On the microstructure and mechanical properties of the AlCoCrCuNi high entropy alloy processed in the semi-solid state

After semi-solid processing the thixo-cast microstructure consisted of a unique composition of globular grains with a B2-ordered body centered cubic structure (BCC) within coherent nano-cuboidal precipitations (average size of 60 nm). The grains contained near equiatomic concentrations of Al, Co, Cr and Ni. They were surrounded by a Cu-enriched homogeneously distributed solid solution with an L12-ordered structure and Co-Cr nano-precipitations. The complex microstructure was responsible for the high strength and moderate ductility at room temperature, which was confirmed by compression test results. The thixo-cast revealed a yield strength of 1580 MPa, while its compression strength at 6% of strain reached 2070 MPa at an average hardness of 581 HV. The obtained values of yield strength and hardness were about 20% higher than those of the ingot material after direct casting. The melting behavior, microstructure and mechanical properties obtained make the AlCoCrCuNi HEA a promising material for thixoforming.