Unraveling microstructural evolution and mechanical properties of as-annealed CoFeNiMnVx (x=0.25, 0.5, 0.75, 1) high-entropy alloys

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This study investigates the microstructural evolution and mechanical properties of CoFeNiMnV x HEAs (x = 0.25, 0.5, 0.75, 1.0) after cold rolling and annealing, focusing on the interplay among V content, σ-phase precipitation, and recrystallization behavior. Thermodynamic calculations and experimental analyses, including XRD, SEM, EBSD, and TEM, were employed to characterize phase formation and microstructural transitions. The results reveal that increasing V content promotes σ-phase precipitation, which enhances strength but reduces ductility. Among the investigated alloys, the V0.75 alloy exhibited an optimal combination of strength and ductility (UTS = 955 ± 88 MPa,ɛ p = 22 ± 10 %), attributed to a partially recrystallized microstructure with controlled σ-phase formation. Quantitative analysis of the strengthening mechanisms indicates that non-recrystallized grain strengthening dominates at higher V contents, while solid-solution and precipitation hardening contribute synergistically. Overall, this work highlights the potential of V-modified CoFeNiMn-based HEAs as promising structural materials, achieving a superior balance of strength and ductility through tailored microstructural design.