In the present study, a systematic investigation on the effect of Fe content on the Hall-Petch coefficient of (CoCrMnNi)_100-x Fe_x (x = 20, 40, 50, and 60) medium- and high-entropy alloys (M/HEAs) was carried out. The cold-rolled alloys were annealed at 900 °C and 1000 °C between 3 min and 10 h for recrystallization. Scanning electron microscope with a backscattered detector was used to obtain micrographs of recrystallized specimens for grain size calculation. Tensile testing was used to evaluate the mechanical properties of the alloys. The microstructure showed that regardless of the alloy composition, the grain size was approximately similar when subjected to the same heat treatment condition. Moreover, all the alloys obeyed the classical Hall-Petch relationship. Friction stress (solid solution, SS strengthening) decreased with an increase of Fe content, which was attributed to weak lattice distortion caused by the reduction of the atomic size misfit. The Hall-Petch coefficient, which represents grain boundary (GB) strengthening, also decreases as the Fe content increases. A linear relationship between intrinsic stacking fault energy and Hall-Petch coefficient was found not to exist. However, it is proposed that the monotonic decrease of the Hall-Petch coefficient is directly related to the unstable stacking fault energy (γ_USFE). As a result, an increase of Fe content in (CoCrMnNi)_100-x Fe_x alloy system leads to an increase of γ_USFE, which in turn weakens GB strengthening (Hall-Petch coefficient). Moreover, HEAs and MEAs with higher Fe content tend to have low yield strength due to weak contributions from both SS and GB strengthening. Therefore, to design superior MEAs and HEAs with enhanced strength, the choice of principal elements and their respective contents is imperative for an optimized contribution from both SS and GB strengthening mechanisms.

在本研究中，系统研究Fe含量对（CoCrMnNi）_{100- x} Fe _x的霍尔-Petch系数的影响（x = 20、40、50和60）进行了中熵和高熵合金（M / HEAs）的研究。将冷轧合金在3分钟至10小时之间于900°C和1000°C进行退火以进行重结晶。使用带有反向散射检测器的扫描电子显微镜获得重结晶试样的显微照片，以进行晶粒尺寸计算。拉伸测试用于评估合金的机械性能。显微组织表明，在相同的热处理条件下，无论合金成分如何，晶​​粒尺寸都近似相似。而且，所有合金都遵循经典的霍尔-皮奇关系。随着Fe含量的增加，摩擦应力（固溶，SS强化）降低，这归因于由于原子尺寸失配的减少而导致的弱晶格畸变。随着Fe含量的增加，代表晶界（GB）增强的Hall-Petch系数也随之降低。发现本征叠层故障能量与霍尔-Petch系数之间不存在线性关系。然而，有人提出霍尔-Petch系数的单调下降与不稳定的堆垛层错能（γ_USFE）。结果，（CoCrMnNi）_{100- x} Fe _x合金体系中铁含量的增加导致_γUSFE的增加，进而削弱了GB的增强（霍尔-普奇系数）。此外，由于SS和GB强化的贡献较弱，Fe含量较高的HEA和MEA往往具有较低的屈服强度。因此，要设计具有增强强度的高级MEA和HEA，必须选择主要元素及其各自的含量，以实现SS和GB增强机制的最佳贡献。