The distribution of geometrically necessary dislocation (GND) densities is critical to understanding the heterogeneous plastic deformation at intragranular scales in polycrystals. In this work, we performed an in situ electron backscatter diffraction (EBSD) measurement during the tensile test on a polycrystalline Al-Mg alloy. The EBSD patterns were processed through the integrated digital image correlation algorithm to enhance angular resolution. Based on the Nye dislocation density tensor, GND densities of 18 dislocation types in fcc crystals were resolved and mapped at macroscopic strains ranging from 5% to 16%. The evolution of GND distribution showed that GNDs were generated near grain boundaries at small strains and later localized at grain interiors along subgrain boundaries and slip bands at large strains. The inhomogeneous increase in GND densities of different dislocation types, representing dislocation substructures, along the subgrain boundaries was disclosed. Meanwhile, high GND densities were observed along the slip bands when a double noncoplanar slip system was activated inside the grains. The obstructed movement of dislocations by Lomer junctions explained the GND storage in different slip planes. The existence of Lomer junctions was proven by Burgers circuit analysis with high-resolution transmission electron microscopy, which explained the increase in screw dislocation density according to the dislocation reaction.

中文翻译：

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通过原位 EBSD 解决 Al-Mg 多晶中局部几何必要位错密度


几何必要位错（GND）密度的分布对于理解多晶晶内尺度的异质塑性变形至关重要。在这项工作中，我们在多晶铝镁合金的拉伸试验过程中进行了原位电子背散射衍射 (EBSD) 测量。 EBSD 图案通过集成数字图像相关算法进行处理，以增强角分辨率。基于 Nye 位错密度张量，在 5% 至 16% 的宏观应变范围内解析并绘制了 fcc 晶体中 18 种位错类型的 GND 密度。 GND 分布的演变表明，GND 在小应变时在晶界附近产生，随后在大应变时沿着亚晶界和滑移带定位在晶粒内部。揭示了代表位错亚结构的不同位错类型的 GND 密度沿亚晶界的不均匀增加。同时，当晶粒内部激活双非共面滑移系统时，沿滑移带观察到高 GND 密度。洛默结阻碍位错运动解释了不同滑移面中的 GND 存储。伯格斯电路分析和高分辨率透射电子显微镜证明了洛默结的存在，这解释了位错反应导致的螺旋位错密度的增加。