ABSTRACT Extensive experiments have shown that stress-assisted nanograin rotation is an important grain-boundary-mediated deformation mode in nanocrystalline materials. The nanograin rotation is observed to has close correlation with the enhanced dislocation activity and plasticity in nanocrystalline metals and alloys. However, how nanograin rotation affects the dislocation behaviour remains unclear. In the present study, a theoretical model is proposed to investigate the dislocation emission behaviour in nanocrystalline face-centered cubic crystals as nanograin rotation dominates the deformation. The energy characteristics and the critical shear stress that is required to trigger the dislocation emission from grain boundaries are analysed. The results show that the nanograin rotation process can make the originally energetically unfavourable dislocation emission process favourable. The critical stress can also be extraordinarily reduced as compared with the rotation-free case. As a result, the proposed dislocation emission process can reduce the required external stress to almost zero if the rotation magnitude can reach 8.5 and 2.9 degrees for Al and Pt, respectively. The findings suggest nanograin rotation as an effective dislocation-emission mechanism in nanocrystalline materials and possibly explain the experimentally observed rotation-dislocation correlation in nanocrystalline materials.

中文翻译：

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应力辅助晶粒旋转诱导纳米晶面心立方金属晶界位错发射

摘要 大量实验表明，应力辅助纳米晶粒旋转是纳米晶材料中一种重要的晶界介导变形模式。观察到纳米晶粒旋转与纳米晶金属和合金中增强的位错活性和塑性密切相关。然而，纳米晶粒旋转如何影响位错行为仍不清楚。在本研究中，提出了一个理论模型来研究纳米晶面心立方晶体中的位错发射行为，因为纳米晶粒旋转主导变形。分析了触发晶界位错发射所需的能量特性和临界剪切应力。结果表明，纳米晶粒旋转过程可以使原本在能量上不利的位错发射过程变得有利。与无旋转情况相比，临界应力也可以显着降低。因此，如果 Al 和 Pt 的旋转幅度分别达到 8.5 度和 2.9 度，则所提出的位错发射过程可以将所需的外部应力降低到几乎为零。这些发现表明纳米晶粒旋转是纳米晶材料中有效的位错发射机制，并可能解释了实验观察到的纳米晶材料中的旋转位错相关性。如果 Al 和 Pt 的旋转幅度分别达到 8.5 度和 2.9 度，则所提出的位错发射过程可以将所需的外部应力降低到几乎为零。这些发现表明纳米晶粒旋转是纳米晶材料中有效的位错发射机制，并可能解释了实验观察到的纳米晶材料中的旋转位错相关性。如果 Al 和 Pt 的旋转幅度分别达到 8.5 度和 2.9 度，则所提出的位错发射过程可以将所需的外部应力降低到几乎为零。这些发现表明纳米晶粒旋转是纳米晶材料中有效的位错发射机制，并可能解释了实验观察到的纳米晶材料中的旋转位错相关性。