Micromechanical Behaviors of Fe20Co30Cr25Ni25 High Entropy Alloys with Partially and Completely Recrystallized Microstructures Investigated by In-Situ High-Energy X-ray Diffraction

This work conducts a processing strategy to obtain the partially and completely recrystallized microstructures by cold rolling and annealing at different temperatures for a near-equiatomic Fe₂₀Co₃₀Cr₂₅Ni₂₅ high entropy alloy (HEA). The in-situ synchrotron-based high-energy–X-ray diffraction (HE-XRD) technique was adopted to investigate the mechanical behaviors and microstructural evolution of Fe₂₀Co₃₀Cr₂₅Ni₂₅ HEAs with heterogeneous (partially recrystallized) and homogeneous (completely recrystallized) microstructures during tensile deformation. The heterogeneous and homogeneous microstructures were obtained by annealing for 1 hour at 600 °C and 650 °C, respectively (hereinafter 600 and 650 A, respectively). No obvious phase transformation was found during the tensile deformation. The partially recrystallized HEA has a higher initial dislocation density (2.30 × 10¹⁵ m⁻²) than that in the completely recrystallized HEA (9.57 × 10¹⁴ m⁻²). The grains orientated with [200] parallel to the loading direction (LD) yield before the macroyielding (under ~ 951 MPa) in 600 A with the incomplete recrystallized microstructures. The results of transmission electron microscopy (TEM) and HE-XRD confirm that the deformation in the partially recrystallized microstructures mainly relies on dislocation slip, leading to a small number of deformation twins and very high-density dislocations at fracture, while a large number of deformation twins occurred in the completely recrystallized structures during deformation, leading to the obvious strain hardening.