Dual heterostructures via partial recrystallization: Synergistic enhancement of strength-ductility in Al₁₆Co₁₁Cr₁₅Fe₂₅Ni₃₃ FCC/BCC eutectic high-entropy alloy

Eutectic high-entropy alloys (EHEAs) have attracted significant attention owing to their balanced strength-ductility performance and excellent castability. In this study, two distinct heterogeneous microstructures, i.e., lamellar heterostructures and grain size heterostructures, were engineered in the Al₁₆Co₁₁Cr₁₅Fe₂₅Ni₃₃ dual-phase (face-centered cubic, FCC/body-centered cubic, BCC) eutectic high-entropy alloy through a controlled thermomechanical process. This process involved four cycles of cold rolling (each achieving 20 % thickness reduction, resulting in a total deformation of 80 %), followed by partial recrystallization annealing at 750°C for 20 min and subsequent water quenching. This processing route not only preserved the intrinsic lamellar eutectic morphology but also induced in-situ nanoscale precipitates (BCC precipitates within the FCC matrix and FCC precipitates within the BCC matrix) in the lamellar regions. The synergistic effect of the dual heterostructures and in-situ precipitates generated a strong back stress strengthening effect, enabling simultaneous improvements in both strength and ductility. Compared with the as-cast alloy (yield strength: 520 MPa, ultimate tensile strength: 967 MPa, total elongation: 20.2 %), the partially recrystallized Al₁₆Co₁₁Cr₁₅Fe₂₅Ni₃₃ alloy exhibited superior mechanical properties: yield strength of 1104 MPa, an ultimate tensile strength of 1404 MPa, and a total elongation of 25.8 %. These superior mechanical properties highlight the potential of the proposed partial recrystallization strategy for advancing EHEA development, offering a novel approach to enhance the performance of eutectic alloy and expands the EHEA-based design toolkit for high-performance materials.