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

TL;DR

This study uses molecular dynamics simulations to explore how uniaxial strain induces phase transitions from bcc to hcp and fcc structures in iron, revealing orientation-dependent nucleation and growth behaviors.

Contribution

It provides detailed insights into the nucleation and growth mechanisms of hcp and fcc phases in bcc iron under high strain rates, highlighting orientation effects and intermediate structures.

Findings

Transition pressures are approximately 14 GPa for all orientations.

Mixed phase duration varies with loading direction, shortest for [011].

hcp nucleates first along [001], forming laminar structures.

Abstract

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.