ABSTRACT Eutectic high‐entropy alloys (EHEAs), a typical bioinspired lamellar composite, have the potential to achieve high strength and good ductility simultaneously for structural applications through microstructure modification. However, an extreme modulus/hardness mismatch between constituent phases leads to premature fracture and severely limits the achievable yield strength by impeding plasticity at room temperature. Here, a CoCrFeNiTa 0.4 EHEA designed via suction casting followed by precise thermal treatment, which exhibits sessile interface defects and hierarchical nano‐multiphase structures consisting of FCC‐Laves eutectic lamellae, L1 2 and D0 22 coprecipitates, attains a near‐theoretical yield strength of 2.6 GPa alongside sufficient plasticity of 13.6%. This breakthrough is attributed to multiple mechanisms, characterizing soft‐FCC nanolamellae strengthened by coherent L1 2 precipitates, sessile planar faults, and misfit‐interface dislocations, while hard‐Laves nanolamellae are toughened by deformable D0 22 precipitates. All of these factors lead to the reduced modulus/hardness mismatch between FCC and Laves lamellae. The results indicate that the long‐range modulus/hardness‐matching and short‐range heterostructure, via hierarchical multiple phases and defects, are pivotal for next‐generation dual‐ and multi‐phase alloys to achieve theoretical strength while retaining impressive plasticity.
Luo et al. (Mon,) studied this question.
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