Tailoring phase transformation and precipitation features in a Al21Co19.5Fe9.5Ni50 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 Al21Co19.5Fe9.5Ni50 EHEA by regulating the phase transformation and precipitation features. The results showed that the as-cast Al21Co19.5Fe9.5Ni50 EHEA mainly consists of 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.