The mechanism of plasticity and phase transition in iron single crystals under cylindrically divergent shock loading

Cylindrically divergent shock loading significantly influences the plasticity and phase transition of iron. In this study, the mechanisms of plasticity and α→ε phase transition are investigated using large-scale nonequilibrium molecular dynamics simulation. We find that iron undergoes a local bcc–hcp–bcc–hcp (bcc: body-centered cubic; hcp: hexagonal close-packed) phase transition under cylindrically divergent shock loading with cylinder axis lying in [001] and [110] directions. A bcc lattice reorientation driven by resolved shear stress occurs during the hcp–bcc reverse transition and results in bcc twins, which transform into hcp twin structures with an unexpected c-axis, as compared with planar shock. Moreover, we analyze the coupling behavior between plasticity and phase transition and find that collective movement and rearrangement of atoms induced by plastic slip on the shuffle plane play a key role in the activation of phase transition, which significantly differs from that of planar shock.