Deformable Eutectic Alloy With Near‐Theoretical Yield Strength via Hierarchical Nanoscale Multiphases and Sessile Defects

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, L1₂ and D0₂₂ 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 L1₂ precipitates, sessile planar faults, and misfit-interface dislocations, while hard-Laves nanolamellae are toughened by deformable D0₂₂ 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.