Face-centered cubic (FCC) medium entropy alloys (MEAs) have received considerable attention due to their impressive mechanical properties and responses. However, their practical application is limited by their modest yield strengths. The potential enhancement of the mechanical properties of single-phase MEAs was explored in this study through a synergistic approach combining heterogeneous structure design with subsequent cryo-pre-straining. A heterogeneous lamella structure was produced in a single-phase Fe55Mn20Cr15Ni10 MEA via two-step rolling and annealing. Cryo-pre-straining at varying degrees (6, 12, 21, and 36%) introduced hexagonal close-packed (HCP) phase, high-density dislocations, twins, and stacking faults, leveraging the reduced stacking fault energy at cryogenic temperatures. This process enhanced the alloy's yield strength from 353 MPa to 1.2 GPa (compared to the baseline uniform coarse-grained structure), while maintaining an acceptable total elongation of 8.4%. The impact of cryo-pre-straining on the microstructure and mechanical properties of the MEA was assessed using in-situ synchrotron X-ray diffraction analysis. Cryo-pre-straining (36%) achieved a higher dislocation density (6.1 × 1015m−2) compared to room-temperature straining (2.5 × 1015m−2). The stress contribution from HCP-martensite and the evolution of dislocation density during loading were quantified, along with observations of negative stacking fault probability and strain-induced HCP→FCC reverse transformation in cryo-pre-strained samples under loading conditions. Furthermore, the contributions of regulated microstructures to the enhancement of yield strength were quantitatively assessed.

中文翻译：

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异质结构设计与低温预应变协同强化的亚稳态中等熵合金的变形机理


面心立方 （FCC） 中等熵合金 （MEA） 因其令人印象深刻的机械性能和响应而受到广泛关注。然而，它们的实际应用受到其适度的屈服强度的限制。本研究通过结合异质结构设计与随后的冷冻预应变的协同方法，探索了单相 MEA 机械性能的潜在增强。在单相 Fe55Mn20Cr15Ni10 MEA 中通过两步轧制和退火制备了异质薄片结构。不同程度（6、12、21 和 36%）的冷冻预应变引入了六边形密堆积 （HCP） 相、高密度位错、孪晶和堆叠故障，利用低温下降低的堆叠故障能量。该工艺将合金的屈服强度从 353 MPa 提高到 1.2 GPa（与基线均匀粗晶结构相比），同时保持可接受的 8.4% 总伸长率。使用原位同步加速器 X 射线衍射分析评估了冷冻预应变对 MEA 微观结构和机械性能的影响。与室温应变 （2.5 × 1015m-2） 相比，冷冻预应变 （36%） 实现了更高的位错密度 （6.1 × 1015m-2）。量化了 HCP-马氏体的应力贡献和加载过程中位错密度的演变，以及在加载条件下低温预应变样品中负堆叠故障概率和应变诱导的 HCP→FCC 反向转变的观察。此外，定量评估了调节的微观结构对提高屈服强度的贡献。