy under the indenter leads to the defect evolution region under the indenter. The range of horizontal distribution of defects is larger than that of the vertical distribution, and such defects are limited in the grains around the indenter due to grain boundary network. The internal stress and atomic potential energy in polycrystalline copper with smaller grain size is larger than that with higher grain size, and the stress and potential energy in single-crystalline copper are lowest. Hence, during the nanoindentation process of polycrystalline copper, to improve the mechanical properties and deformation mechanism of nanocrystalline materials, it is suggests to adopt the nanocrystalline materials with grain size gradient.
