On microstructure and mechanical performance of AlCoCrFeMo0.5Nix high-entropy alloys

A high-entropy alloy system, AlCoCrFeMo0.5Nix, was designed based on the AlCoCrCuFeNi alloy, by replacing Cu with Mo in order to improve strength and thermal stability. Ni content was monitored to see its effect on microstructure and properties. The microstructure of AlCoCrFeMo0.5Nix alloys consists of B2, FCC, and σ phase which are all multi-element solid solutions. As nickel content increases, the constituent phases change from B2 + σ phases at x = 0 to B2 + FCC + σ phases at x = 2.0, reflecting Ni is an FCC stabilizer. The room temperature hardness of the present alloy system decreases from Hv 904 at x = 0 to Hv 404 at x = 2.0. AlCoCrFeMo0.5Nix alloys with x = 0, 0.5, 1.0, and 1.5 exhibit higher hot hardness level than that of Ni-based superalloys, In 718 and In 718 H, up to 1273 K. Furthermore, they possess the less negative value of softening coefficient (BII) at high-temperature regime as compared with those of In 718, In 718 H, and T-800. This superiority can be explained with the slow diffusion rate of vacancies in the multi-element matrix. The present alloy system has great potential in high-temperature applications.