A half-shear-half-shuffle mechanism and the single-layer twinning dislocation for {112¯2}〈112¯3¯〉 mode in hexagonal close-packed titanium
A half-shear-half-shuffle mechanism and the single-layer twinning dislocation for {112¯2}〈112¯3¯〉 mode in hexagonal close-packed titanium
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DOI：
10.1016/j.actamat.2021.117150
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发表时间：
2021-09
期刊：
影响因子：
9.4
通讯作者：
Jingwei Li;Manling Sui;Bin Li
中科院分区：
文献类型：
--
作者：
Jingwei Li;Manling Sui;Bin Li
在六方密排 (HCP) 金属的孪生模式中，{11 2´ 2}< 11 2´ 3´> 模式的机制特别令人困惑和有争议。文献报道中，存在三种可能的第二不变面，即{11 2´ 2}< 11 2´ 3´>孪生模式的K 2 面：{11 2´ 4´}已被广泛接受，对应于三层带状孪晶位错；{11 2´ 2´}被认为是不利的；和（0002）仅在原子模拟中观察到，对应于单层孪晶位错。{11 2´ 4´}是由经典孪晶理论预测的，实验测量的钛和锆中孪晶剪切 s 的大小似乎与预测非常吻合。然而，{11 2´ 4´} 从未在模拟中得到验证，表明 (0002) 应该是 K 2 平面。由于缺乏对孪晶位错结构的实验观察，这一冲突尚未得到解决。在这项工作中，通过扫描透射电子显微镜（STEM）观察，结合原子模拟，在原子尺度上解析变形纯钛中的孪晶边界结构。原子分辨率STEM明确表明孪晶位错仅涉及单个孪晶面，K 2 面为(0002)，这与原子模拟一致。 STEM结果还揭示了半剪切半洗牌过程，其表现为单层孪晶位错滑移产生的独特孪晶边界结构。为了解释这些结果，我们对所有三个 K 2 平面的晶格对应进行了详细检查。特别是，在经典理论框架内分析了晶格变换中所需的剪切和洗牌。这些分析很好地解释了为什么(0002)是比{11 2´ 4´}和{11 2´ 2´}更有利的K 2 平面，并妥善解决了经典孪生理论的预测与模拟结果之间的冲突。
Among the twinning modes in hexagonal close-packed (HCP) metals, the mechanism for {11 2¯ 2}< 11 2¯ 3¯> mode is particularly confusing and controversial. In the literature reports, there are three possible second invariant planes, ie the K 2 planes for {11 2¯ 2}< 11 2¯ 3¯> twinning mode:{11 2¯ 4¯} which has been widely accepted and corresponds to a three-layer zonal twinning dislocation;{11 2¯ 2¯} that is deemed unfavorable; and (0002) which has only been observed in atomistic simulations and corresponds to a single-layer twinning dislocation.{11 2¯ 4¯} was predicted by classical twinning theory and the experimentally measured magnitude of twinning shear s in titanium and zirconium seemed to agree well with the prediction. However,{11 2¯ 4¯} has never been verified in simulations which show that (0002) should be the K 2 plane. This conflict has not been resolved due to the lack of experimental observation of the structure of twinning dislocations. In this work, scanning transmission electron microscopy (STEM) observations are conducted to resolve the twin boundary structure in deformed pure titanium on the atomic scale, combined with atomistic simulations. Atomic resolution STEM unambiguously shows that the twinning dislocation only involves a single twinning plane and the K 2 plane is (0002), which is consistent with the atomistic simulations. The STEM results also reveal a half-shear-half-shuffle process which is manifested by a unique twin boundary structure generated by the glide of single-layer twinning dislocations. To explain these results, the lattice correspondences of all three K 2 planes are examined in great detail. In particular, shear and shuffle required in the lattice transformations are analyzed inside the framework of classical theory. These analyses explain well why (0002) is the more favorable K 2 plane than {11 2¯ 4¯} and {11 2¯ 2¯}, and properly resolve the conflict between the prediction of the classical twinning theory and the simulation results.