In this paper, a physical-based constitutive model for cryogenic deformation was established by introducing internal variables related to temperature, T and grain size, d. Uniaxial tensile tests and microstructure observations were carried out to reveal macroscopic deformation behavior and corresponding microscopic deformation mechanism. The classical Kocks–Mecking model was modified by distinguishing the significant differences in the dislocation evolution in the grain interior and in the vicinity of the grain boundary. The parameters of the constitutive model were optimized by genetic algorithm (GA). The developed constitutive model was comprehensively validated, including the stress-strain curves and formability indexes at the macro level and the evolution of dislocation density at the micro level by using in-situ digital image correlation (DIC) tests and quasi-in-situ electron backscattered diffraction (EBSD) characterization. The coupling effects of grain size and cryogenic temperature (CT) on the evolution of dislocation are quantitatively analyzed and discussed based on the established constitutive model. The studies show that the constitutive model can effectively address the coupling effects of grain size and CT on the deformation behavior of pure aluminum, and accurately describe the deformation characteristics of heterogeneous sheets with gradient grain size at different temperatures. In addition, parametric analysis shows that the predominant dislocation annihilation in ultra-fine grained (UFG) pure aluminum gradually transitions from the vicinity of the grain boundary to the grain interior with the decrease in temperature, resulting in the significant weakening of the strength-plasticity trade-off relationship at cryogenic temperature. These results deepen the understanding of the grain size-dependent cryo-deformation and inspire a promising idea for the direct manufacture of heterogeneous components with grain size gradients.

中文翻译：

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基于晶粒尺寸依赖性位错演化的低温变形建模


在本文中，通过引入与温度 T 和晶粒尺寸 d 相关的内部变量，建立了基于物理的低温变形本构模型。进行了单轴拉伸试验和微观结构观察，以揭示宏观变形行为和相应的微观变形机制。通过区分晶粒内部和晶界附近位错演变的显著差异，对经典的 Kocks-Mecking 模型进行了修改。通过遗传算法 （GA） 对本构模型参数进行优化。利用原位数字图像相关 （DIC） 测试和准原位电子背散射衍射 （EBSD） 表征，对所开发的本构模型进行了全面验证，包括宏观层面的应力-应变曲线和成形性指标，以及微观层面位错密度的演变。基于建立的本构模型，定量分析和讨论了晶粒尺寸和低温 （CT） 对位错演变的耦合效应。研究表明，本构模型可以有效解决晶粒尺寸和CT对纯铝变形行为的耦合效应，准确描述不同温度下梯度晶粒尺寸非均质片材的变形特性。此外，参数分析表明，随着温度的降低，超细晶粒 （UFG） 纯铝中占主导地位的位错湮没逐渐从晶界附近过渡到晶粒内部，导致低温下强度-塑性权衡关系显著减弱。 这些结果加深了对晶粒尺寸依赖性低温变形的理解，并为直接制造具有晶粒尺寸梯度的异质部件激发了有前途的想法。