Superplastic deformation in metals and alloys, characterized by ultrahigh ductility (exceeding 300 %) without cracking at elevated temperatures, is a critical process for manufacturing complex-shaped components. While a few grain-boundary (GB)-mediated deformation mechanisms have been identified as essential contributors to superplasticity in fine-grained polycrystals (grain size is typically <10 μm), it is still a challenge to maintain a steady fine-grained microstructure and sustainable plastic flow at high temperatures. Partially due to the lack of a quantitative description of dislocation-GB reactions, it has not been well recognized how grain coarsening can be suppressed by the external loading during superplastic deformation. In this work, we address this challenge by formulating a disclination-dislocation coupling equation within the Lie-algebra framework, providing a quantitative understanding of the interactions between disclinations, dislocations, and GBs. Using quasi-in-situ electron backscattered diffraction (EBSD) analysis in Mg alloys, we systematically investigate the multiscale interactions of the defects and their impact on grain structure evolution. Three key mechanisms that suppress conventional grain coarsening have been identified, i.e., disclination-assisted GB accommodation, disclination-GB pinning, and disclination-induced sub-GB crossing, all of which are captured by the proposed equation. This study contributes to the broader field of plasticity by linking macroscopic deformation behavior with microscopic mechanisms, offering new insights into the theory of superplastic deformation in metals and alloys.

中文翻译：

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超塑性变形下镁合金倾斜介导的晶界结构演变


金属和合金的超塑性变形具有超高延展性（超过 300%），在高温下不会开裂，是制造复杂形状部件的关键工艺。虽然一些晶界 （GB） 介导的变形机制已被确定为细晶粒多晶（晶粒尺寸通常为 <10 μm）超塑性的重要因素，但在高温下保持稳定的细晶粒微观结构和可持续的塑性流动仍然是一个挑战。部分由于缺乏位错-GB 反应的定量描述，尚未很好地认识到在超塑性变形过程中如何通过外部载荷抑制晶粒粗化。在这项工作中，我们通过在李代数框架内建立离散-位错耦合方程来应对这一挑战，从而提供了对倾斜、位错和 GB 之间相互作用的定量理解。使用镁合金中的准原位电子背散射衍射 （EBSD） 分析，我们系统地研究了缺陷的多尺度相互作用及其对晶粒组织演变的影响。已经确定了抑制常规颗粒粗化的三种关键机制，即离散度辅助的 GB 调节、离散化-GB 固定和离散度诱导的亚 GB 交叉，所有这些都被所提出的方程捕获。本研究通过将宏观变形行为与微观机制联系起来，为更广泛的塑性领域做出了贡献，为金属和合金的超塑性变形理论提供了新的见解。