Disconnection-Mediated Twin Embryo Growth in Mg
Disconnection-Mediated Twin Embryo Growth in Mg
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DOI：
10.2139/ssrn.3465850
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发表时间：
2019-09
期刊：
影响因子：
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通讯作者：
Yang Hu;V. Turlo;I. Beyerlein;S. Mahajan;E. Lavernia;J. Schoenung;T. Rupert
中科院分区：
文献类型：
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作者：
Yang Hu;V. Turlo;I. Beyerlein;S. Mahajan;E. Lavernia;J. Schoenung;T. Rupert
虽然六方密排金属的变形孪生由于其对机械性能的重大影响而得到了广泛的研究，但仍然缺乏对与孪晶胚胎生长相关的详细原子过程的了解。通过对镁进行分子动力学模拟，我们发现基底-棱柱界面发出的孪生断开的传播控制着孪生边界运动，并且是孪生胚胎初始生长过程中的限速机制。断开传播所需的时间与孪晶尖端之间的距离有关，间隔较宽的孪晶尖端需要更多时间来完成单位孪晶边界迁移事件。因此，本文提出了一种现象学模型，它统一了断开和双胞胎尖端传播两个过程，以提供双胞胎胚胎生长的定量分析。该模型很好地拟合了仿真数据，提取了两个关键参数（孪生尖端速度和孪生断开速度）。此外，还观察到孪晶断开速度与孪晶尖端速度之比与所施加的剪切应力之间存在线性关系。使用最近文献中纳米级单晶孪生生长的例子，我们发现我们的分子动力学模拟和分析模型与实验数据非常吻合。
While deformation twinning in hexagonal close-packed metals has been widely studied due to its substantial impact on mechanical properties, an understanding of the detailed atomic processes associated with twin embryo growth is still lacking. Conducting molecular dynamics simulations on Mg, we show that the propagation of twinning disconnections emitted by basal-prismatic interfaces controls the twin boundary motion and is the rate-limiting mechanism during the initial growth of the twin embryo. The time needed for disconnection propagation is related to the distance between the twin tips, with widely spaced twin tips requiring more time for a unit twin boundary migration event to be completed. Thus, a phenomenological model, which unifies the two processes of disconnection and twin tip propagation, is proposed here to provide a quantitative analysis of twin embryo growth. The model fits the simulation data well, with two key parameters (twin tip velocity and twinning disconnection velocity) being extracted. In addition, a linear relationship between the ratio of twinning disconnection velocity to twin tip velocity and the applied shear stress is observed. Using an example of twin growth in a nanoscale single crystal from the recent literature, we find that our molecular dynamics simulations and analytical model are in good agreement with experimental data.