Hot deformation characteristics and microstructure evolution of Al20Co36Cr4Fe4Ni36 eutectic high entropy alloy

Eutectic high entropy alloys (EHEAs) have garnered much research attention due to their excellent mechanical properties, superior castability, good oxidation resistance, and stable microstructure in a wide range of temperatures. Inspires from mature Ni and Co-based superalloys, a novel Al20Co36Cr4Fe4Ni36 EHEA was designed and prepared to obtain good mechanical properties at both room temperature and high temperatures in this study. The novel EHEA consists of a L12 phase and a B2 phase with a superior ultra-tensile strength of 1005 ± 40 MPa and a ductility of 8.8 ± 0.4% at room temperature. The engineering compressive stress–strain curves at 1073 K indicated that the current EHEA performs a high strength of 321 ± 9 MPa without fracture even at a high temperature of ~0.6 TE, which is even superior to some refractory high entropy alloys (RHEAs). The hot deformation behavior and microstructure evolution of the new EHEA was investigated at the temperature range of 1073 K to 1273 K and various strain rates from 10−3 s−1 to 10−1 s−1. The constitutive equation that describes the correlations between the flow stress, strain rate, and temperatures was constructed. Continuous dynamic recrystallization (CDRX) was the primary dynamic recrystallization (DRX) mechanism in both the L12 and B2 phases during hot deformation. However, the proportion of dynamic recrystallization grains in the L12 phase is higher than that in the B2 phase according to the high angle grain boundaries (HAGBs) under the same deformation condition, suggesting that the CDRX kinetics was faster and stronger in the L12 phase. The present study provided a new thought for designing EHEAs and an insight into the hot deformation behavior of EHEAs with lamellar morphologies.