论文部分内容阅读
尽管对镁合金中变形孪晶的形成及结构已有大量研究报道,但目前为止对非常规的高指数型孪晶的形成及结构本质特征的了解却仍十分有限。本研究利用透射电子显微镜(TEM)对室温压缩变形的Mg-Y1.1-Nd0.4-Zn0.8(%,原子分数)合金进行了详细的结构表征,结果发现在10%的变形量下该合金中可以形成罕见的{1015}型高指数孪晶带。该类型孪晶带界面取向与理论上的{1015}孪晶界面并不一致,而是近似平行于基体{1011}晶面。在{1015}孪晶板条内可以观察到{1012}二次孪生开动的特征,同时也证实了孪晶板条内存在小角度的晶格取向调整。利用二次孪生加小角度晶格扭转机制可以很好的解释这种孪晶带的形成过程。基于该种机制及晶体学孪生几何分析预测镁合金中其他可能出现的高指数型孪晶带有{1016},{2021},{3031}以及{3032}。通过这种机制形成的高指数孪晶带是表观上与一次孪晶带形貌相似的特殊变形带,其与基体的界面取向应与一次孪晶界面一致。
Although a great deal of research has been reported on the formation and structure of deformed twins in magnesium alloys, the understanding of the formation and structure of unconventional high-index twins has so far been limited. In this study, TEM was used to characterize the structure of Mg-Y1.1-Nd0.4-Zn0.8 (%, atomic fraction) alloy under compressive deformation at room temperature. It was found that at 10% deformation In this alloy, a rare {1015} type high index twin band can be formed. The twin interface orientation is not consistent with the theoretical {1015} twin interface but approximately parallel to the {1011} crystal face of the substrate. The {1012} secondary twin-on feature was observed in the {1015} twinned lamellae and also confirmed the existence of small-angle lattice orientation adjustments in the twinned lamellae. The use of twin twisting plus a small angle lattice twist mechanism can well explain the formation of twin bands. Based on this kind of mechanism and crystal twinning geometry analysis, it is predicted that other possible high-index twins in magnesium alloys are {1016}, {2021}, {3031} and {3032}. The high-index twins formed by this mechanism are special deformation bands that are apparently similar to those of the primary twins. Their interfacial orientation with the matrix should be consistent with the one-twins interface.