考虑加工硬化和动态软化的FeCrNiMn中熵合金本构模型

采用等温压缩分析了Fe_0.25Cr_0.25Ni_0.25Mn_0.25中熵合金在900~1050 ℃、0.001~1 s^-1应变速率范围内的流变行为。结果表明，热变形以动态再结晶为主，与其他低堆垛层错能的合金一样，流变曲线呈单峰形状。建立了本构模型来描述整个变形过程，分析了加工硬化行为和动态软化过程。利用Kocks-Mecking图发现，在加工硬化阶段，合金的硬化速率随应力呈线性降低，因此应力-应变行为可以用传统的位错密度模型来描述。同时，采用经典的JMAK方程描述由动态再结晶引起的软化过程。此外，对本构模型进行了进一步的修改，减少了参数的数量，简化了回归分析。所提出的半物理模型不仅可以准确地预测应变范围外的应力-应变行为，而且可用于其他低层错能合金。

A Simple Constitutive Model for FeCrNiMn Medium Entropy Alloy Considering Work-Hardening and Dynamic Softening

The flow behavior of a medium entropy alloy with a nominal composition of Fe_0.25Cr_0.25Ni_0.25Mn_0.25 was analyzed by isothermal compression performed in the temperature range of 900~1050 °C and strain rate range of 1~0.001 s^-1. The results show that the hot deformation is predominated by dynamic recrystallization, so that the flow curves exhibit a single-peak shape as those of other alloys with low stacking-fault energy. Particular emphasis was paid to develop a simple constitutive model which can describe the entire deformation history. For this purpose, the work-hardening behavior as well as the dynamic softening regime were analyzed. With the aid of Kocks-Mecking plots, it is found that the hardening rate of the present alloy is linearly decreased with stress in the work-hardening stage, and hence the stress-strain behavior can be described by the conventional dislocation density-based model. Meanwhile, the softening regime, which is caused by dynamic recrystallization, can be modelled by the classic JMAK equation. Besides, the model is further modified to reduce the number of parameters and simplify the regression analysis. The proposed semi-physical based model can not only accurately predict the stress-strain behavior to strain levels outside the experimental strain range, but can also be promoted to other alloys with low stacking-fault energy.