Revealing shear-coupled migration mechanism of a mixed tilt-twist grain boundary at atomic scale
Revealing shear-coupled migration mechanism of a mixed tilt-twist grain boundary at atomic scale
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DOI：
10.1016/j.actamat.2023.119237
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发表时间：
2023-08
期刊：
影响因子：
9.4
通讯作者：
Zheng Fang;Boyang Li;Susheng Tan;S. Mao;Guofeng Wang
中科院分区：
文献类型：
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作者：
Zheng Fang;Boyang Li;Susheng Tan;S. Mao;Guofeng Wang
剪切耦合晶界迁移对纳米晶材料的塑性和蠕变抗力有很大影响。然而，到目前为止，一般混合倾斜-扭曲GBs(MGB)剪切耦合迁移背后的原子机制仍然很难捉摸。在这里，我们利用原位高分辨电子显微镜和分子动力学模拟技术，揭示了金纳米双晶在室温剪切变形过程中，典型的MGB，即<；001>；{200}/<；01>；{1‘11}Gb的原子尺度迁移行为。观察到了两种截然相反的剪切耦合因子的迁移模式，并进一步揭示了两种不同的迁移模式，它们是由具有不同晶体参数的GB断口的运动所介导的，并且表现出不同的晶格对应关系，即<；001>；{200}和<；001>；{020}-to-lt；01>；{111}。模拟结果证实，在不同的应力/应变状态下，这两种不同的迁移模式可以被激活。此外，在实验和模拟中都发现过多的GB滑动和GB平面重新定向可以适应GB迁移，这可能是因为在GB迁移过程中需要建立点对点晶格对应。这些发现为金属纳米晶的断裂迁移提供了原子尺度的实验证据，并阐述了迄今未见报道的金属纳米晶的复杂剪切响应，这对于通过控制金属纳米晶的迁移来优化金属纳米晶体的延展性具有重要意义。
Shear-coupled grain boundary (GB) migration greatly influences the plasticity and creep resistance of nanocrystalline materials. However, the atomistic mechanisms underlying the shear-coupled migration of general mixed tilt-twist GBs (MGBs) remain largely elusive to date. Here, using in-situ high-resolution transmission electron microscopy and molecular dynamics simulations, we uncover the atomic-scale migration behavior of a typical MGB, ie,< 001>{200}/< 0 1¯ 1>{1¯ 11} GB, during the room-temperature shear deformation of Au nano-bicrystals. Two distinct migration patterns showing the opposite signs of shear-coupling factor were observed and further revealed to be mediated by the motion of GB disconnections with different crystallographic parameters and exhibit different lattice correspondence relations, ie,< 001>{020}-to-< 0 1¯ 1>{200} and< 001>{020}-to-< 0 1¯ 1>{111}. Simulation results confirm that the two distinct migration patterns could be activated under different stress/strain states. Moreover, excess GB sliding and GB plane reorientation were found to accommodate the GB migration in both experiments and simulations, likely due to the necessity of establishing a point-to-point lattice correspondence during GB migration. These findings provide atomic-scale experimental evidence on the disconnection-mediated migration of MGBs and elaborate on the hitherto unreported complex shear response of MGBs, which have valuable implications for optimizing the ductility of metallic nanocrystals through controlling GB migration.