Fe40Mn20Cr20Ni20高熵合金在低温下的动态拉伸变形机制

Dynamic tensile deformation mechanisms of Fe40Mn20Cr20Ni20 high-entropy alloys at cryogenic temperatures

摘要:

高熵合金（HEAs）作为一种新兴的结构材料，在高应变速率、高温或低温方面具有很大的应用潜力。先前的研究主要是高熵合金在高速加载或低温下的力学行为，仅限于单一的极端环境。本文主要讨论了Fe40Mn20Cr20Ni20高熵合金在高温或低温以及高应变速率下(霍普金森杆)的力学行为和微观机制，并使用相关理论模型对合金的屈服强度和流变应力进行拟合。拉伸试验结果表明，在降低温度或提高应变速率的条件下，该高熵合金都表现出优异的强度-塑性协同作用和优异的加工硬化能力。在动态拉伸过程中，不同形态的位错和变形孪晶的相互作用共同提高了高熵合金的强度和加工硬化能力。使用Zerilli-Armstrong（Z-A）本构模型预测了高熵合金屈服强度的温度敏感性和应变率敏感性。同时，使用泰勒模型预测了动态拉伸下高熵合金流变应力随应变速率的变化情况，并将该模型应用到低温动态下，拟合结果与实验结果基本一致，为后续进行高熵合金强度的预测提供理论基础。

Abstract:

As an emerging structural material, high-entropy alloys (HEAs) have significant application potential in high-strain-rate environments and across a range of temperatures, including both high and low temperatures. Previous studies mainly focused on the mechanical behavior of HEAs under high-speed loading or low temperature, which is limited to a single extreme environment. This paper primarily discusses the mechanical behavior and microscopic mechanism of the Fe40Mn20Cr20Ni20 high-entropy alloy (HEA) at high and low temperatures and high strain rates (Split Hopkinson bar) and utilizes relevant theoretical models to fit the yield strength and flow stress of the HEA. The tensile test results show that the HEA exhibits excellent strength-plastic synergy and excellent work-hardening ability under the condition of reducing temperature or increasing strain rates. During the dynamic tensile process, the interaction of different forms of dislocations and deformation twins together improves the strength and work-hardening ability of the HEA. The Zerilli-Armstrong (Z-A) constitutive model was used to predict the temperature sensitivity and strain-rate sensitivity of the yield strength of the HEA. At the same time, the Taylor model was used to predict the change of the HEA flow stress with the strain rate under dynamic tension, and the model was applied to low-temperature dynamics. The fitting results were consistent with the experimental results, which provided a theoretical basis for the subsequent prediction of HEAs strengths.