Atomistic simulation of martensitic transformations in zirconium nanoclusters

Molecular dynamics simulation has been applied to the study of martensitic transformations in nanoclusters of pure zirconium containing slightly in excess of two million atoms. Starting structures of both single crystal and polycrystalline samples were prepared in the bcc phase by solidification from the liquid. Continuous cooling simulations into the hcp α′ were conducted at various quench rates revealing a decrease in martensitic start temperature with increasing rate. The temperature dependence appears consistent with previously published models for heterogeneous nucleation. The phase transformation is found to initiate at the cluster surface in the single crystal (bcc) clusters, but starts at the grain boundaries in the polycrystals. The start temperature for the polycrystals is slightly higher than that for single crystal clusters quenched at the same rate.