Tailoring phase transformation and precipitation features in a Al₂₁Co_19.5Fe_9.5Ni₅₀ eutectic high-entropy alloy to achieve different strength-ductility combinations

Eutectic high-entropy alloys (EHEAs) that combine the advantages of HEAs and eutectic alloys are promising materials for high-temperature environments. However, the mechanical properties of currently developed EHEAs still cannot meet the servicing requirements. Here, we propose a strategy to optimize the tensile properties in a Al₂₁Co_19.5Fe_9.5Ni₅₀ EHEA by regulating the phase transformation and precipitation features. The results showed that the as-cast Al₂₁Co_19.5Fe_9.5Ni₅₀ EHEA mainly consists of face-centered cubic (FCC) and B2 phases showing a lamellar morphology, and the FCC and B2 phases keep a stable K-S orientation relationship. Solution treatment at 900 and 1100 °C followed by furnace cooling to room temperature leads to a significant precipitation of L1₂ phases within the FCC phases. In the subsequent tensile deformation process, dispersed L1₂ phases and the transformation from B2 to L1₀ phases can significantly enhance the yield strength of the designed EHEA. Furthermore, solution treatment at the same temperature, followed by rapid water quenching, results in the appearance of numerous L1₀ phases within the B2 phases. The transformation from L1₀ to B2 phases during subsequent tensile deformation can make the B2 and FCC phases return to a K-S orientation relationship. This, in turn, reduces the tendency for dislocation pile-ups at the phase interfaces and improves the ductility. We believe that this work will provide some new references for designing EHEAs with excellent mechanical properties.