Effect of molybdenum on phases, microstructure and mechanical properties of Al0.5CoCrFeMoxNi high entropy alloys

Effect of molybdenum on phases, microstructure and mechanical properties of Al0.5CoCrFeMoxNi (x = 0 -0.5 mol) high entropy alloys has been investigated in this paper. The microstructure, phase constituents and mechanical properties of the alloys have been studied using scanning electron microscopy, X-ray diffraction, transmission electron microscopy, compressive and hardness tests. The possible equilibrium phases existing in the alloys have also been evaluated using the Thermo-Calc program. The as-cast Al0.5CoCrFeMoxNi alloys have typical dendrite microstructure. The alloys with x = 0 and 0.1 consist of FCC and (Ni, Al)-rich ordered BCC phase, while the other four alloys are composed of FCC, (Ni, Al)-rich ordered BCC phase and (Cr, Mo)-rich sigma phase. The thermodynamic calculation shows that Mo changes the phase formation order, mole fraction and composition of the equilibrium phases in the Al0.5CoCrFeMoxNi alloys. The addition of Mo enhances formation of sigma phase in the Al0.5CoCrFeMoxNi alloys, improves the hardness and compressive strength of as-cast alloys, and reduces the ductility of the alloys. The Al0.5CoCrFeMo0.3Ni and Al0.5CoCrFeMo0.4Ni alloys have balanced properties of compressive strength and ductility. Al0.5CoCrFeMo0.3Ni alloy has a sigma(0.2) of 814 MPa, an ultimate strength of 2101 MPa, and a fracture strain of 31%, while Al0.5CoCrFeMo0.4Ni alloy has a sigma(0.2) of 1091 MPa, an ultimate strength of 2117 MPa, and a fracture strain of 18%. (c) 2018 Elsevier B.V. All rights reserved.