The evolution of eutectic microstructure and mechanical properties of AlxCoCrFeNi2.1 high-entropy alloys

In order to reveal the evolution of microstructure and properties of AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) near the eutectic composition, a series of AlxCoCrFeNi2.1 high-entropy alloys (HEAs) were prepared and their microstructure, phase composition and mechanical properties were systematically characterized. Results show that with the increase of Al content, the crystal structure of AlxCoCrFeNi2.1 alloys change progressively from single FCC to BCC/B2 structure, and the microstructure evolution experience dendritic structure, hypoeutectic structure, "steel frame"-like eutectic structure, "coral"-like pseudoeutectic structure, hypereutectic structure, equiaxed structure, leading to the corresponding changes in mechanical properties. Moreover, we detected a novel "coral"-like pseudoeutectic structure that consists of BCC/B2 and FCC phases with volume ratio close to 1:1 in Al1.1CoCrFeNi2.1 alloy. This pseudoeutectic structure brings both higher elongation and strength than that of AlCoCrFeNi(2.1)EHEA. Above findings will further advance the engineering application of AlCoCrFeNi2.1 EHEA system.