Size effects on dislocation starvation in Cu nanopillars : A molecular dynamics simulations study

Abstract: Size plays an important role on the deformation mechanism of nanopillars. With decreasing size, many FCC nanopillars exhibit dislocation starvation state which is responsible for their high strength. However, many details about the dislocation starvation mechanism like how often it occurs, and how much is its contribution to the total plastic strain, are still elusive. Similarly, the size below which the dislocation starvation occurs in the nanopillars is not clearly established. In this context, the atomistic simulations have been performed on the compressive deformation of $<$110$>$ Cu nanopillars with size (d) ranging from 5 to 21.5 nm. The molecular dynamics (MD) simulation results indicate that the nanopillars deform by the slip of extended dislocations and exhibit dislocation starvation mainly at small sizes ( $<$ 20 nm). The frequency of the occurrence of dislocation starvation is highest in small size nanowires and it decreases with increasing size. Above the nanopillar size of 20 nm, no dislocation starvation has been observed. Further, we define the dislocation starvation strain and based on this, it has been shown that, the contribution of dislocation starvation state to the total plastic strain decreases from 70\% in small size nanopillars to below 5\% in large size pillars. The present results suggest that the dislocation starvation is a dominant phenomena in small size nanopillars.