This study investigates two key aspects of the low cycle fatigue (LCF) behavior of alloys from the Cr-Mn-Fe-Co-Ni system at room temperature: (1) the influence of stacking fault energy (SFE) in single-phase face-centered cubic (FCC) alloys and (2) a grain size reduction triggered by the precipitation of a small amount of σ-phase. The first effect is investigated using model alloys (Cr26Mn20Fe20Co20Ni14 and Cr14Mn20Fe20Co20Ni26 in at.%, grain size: ∼60 µm), which have distinct SFEs at room temperature. A reduction in SFE from 69 to 23 mJ/m2 results in a 10 to 20 % increase in tensile/compressive peak stresses, i.e., cyclic strength, across all examined strain amplitudes (±0.3 %, ±0.5 %, and ±0.7 %) while maintaining comparable fatigue lives. Despite its higher cyclic strength, the low-SFE alloy exhibits delayed, and less evolved dislocation substructures than the other alloy. In both single-phase alloys, fatigue cracks originated from the surface reliefs, surface-exposed coherent annealing twin boundaries, and occasionally from high-angle grain boundaries. However, the crack propagation rate was slower in the low-SFE alloy, contributing to its superior fatigue resistance. By aging the low-SFE Cr26Mn20Fe20Co20Ni14 alloy differently, we could induce the precipitation of ∼5 % σ-phase during recrystallization, which strongly reduced the FCC grain size to ∼5 µm. With this microstructure, the cyclic strength increased by 50–65 % and remained more stable during fatigue testing while maintaining a comparable life. The σ-precipitates were found to deflect and arrest fatigue cracks, while extensive deformation twinning around cracks complements slip activity and reduces crack propagation rate. Overall, the σ-phase-assisted grain size reduction is 3 to 5 times more effective in improving cyclic strength than SFE reduction.

中文翻译：

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通过改变堆叠故障能和σ （σ）相辅助晶粒尺寸减小来提高Cr-Mn-Fe-Co-Ni多主元素合金的抗疲劳性能


本研究研究了 Cr-Mn-Fe-Co-Ni 系统合金在室温下低周疲劳 （LCF） 行为的两个关键方面：（1） 单相面心立方 （FCC） 合金中堆叠故障能 （SFE） 的影响，以及 （2） 少量 σ 相析出引发的晶粒尺寸减小。使用模型合金（Cr26Mn20Fe20Co20Ni14 和 Cr14Mn20Fe20Co20Ni26，at.%，晶粒尺寸：∼60 μm）研究了第一个影响，它们在室温下具有不同的 SFE。SFE 从 69 mJ/m2 降低到 23 mJ/m2 导致所有检查的应变幅值（±0.3 %、±0.5 % 和 ±0.7 %）的拉伸/压缩峰值应力（即循环强度）增加 10% 到 20%，同时保持相当的疲劳寿命。尽管具有更高的循环强度，但与其他合金相比，低 SFE 合金表现出延迟且演化程度较低的位错子结构。在这两种单相合金中，疲劳裂纹都源于表面起伏、表面暴露的相干退火双晶界，偶尔也来自大角度晶界。然而，低 SFE 合金的裂纹扩展速率较慢，这有助于其卓越的抗疲劳性。通过对低SFE Cr26Mn20Fe20Co20Ni14合金进行不同的时效处理，我们可以在再结晶过程中诱导∼5 %的σ相沉淀，从而将FCC晶粒尺寸强烈减小到∼5 μm。利用这种微观结构，循环强度提高了 50-65%，并且在疲劳测试期间保持更稳定，同时保持了相当的使用寿命。发现σ析出物可以偏转和阻止疲劳裂纹，而裂纹周围的广泛变形孪晶补充了滑移活动并降低了裂纹扩展速率。 总体而言，σ相辅助晶粒尺寸减小在提高循环强度方面的有效性是 SFE 减小的 3 到 5 倍。