Extensive studies have been focused on improving the fatigue performance of materials, as fatigue fracture is a primary mode of failure in material applications for structural components. The introduction of high-density twins emerges as a novel strategy for enhancing fracture toughness; however, the mechanisms driving this enhancement during fatigue remain elusive. In this work, the impact of twins on fracture toughness in nanotwinned Cu was investigated with correlated transmission electron microscopy under cyclic loading. The results revealed three toughening mechanisms, i.e., bridging, bending of twin lamellae and ductile cracking along twin boundaries. The occurrence of the three toughening mechanisms strongly depends on twin thickness and cracking orientations, as different dislocation modes are activated in varying scenarios. Specifically, bridging and ductile cracking along twin boundaries are facilitated by the pile-up and continuous emission of hard mode I dislocations, respectively, while the bending of twin lamellae is governed by the accumulation of same-signed soft mode dislocations triggered by crack-tip stress. These findings unveil the underlying toughening mechanisms of twins in nanotwinned metals during cyclic loading and offer valuable guidance for the design of high-toughness nanolayered materials.

中文翻译：

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循环加载过程中孪晶对纳米孪晶Cu断裂的增韧作用


广泛的研究集中在提高材料的疲劳性能上，因为疲劳断裂是结构部件材料应用中的主要失效模式。高密度孪晶的引入成为增强断裂韧性的一种新策略；然而，在疲劳期间驱动这种增强的机制仍然难以捉摸。在这项工作中，利用相关透射电子显微镜在循环加载下研究了孪晶对纳米孪晶铜断裂韧性的影响。结果揭示了三种增韧机制，即孪晶片层的桥接、弯曲和沿孪晶边界的延性开裂。三种增韧机制的发生很大程度上取决于孪晶厚度和裂纹方向，因为在不同的情况下会激活不同的位错模式。具体来说，沿着孪晶边界的桥接和延性裂纹分别是由硬模式 I 位错的堆积和连续发射促进的，而孪生片层的弯曲则由裂纹尖端触发的同符号软模式位错的积累控制。压力。这些发现揭示了循环加载过程中纳米孪晶金属中孪晶的潜在增韧机制，并为高韧性纳米层材料的设计提供了有价值的指导。