Grain boundaries dependence of plastic deformation in nanocrystalline Cu film investigated by phase field and molecular dynamics methods

Abstract

The phase filed model was used to create the nanocrystalline (NC) Cu film with more natural grain boundaries (GBs) for molecular dynamics (MD) simulation. The results obtained by using these methods are in good agreement with previous experimental results. In the NC Cu film, the plastic deformation is governed by the stacking faults (SFs) and deformation twinnings (DTs). DTs in NC Cu film have a great influence on the deformation behaviors of grains, which can make two adjacent grains merge into one larger grain, generate a new grain, and twist a grain. The model with average grain size (d) of 17.84 nm exhibits large flow stress and ductility because of the large fraction of hexagonal-close-packed (HCP) structures including SFs and twinning boundaries (TBs). Besides, the deformation of GBs in the 17.84 nm model is large, which can reduce the stress-concentration on the GBs and then results in delaying the generation of DTs. The deformation behavior of curved GBs in the initial tensile stage is that atoms migrate from face-centered cubic (FCC) structures to curved GBs along (111) surface, which is different from the shuffling motion of the flat GBs.