Liu Yi, Chen Xuefei, Wei Kang, Xiao Lirong, Chen Bin, Long Haibo, Yu Yandong, Hu Zhaohua, Zhou Hao
Nano and Heterogeneous Material Center, School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, China.
State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China.
Materials (Basel). 2019 Apr 22;12(8):1307. doi: 10.3390/ma12081307.
Twinning structures and their interfacial segregation play a key role in strengthening of magnesium alloys. Micro-steps are frequently existed in the incoherent twin boundaries, while the effect of them on interface and interfacial segregation is still not clear. In this work, we performed an atomic-scale microstructure analysis using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) to explore the effect of micro-steps on twin and its interfacial segregation in Mg-Ag alloy. Diffraction pattern of the incoherent {10 1 ¯ 1} twin shows that the misorientation has a slight tilt of 5° from its theoretical angle of 125° due to the accumulated effects of the micro-steps and their misfit dislocations in twin boundaries. Most of the micro-steps in {10 1 ¯ 1} twin boundary are in the height of 2 d ( 10 1 ¯ 1 ) and 4 d ( 10 1 ¯ 1 ) , respectively, and both of them have two types according to whether there are dislocations on the micro-steps. The twin boundary is interrupted by many micro-steps, which leads to a step-line distributed interfacial segregation. Moreover, the Ag tends to segregate to dislocation cores, which results in the interruption of interfacial segregation at the micro-steps with dislocations.
孪晶结构及其界面偏析在镁合金强化中起着关键作用。非共格孪晶界中经常存在微台阶，但其对界面及界面偏析的影响尚不清楚。在本工作中，我们使用高角度环形暗场扫描透射电子显微镜（HAADF-STEM）进行了原子尺度的微观结构分析，以探究微台阶对Mg-Ag合金中孪晶及其界面偏析的影响。非共格{10 1 ¯ 1}孪晶的衍射花样表明，由于微台阶及其在孪晶界中的错配位错的累积效应，其取向差相对于理论角度125°有5°的轻微倾斜。{10 1 ¯ 1}孪晶界中的大多数微台阶分别处于2 d ( 10 1 ¯ 1 ) 和4 d ( 10 1 ¯ 1 ) 的高度，并且根据微台阶上是否存在位错，它们都有两种类型。孪晶界被许多微台阶打断，这导致了呈台阶线分布的界面偏析。此外，Ag倾向于偏聚到位错核心，这导致在有位错的微台阶处界面偏析中断。
