等原子比FeCrMnNi高熵合金的热变形行为

Hot Deformation Behavior of Equiatomic FeCrNiMn High Entropy Alloy

采用等温压缩实验,对FeCrNiMn等原子比高熵合金在900~1050℃和0.001~1 s^(−1)区间内的热变形行为进行了研究。结果表明,合金的初始组织主要由等轴面心立方晶粒和细小体心立方相颗粒构成。合金的流变曲线呈现典型的单峰形,随着温度的提高和应变速率的降低,峰值应力显著下降。基于双曲正弦方程建立了预测流变应力的本构模型,同时计算了合金的应力指数和表观变形激活能,分别为3.13和405 kJ/mol。基于动态材料模型建立了合金在不同应变量下的热加工图,发现所有热加工图中均未出现变形失稳区,说明合金具有优异的变形能力。通过与变形组织的对比发现,变形组织与能量耗散因子值密切相关。当能量耗散因子值为28%时,再结晶体积分数仅为17.6%;当能量耗散因子值为38%时,再结晶体积分数则提高至37.5%。通过热加工图确定了合金的2个最佳热变形参数区间:900~940℃/10^(−3)~10^(−1.3)s^(−1)和960~1050℃/10^(−3)~10^(−0.3)s^(−1)。

The hot deformation behavior of the equiatomic FeCrNiMn high entropy alloy was studied through the isothermal compression at 900~1050℃with strain rate of 0.001~1s^(−1).Results show that the initial microstructure is mainly composed of equiaxed grains with face-centered cubic structure and fine body-centered cubic phase particles.The flow curves exhibit the typical single stress peak type.The peak stress is decreased significantly with increasing the temperature and decreasing the strain rate.The constitutive model was developed based on the hyperbolic-sine law to predict the flow stress.The stress exponent and the apparent activation energy were calculated as 3.13 and 405 kJ/mol,respectively.The processing maps were obtained based on the dynamic material model at different strains.It is found that no instability zone appears in the processing maps at different strains,suggesting the excellent hot deformability of the alloy.The deformation microstructure is closely related to the power dissipation efficiencyη.The recrystallization fraction is 17.6vol%whenηis 28%,and it is increased to 37.5vol%whenηis 38%.Two optimal hot working condition ranges can be identified according to the processing maps:900~940℃/strain rate of 10^(−3)~10^(−1).3 s^(−1)and 960~1050℃/10^(−3)~10^(−0.3)s^(−1).