The study of alloys exhibiting noteworthy strength-ductility synergy at ambient and cryogenic temperatures has been a persistent area of interest in materials engineering. This interest extends to the recent development of high-entropy alloys (HEAs). The current investigation delves into the impact of diverse thermo-mechanical treatments on the phase and microstructure evolution in a face-centered cubic (FCC) AlCoFeNiCr HEA. The transition from solid-solution annealing to recrystallization annealing leads to the formation of the desired hierarchical B2+L1+ precipitates, accompanied by a heterogeneous FCC matrix. The initiation of the B2 phase originates from nucleation on defect-rich sites, such as deformation bands. However, the coherent L1 phase homogeneously forms in the FCC matrix at intermediate temperature aging, as these sites are scarce or occupied. A heterogeneous structure emerges from the transition in annealing temperatures and the pinning effect of the B2 precipitates. The resulting heterogeneous structure exhibits an exceptional strength-ductility synergy at both room and liquid nitrogen (LN) temperatures. This is evident in its mechanical properties with a yield strength of ∼717 MPa / ∼1109 MPa, an ultimate tensile strength of ∼1086 MPa / ∼1609 MPa, and an elongation of ∼34.3 % / ∼43.2 % at room / LN temperatures. The formation of deformation twins (DTs) is facilitated by localized stress buildup from hetero-deformation-induced (HDI) hardening stress at room temperature. The exceptional strength and ductility at LN temperature are attributed to a combination of factors. These include a high-density of stacking faults (SFs), DTs, and their interactions, including those with precipitates, SFs-based substructures, and Lomer-Cottrell locks. These multiple deformation mechanisms ensure consistent and sustained strain-hardening even under substantial strain. This paper sheds light on the complex interplay of microstructure, deformation mechanisms, and mechanical properties in the AlCoFeNiCr HEA, potentially guiding the development of ultra-strong yet ductile alloys for cryogenic applications.

中文翻译：

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具有分级沉淀异质结构的 Al7.5Co20.5Fe24Ni24Cr24 高熵合金在室温和液氮温度下具有出色的强度-延展性协同作用

对在环境温度和低温下表现出显着的强度-延展性协同作用的合金的研究一直是材料工程领域持续关注的领域。这种兴趣延伸到了高熵合金（HEA）的最新发展。目前的研究深入探讨了不同的热机械处理对面心立方 (FCC) AlCoFeNiCr HEA 中相和微观结构演变的影响。从固溶退火到再结晶退火的转变导致形成所需的分级 B2+L1+ 沉淀物，并伴有异质 FCC 基质。 B2 相的起始源于缺陷丰富的位点（例如变形带）上的成核。然而，在中温老化时，相干 L1 相在 FCC 基体中均匀形成，因为这些位点稀缺或被占据。退火温度的转变和 B2 沉淀物的钉扎效应产生了异质结构。由此产生的异质结构在室温和液氮 (LN) 温度下均表现出卓越的强度-延展性协同作用。这在室温/液氮温度下其屈服强度为 ∼717 MPa / ∼1109 MPa、极限拉伸强度为 ∼1086 MPa / ∼1609 MPa 以及伸长率为 ∼34.3 % / ∼43.2 % 的机械性能中得到体现。室温下异质变形诱发 (HDI) 硬化应力的局部应力累积促进了形变孪晶 (DT) 的形成。液氮温度下优异的强度和延展性归因于多种因素的综合作用。其中包括高密度的堆垛层错 (SF)、DT 及其相互作用，包括那些具有沉淀物、基于 SF 的子结构和 Lomer-Cottrell 锁的相互作用。这些多重变形机制即使在巨大的应变下也能确保一致和持续的应变硬化。本文揭示了 AlCoFeNiCr HEA 中微观结构、变形机制和机械性能之间复杂的相互作用，有可能指导用于低温应用的超强延展合金的开发。