Effects of vacancies on plasticity and phase transformation in single-crystal iron under shock loading

Abstract

A characteristic region with vacancy concentration ranging from 0% to 2% was introduced into the single-crystal iron to investigate the effects of vacancies on plasticity and phase transformation of single-crystal iron under shock loading. The simulations were implemented by applying non-equilibrium molecular dynamics simulations with an excellent modified analytic embedded-atom method (MAEAM) potential. A fixed piston velocity of vp = 0.5 km/s was applied in our simulations, under which no plasticity or phase transformation occurred in the perfect single-crystal iron based on the description of the used MAEAM potential. The plasticity and phase transformation in iron were observably influenced by the vacancies as shown in this work. Significant anisotropy of shock response was distinctly exhibited. The nucleation and growth of dislocation loops emitting from the vacancy region were clearly observed in the sample that was shocked along the [110] direction, and the activated slip systems were determined as (112¯)[111] and (112)[111¯]. The vacancies and the vacancies-induced dislocation loops provided preferential nucleation positions for the subsequent phase transformation, which resulted in the phenomenon that the phase transformation product (HCP phase) always preferentially appeared in the vacancy region. The influences of different vacancy concentrations on plasticity and phase transformation were also discussed.