Shear-assisted grain coarsening in colloidal polycrystals
Shear-assisted grain coarsening in colloidal polycrystals
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DOI：
10.1073/pnas.2013456117
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发表时间：
2020-09-29
影响因子：
11.1
通讯作者：
Han, Yilong
中科院分区：
文献类型：
--
作者：
Li, Wei;Peng, Yi;Han, Yilong
剪切退火条件下的晶粒长大是控制多晶材料性能的关键。然而，它们的微观动力学还没有得到很好的理解，因为单个原子的轨迹很难跟踪。在这里，我们使用视频显微镜研究胶体多晶体中的单颗粒动力学的晶粒生长。在三种剪切状态下，均出现了丰富的晶粒长大现象，包括弱剪切下的正常晶粒长大和强剪切下的熔融-再结晶过程。对于中等剪切，早期的NGG被建立应力阻止，并最终让位于动态异常晶粒长大（DAGG）。我们发现，DAGG发生通过熔化-再结晶过程，这自然解释了令人困惑的应力降在DAGG的金属开始。此外，我们可视化的晶界（GB）迁移耦合剪切通过断开滑动。解决了分离-滑动动力学和周围粒子的集体运动问题。我们还观察到，晶粒旋转可以违反传统的关系R x B =常数（R是晶粒半径，和B是两个晶粒之间的取向差角）的发射和湮灭的位错穿过晶粒，导致在一个步进旋转。除了晶粒生长，我们发现在剪切诱导熔化的结果：熔融体积分数正弦变化的角度之间的不匹配的三角形晶格取向的晶粒和剪切方向。这些发现有可能为多晶材料的微结构工程提供信息。
Grain growth under shear annealing is crucial for controlling the properties of polycrystalline materials. However, their microscopic kinetics are not well understood because individual atomic trajectories are difficult to track. Here, we study grain growth with single-particle kinetics in colloidal polycrystals using video microscopy. Rich grain-growth phenomena are revealed in three shear regimes, including the normal grain growth (NGG) in weak shear melting-recrystallization process in strong shear. For intermediate shear, early stage NGG is arrested by built-up stress and eventually gives way to dynamic abnormal grain growth (DAGG). We find that DAGG occurs via a melting-recrystallization process, which naturally explains the puzzling stress drop at the onset of DAGG in metals. Moreover, we visualize that grain boundary (GB) migration is coupled with shear via disconnection gliding. The disconnection-gliding dynamics and the collective motions of ambient particles are resolved. We also observed that grain rotation can violate the conventional relation R x B = constant (R is the grain radius, and B is the misorientation angle between two grains) by emission and annihilation of dislocations across the grain, resulting in a step-by-step rotation. Besides grain growth, we discover a result in shear-induced melting: The melting volume fraction varies sinusoidally on the angle mismatch between the triangular lattice orientation of the grain and the shear direction. These discoveries hold potential to inform microstructure engineering of polycrystalline materials.