Subgrain boundary-driven spheroidization synergistically enhances strength and ductility in Ni-based eutectic medium-entropy alloys

Eutectic high-entropy alloys (EHEAs) are extensively studied for their exceptional mechanical properties; however, the dependence of traditional EHEAs on Co restricts their industrial applications. In this study, a novel Co-free Ni₅₅Fe₂₈Al₁₇ (at%) EHEA was developed. High-temperature heat treatment induced defect-driven interface reconstruction, resulting in dense internal boundaries within the lamellar BCC_B2 structures. This process created curvature variations and concentrated stress, prompting localized separation and reformation that transformed the lamellae into lower-energy spherical morphologies. This spheroidization simultaneously reduced interfacial stress accumulation and controls dislocation motion, mitigating phase deformation mismatch. A 12 h treatment significantly enhanced the mechanical properties, achieving a strength of 1017.42 MPa and ductility of 21.16 %. These values approach those of the high-performance AlCoCrFeNi_2.1 EHEA (1061 MPa, 24.8 %) under comparable treatment, representing increases of 129.74 % in strength and 484.21 % in ductility compared to the untreated state. This strategy provides a theoretical framework for the development of high-strength and ductile alloys.