In order to investigate the effect of grain size on the fatigue limit of single-phase equiatomic high-entropy alloys (HEAs); CrMnFeCoNi, fabricated by spark plasma sintering, four-point bending fatigue tests were conducted at stress ratio of 0.1 under ambient condition. The surfaces of fatigued specimen were observed by in-situ optical microscopy, and fatigue crack initiation and propagation behaviors were analyzed by electron backscatter diffraction to elucidate the fatigue fracture mechanism in CrMnFeCoNi alloy with different grain sizes. The grain size of CrMnFeCoNi sintered compacts decreased with decreasing particle size of CrMnFeCoNi powders, and their fatigue limits tended to increase with decreasing grain size due to the Hall-Petch effect. Furthermore, fatigue cracks in the coarse-grained CrMnFeCoNi sintered compact were initiated at the boundary of annealing twins, whereas annealing twin boundaries were not observed near the crack initiation site of the fine-grained one. The fraction of twin boundaries in CrMnFeCoNi alloy tended to decrease with decreasing grain size; therefore, the grain refinement is an effective approach for increasing the fatigue limit of CrMnFeCoNi alloy because of both the Hall-Petch effect and the increase in the fatigue crack initiation resistance.

为了研究晶粒尺寸对单相等原子高熵合金（HEA）疲劳极限的影响；CrMnFeCoNi，通过放电等离子烧结制造，在环境条件下以0.1的应力比进行四点弯曲疲劳试验。通过原位光学显微镜观察疲劳试样表面，通过电子背散射衍射分析疲劳裂纹的萌生和扩展行为，阐明不同晶粒尺寸CrMnFeCoNi合金的疲劳断裂机理。CrMnFeCoNi烧结体的晶粒尺寸随着CrMnFeCoNi粉末粒径的减小而减小，并且由于Hall-Petch效应，它们的疲劳极限随着晶粒尺寸的减小而增加。此外，粗晶CrMnFeCoNi烧结体的疲劳裂纹起始于退火孪晶的边界，而在细晶裂纹起始位置附近未观察到退火孪晶边界。CrMnFeCoNi合金中孪晶界的比例随着晶粒尺寸的减小而减小；因此，晶粒细化是提高 CrMnFeCoNi 合金疲劳极限的有效途径，因为霍尔-佩奇效应和抗疲劳裂纹萌生能力的增加。