Construction of multiscale secondary phase in Al0.25FeCoNiV high-entropy alloy and in-situ EBSD investigation

Developing high-entropy alloys (HEAs) faces challenges owing to the inherent strength-ductility trade-off. This study systematically investigated the microstructure and mechanical properties of Al0.25FeCoNiV face-centered cubic (FCC) and body-centered cubic (BCC) duplex HEA, subjected to 70% cold rolling and annealing at various temperatures. The mechanism of the nonlinear effect of the annealing temperature on precipitation in duplex HEA was investigated. An economical and efficient thermo-mechanical processing route was developed to construct a multiscale BCC secondary phase. After 70% cold rolling and annealing at 1373 K, the yield strength (YS), ultimate tensile strength, and fracture elongation were 750 MPa, 1169 MPa, and 46.5%, respectively. This demonstrates superior strength-ductility coordination. In-situ electron backscatter diffraction (EBSD) tensile experiments were performed using a self-designed device to observe the dynamic evolution of the grain orientation and grain boundary distribution under diverse strain conditions. The influence of the multiscale BCC secondary phase on the mechanical properties was comprehensively investigated. The findings suggested that the exceptional mechanical performance was attributed to the coupled mechanism of multistage hetero-deformation-induced (HDI) strengthening and strain hardening produced by the multiscale BCC phase. Quantitative calculations revealed that the HDI strengthening (420 MPa) contributed over 50% to YS. This study lays a solid theoretical foundation for optimizing process parameters and innovating high-performance HEAs for engineering applications.