An atomic study on the shock-induced plasticity and phase transition for iron-based single crystals

The martensitic phase transition α → ε of iron is of particular interest to researchers and industrialists due to its technological and scientific significance in recent decades. Experimental and numerical studies have discovered and confirmed the phase transition mechanisms under shock loading. However, the relation between plasticity and the phase transition, which is of key importance in understanding the material behavior under dynamic loading, has not been made clear, and former NEMD simulations fail to reproduce the plasticity observed in experiments. In this work, a new embedded-atom-model potential for iron has been developed and validated. Large-scale NEMD simulations are performed with a variety of loading strengths along three low index crystallographic directions, i.e., [0 0 1], [1 1 0] and [1 1 1], and the phase transition mechanism is examined with the aid of the c axis analysis technique proposed in this work. The differences in shock response to the different loading directions are explained by rotation symmetry and compression mechanisms as the first step toward phase transformation of iron. Although no well-defined plastic process is observed for the shock along the [1 0 0] and [1 1 1] directions, nucleation, propagation and multiplication of dislocations are clearly observed, and the slip system associated with plastic slip is determined to be {1 1 2} 〈1 1 1〉 when loading along the [1 1 0] direction.