Investigate the mechanical property of nanopolycrystal silicon by means of the nanoindentation method

A comprehensive understanding of the basic deformation mechanisms is essential for novel nanomaterials with unique properties for engineering applications. Unfortunately, nanopolycrystal materials with smaller grains are difficult prepare, which makes the study of the deformation process difficult using experiments. The molecular dynamics (MD) method has already been proved to be an efficient tool kit for the nanoscale phenomenon and was gradually adopted by many researchers to investigate the mechanical deformation of nanocrystalline materials. This manuscript studies the mechanical response of specimens with internal grains separated by high angle boundaries without porosities and impurities using MD simulation methods. The results demonstrate that the partial dislocation activity takes over in nanocrystalline materials if the grain sizes are large enough. The distribution of the ideal crystal structure along the radial direction remains almost unchanged, which justifies that little lateral deformation is induced. The animation shows that many atoms are stripped by the feeding of the indenter. This type of atom removal (moves just like rain flow) is different from any kind of material stripping in the macroscopic scale. Therefore, the deformation of the substrate is generated by the coupling of dislocation and atom sliding. The distribution of dislocation is more suitable for characterizing materials deformation at small scale. In addition, a novel cone-shaped dislocation distribution is observed. With the feeding of tools, the amount of screw dislocation gradually increases while the amount of the edge dislocation gradually decreases. The simulation results also show that the grain boundary exhibits higher self-diffusivities than the perfect lattice, which is helpful in grain boundary sliding.