Molecular dynamics study of hcp/fcc nucleation and growth in bcc iron driven by uniaxial strain

Molecular dynamics simulations are performed to investigate the structural phase transition in body-centered cubic (bcc) single crystal iron under high strain rate loading. We study the nucleation and growth of the hexagonal-close-packed (hcp) and face-centered-cubic (fcc) phases, and their crystal orientation dependence. Results reveal that the transition pressures are less dependent on the crystal orientations ($\mathtt{\sim}$14 GPa for loading along [001], [011], and [111] directions). However, the pressure interval of mixed phase for [011] loading is much shorter than loading along other orientations. And the temperature increased amplitude for [001] loading is evidently lower than other orientations. The hcp/fcc nucleation process is presented by the topological medium-range-order analysis. For loading along [001] direction, we find that the hcp structure occurs firstly and grows into laminar morphology in the (011)$_{\text{bcc}}$ planes with a little fcc atoms as intermediate structure. For loading along [011] and [111] directions, both the hcp and fcc structures nucleation and growth along the \{110\}$_{\text{bcc}}$ planes are observed, whose morphology is also discussed.

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