Department of Physics, King's College London, London, WC2R 2LS, UK.
Department of Materials Science and Engineering, University of Sheffield, Sheffield, S1 3JD, UK.
Sci Rep. 2023 Mar 8;13(1):3861. doi: 10.1038/s41598-023-30880-w.
Twin boundaries have been shown to deviate from the twinning planes in hcp metals, and facets have often been observed in twin interfaces. This study presents a twinning disconnection-based model for faceting in single, double and triple twin boundaries in magnesium. Primary twinning disconnections predicted via symmetry arguments are shown to produce commensurate facets in single twin boundaries, which are then transformed into commensurate facets in double twin boundaries via the action of secondary twinning disconnections. In contrast, it is shown that for triple twin boundaries with tension-compression-tension twinning sequence, no commensurate facets can be produced by the action of tertiary twinning disconnections. The effect of facets on the macroscopic orientation of twin interfaces is discussed. Theoretical findings are validated by a transmission electron microscopy study of a hot rolled Mg-1.18wt%Al-1.77wt%Nd alloy. Single and double twins are observed, as well as rare triple twins, and the interface between the matrix and a triple twin is captured for the first time. Facets consistent with theoretical predictions are imaged via high-resolution TEM and macroscopic deviations of the boundaries from the primary twinning planes are measured.
孪晶界已被证明在 hcp 金属中偏离孪生面，并且在孪晶界面上经常观察到小平面。本研究提出了一种基于孪晶断开的模型，用于研究镁中单、双和三孪晶界中的小平面化。通过对称论证预测的主要孪晶断开被证明会在单孪晶界中产生共格小平面，然后通过次级孪晶断开的作用转化为双孪晶界中的共格小平面。相比之下，对于具有拉伸-压缩-拉伸孪生序列的三孪晶界，通过三级孪晶断开的作用不能产生共格小平面。讨论了小面对孪晶界面宏观取向的影响。理论结果通过对热轧 Mg-1.18wt%Al-1.77wt%Nd 合金的透射电子显微镜研究得到了验证。观察到了单孪晶和双孪晶，以及罕见的三孪晶，并且首次捕获到了基体和三孪晶之间的界面。通过高分辨率 TEM 成像观察到与理论预测一致的小平面，并测量了边界相对于初级孪生面的宏观偏差。
