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

The martensitic phase transition alpha -> epsilon a 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., [001], [110] and [111], 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 [100] and [111] directions, nucleation, propagation and multiplication of dislocations are clearly observed, and the slip system associated with plastic slip is determined to be {112} < 111 > when loading along the [110] direction. (C) 2014 Elsevier Ltd. All rights reserved.

近几十年来，铁的马氏体相变α→ε′因其在技术和科学上的重要性，引起了研究人员和工业界的特别关注。实验和数值研究已经发现并证实了冲击加载下的相变机制。然而，塑性与相变之间的关系（这对于理解动态加载下的材料行为至关重要）尚未明确，而且以前的非平衡分子动力学（NEMD）模拟未能重现实验中观察到的塑性。在这项工作中，开发并验证了一种新的铁的嵌入原子模型势。沿着三个低指数晶体学方向，即[001]、[110]和[111]，用各种加载强度进行了大规模的非平衡分子动力学模拟，并借助本文提出的c轴分析技术研究了相变机制。作为铁相变的第一步，通过旋转对称性和压缩机制解释了不同加载方向上冲击响应的差异。尽管在沿[100]和[111]方向的冲击中没有观察到明确的塑性过程，但清楚地观察到了位错的形核、传播和增殖，并且当沿[110]方向加载时，确定与塑性滑移相关的滑移系为{112}<111>。（C）2014爱思唯尔有限公司。保留所有权利。