Novel Ni-Co-Cr-Al eutectic high-entropy superalloys with superb mechanical properties

Eutectic high-entropy alloys (EHEAs) with superior castability and mechanical properties are attractive for hightemperature applications. In this work, the novel Ni70-xCo10Cr20Alx eutectic high-entropy superalloys (EHESs) that have attained a 13 % reduction in density compared to the conventional superalloys, with the outstanding balance between mechanical properties and density were reported. These EHESs possess a lamellar heterogeneous structure consisting of face-centered cubic (FCC) and ordered body-centered cubic (B2) phases with L12 and BCC nano-precipitates, respectively. Moreover, the EHESs exhibit superb tensile properties at ambient and high temperatures, e.g. Ni52Co10Cr20Al18 alloy exhibited a yield and ultimate tensile strength and elongation of 787 MPa, 1133 MPa and 7.0 % respectively at ambient temperature; a yield and ultimate tensile strength of 563 MPa and 618 MPa at 750 degree celsius, which is even higher than those of the reported EHESs and traditional nickel-based superalloys at 700 degree celsius. It is revealed that the excellent combination of strength and plasticity originated from the synergic effects of the solid solution strengthening of Al, back stress hardening of finer eutectic lamellar structure, and precipitation strengthening of high-density nano-precipitates. Besides, deformation twins, superlattice stacking faults, and the anti-phase boundaries in the FCC(L12) phase further improved high-temperature strength and strain-hardening ability.