Abstract The plastic deformation of polycrystalline metals at high strain rates is controlled by the way defects (dislocations and twins) nucleate, propagate, and interact in the microstructure. To-date, the role of these defects has been estimated based on dynamic mechanical measurements coupled with ex situ investigations of the deformed microstructure. However, such investigations are fundamentally limited in their ability to characterize transient mechanisms. Here, we present for the first time direct, experimental observations of the nucleation, motion, and interaction of defects and cracks during deformation of pure copper at strain rates between 103 and 104 s−1. These observations are enabled by coupling a custom-built in situ high-rate straining stage with nanosecond-resolution dynamic transmission electron microscopy. The results show that while twins play only a minor role in the deformation of copper at quasi-static strain rates, the twin nucleation rate increases markedly at high strain rates. The preferred nucleation sites for twins also change, and the new twin interfaces become preferential paths for crack propagation, facilitating fracture through the original grains.

中文翻译：

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纯铜高应变率变形和断裂的原位 TEM 观察

摘要 多晶金属在高应变率下的塑性变形是由缺陷（位错和孪晶）在微观结构中成核、传播和相互作用的方式控制的。迄今为止，这些缺陷的作用是基于动态机械测量以及变形微观结构的非原位调查来估计的。然而，此类研究在表征瞬态机制的能力方面从根本上受到限制。在这里，我们首次对纯铜在 103 到 104 s-1 之间的应变速率变形过程中的形核、运动以及缺陷和裂纹的相互作用进行了直接的实验观察。这些观察是通过将定制的原位高速应变台与纳秒分辨率动态透射电子显微镜相结合来实现的。结果表明，虽然孪晶在准静态应变率下对铜变形的影响很小，但在高应变率下孪晶形核率显着增加。孪晶的首选成核位置也发生了变化，新的孪晶界面成为裂纹扩展的优先路径，促进了原始晶粒的断裂。