Topological model of type II deformation twinning
Topological model of type II deformation twinning
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DOI：
10.1016/j.actamat.2018.03.014
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发表时间：
2018-06
期刊：
影响因子：
9.4
通讯作者：
R. Pond;J. Hirth
中科院分区：
文献类型：
--
作者：
R. Pond;J. Hirth
用界面缺陷和界面结构的拓扑理论描述了II型孪晶的形成和生长模型。I型孪晶通过断开回路的产生和扩展形成并增长到宏观维度，前提是这些缺陷具有足够的移动性。然而，如果它们的流动性有限，它们就会聚集成一堵倾斜的墙，在调节松弛后，形成第二类共轭双胞胎。因此，无论是I型还是II型共轭双胞胎形式都是竞争机制的结果，主要取决于断链的流动性。参考α−U中孪生的实验观察，讨论了该模型的合理性。与{1 3‘0}复合孪晶中预期的较高的断裂迁移率相比，在“{17 6’}”和“{1 7‘2}”II型孪晶中，断连迁移率受到原子洗牌的限制。在拓扑模型中，孪生剪切量与经典变形孪生模型的预测值相同。然而，由于滑动面上的分离运动，I型孪生直接由剪切形成，而II型孪生的机制不同，不仅涉及通过分离运动的剪切，而且还涉及调节松弛。这种理解促使人们重新评估经典几何方法中孪生元素的物理意义。
A model for the formation and growth of type II twins is described using the topological theory of interfacial defects and interface structures. A type I twin forms and grows to macroscopic dimensions by the generation and expansion of disconnection loops, provided these defects are sufficiently mobile. However, if their mobility is limited, they accumulate into a tilt wall, which, after accommodational relaxation, forms the type II conjugate twin. Thus, whether the type I or type II conjugate twin forms is the outcome of competitive mechanisms, depending primarily on disconnection mobility. The plausibility of this model is discussed with reference to experimental observations of twinning in α− U. Disconnection mobility is shown to be limited by atomic shuffling in the cases of"{17 6¯}" and"{1 7¯ 2}" type II twins, as compared with the higher mobility expected for the active disconnections in {1 3¯ 0} compound twins. In the topological model, the twinning shears are identical to those predicted by the classical model of deformation twinning. However, while type I twins are formed directly by shear due to the motion of disconnections on their glide planes, the mechanism of type II twinning is different, involving not only shear by disconnection motion but also accommodational relaxation. This understanding prompts a reassessment of the physical significance of the twinning elements of the classical geometrical approach.