Size effects on dislocation starvation in Cu nanopillars: a molecular dynamic simulations study

Size plays an important role on the deformation mechanism of nanopillars. With decreasing size, many FCC nanopillars exhibit dislocation starvation which is responsible for their high strength. However, many details about the dislocation starvation 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 is not clearly established. In this context, atomistic simulations have been performed on the compression of <110> Cu nanopillars with size (d) ranging from 5 to 21.5 nm. 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-sized nanowires and it decreases with increasing size. Above the size of 20 nm, no dislocation starvation has been observed. Furthermore, we define the dislocation starvation strain and based on this, it has been shown that the contribution of the dislocation starvation to the total plastic strain decreases from 70% in small-sized nanopillars to below 5% in large-sized pillars. The present results suggest that dislocation starvation is a dominant phenomenon in small-sized nanopillars.