Strain-Rate Dependence of Plasticity and Phase Transition in [001]-Oriented Single-Crystal Iron

Non-equilibrium molecular dynamics simulations have been used to investigate strain-rate dependence of plasticity and phase transition in [001]-oriented single-crystal iron under ramp compression. Here, plasticity is governed by deformation twinning, in which kinetics is tightly correlated with the loading rate. Over the investigated range of strain rates, a hardening-like effect is found to shift the onset of the structural bcc-to-hcp phase transformation to a high, almost constant stress during the ramp compression regime. However, when the ramp evolves into a shock wave, the bcc-hcp transition is triggered whenever the strain rate associated with the plastic deformation reaches some critical value, which depends on the loading rate, leading to a constitutive functional dependence of the transition onset stress on the plastic deformation rate, which is in overall consistence with the experimental data under laser compression.