Effect of Al contents on microstructure and mechanical properties of Al CoCrFeNiMo0.3 high-entropy alloys

Herein, Al x CoCrFeNiMo 0.3 ( x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) series alloys were fabricated with high-vacuum arc melting technique. The effect of Al contents on the microstructure and mechanical properties of the alloys was investigated. Results show that the phase structures of the alloys evolved from FCC + σ to FCC+ σ +B2 as Al content varies. The dendritic structure of the alloys undergoes refinement, with the most significant refinement observed at x = 0.2. At x = 0.5, the dendritic structure disappeared entirely, forming a morphology resembling the Widmanstätten structure. The mechanical test results show that the microhardness, tensile strength R m , yield strength R p0.2 , and elongation A of alloys all altered with increasing Al content. Among them, the R m and A of Al 0.2 CoCrFeNiMo 0.3 alloy are 656.81 MPa and 35.02 %, respectively, exhibiting a better match in terms of both properties. Meanwhile, the incorporation of Al element encourages the formation of sub-grain boundaries in the σ phase grains of the alloy, this is beneficial to design a uniformly dispersed σ phase, further to provide a theoretical basis for the practical engineering application of high-entropy alloys.