Metals containing abundant coherent twin boundaries (TBs) are able to sustain substantial plastic deformation without fracture due to shear-induced TB migration and sliding. Retaining ductility in these metals, however, has proven difficult because detwinning rapidly exhausts TB migration mechanisms at large deformation, whereas TB sliding was only evidenced for loading on very specific crystallographic orientations. Here, we reveal the intrinsic shear deformability of twins in nanocrystals using in situ nanomechanical testing and multiscale simulations and report extreme shear deformability through TB sliding up to 364%. Sliding-induced plasticity is manifested for orientations that are generally predicted to favor detwinning and shown to depend critically on geometric inhomogeneities. Normal and shear coupling are further examined to delineate a TB orientation-dependent transition from TB sliding to TB cracking. These dynamic observations reveal unprecedented mechanical properties in nanocrystals, which hold implications for improving metal processing by severe plastic deformation.

中文翻译：

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揭示金属纳米晶体中的极端双边界剪切变形性

由于剪切引起的 TB 迁移和滑动，含有大量共格孪晶界 (TB) 的金属能够承受大量塑性变形而不会断裂。然而，在这些金属中保持延展性已被证明是困难的，因为去孪晶会在大变形时迅速耗尽 TB 迁移机制，而 TB 滑动仅在非常特定的晶体取向上加载时得到证明。在这里，我们使用原位纳米力学测试和多尺度模拟揭示了纳米晶体中孪晶的固有剪切变形能力，并报告了通过 TB 滑动高达 364% 的极端剪切变形能力。滑动诱导的可塑性表现在通常被预测有利于去孪晶的方向上，并显示出严重依赖于几何不均匀性。进一步检查法向和剪切耦合以描绘从 TB 滑动到 TB 开裂的 TB 方向相关的过渡。这些动态观察揭示了纳米晶体前所未有的机械性能，这对通过严重的塑性变形改善金属加工具有重要意义。