Abstract Understanding the deformation mechanisms of hexagonal close-packed (HCP) polycrystals at the grain scale is crucial for developing both macro and micro scale predictive models. Slip and twinning are the two main deformation mechanisms of HCP polycrystals at room temperature. In this paper, the development of grain-level stress tensors during nucleation and growth of twins is investigated. A pure zirconium specimen with HCP crystals is deformed in-situ while the centre-of-mass, orientation, elastic strain, and stress of individual grains are measured by three-dimensional synchrotron X-ray diffraction (3D-XRD). The observed microstructure is subsequently imported into a crystal plasticity finite element (CPFE) model to simulate the deformation of the polycrystal. The evolution of stress in twin-parent pairs at the early stages of plasticity, further into plasticity zone, and unload is studied. It is shown that twins do not relax very much at the nucleation step, but the difference between the measured stress in the twin and parent increases further into plastic zone where twins relax. While at the early stages of plasticity all six twin variants are active, a slightly better estimation of active variants is obtained using the measured grain-resolved stress tensors.

中文翻译：

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塑性早期变形孪晶的形核

摘要 了解六方密堆积 (HCP) 多晶在晶粒尺度上的变形机制对于开发宏观和微观尺度预测模型至关重要。滑移和孪晶是 HCP 多晶在室温下的两种主要变形机制。在本文中，研究了孪晶的成核和生长过程中晶粒级应力张量的发展。具有 HCP 晶体的纯锆样品在原位变形，同时通过三维同步辐射 X 射线衍射 (3D-XRD) 测量单个晶粒的质心、取向、弹性应变和应力。随后将观察到的微观结构导入晶体塑性有限元 (CPFE) 模型以模拟多晶的变形。可塑性早期双亲对应力的演变，进一步进入塑性区，并研究卸载。结果表明，孪晶在成核步骤中并没有非常松弛，但是孪晶和母体中测得的应力之间的差异进一步增加到孪晶松弛的塑性区。虽然在塑性的早期阶段，所有六个孪生变体都是活跃的，但使用测量的晶粒分辨应力张量获得了对活跃变体的稍微更好的估计。