Studies On Correlation Between Microstructure And Properties Of AlCoCrCuFeMoNi Multicomponent High Entropy Alloys

Mutilcomponent high entropy alloys CoCrFeMoNi,Co CrCu0.1FeMoNi and AlCoCrCu0.1FeMoNi were designed on the basis of composition design principles. All ingots were prepared by vacuum arc furnace smelting, and the as-solidified microstructures and compositions of alloys were studied by using SEM equipped with EDS. The crystalline structure of alloys was characterized using X-ray diffraction(XRD). At the same time, the hardness and compressive property were tested on the microhardness tester and universal testing machine.The crystal structures of CoCrFeMoNi and CoCrCu0.1FeMoNi high entropy alloys are all identified as multiphase structure, meaning that the constituent phases are FCC, BCC solid phase and TCP phase. As the molar ratio of Mo decreases, phase structure of all alloys tends to be simple, and simple FCC solid-solution structure is detected when the molar ratio of Mo reaches to 0.3. The hardness of CoCrFeMoNi and CoCrCu0.1FeMoNi high entropy alloys as a function of x value is shown as a descending trend. CoCr1.5FeMo0.5Ni and Co1.5CrCu0.1FeMo0.5Ni alloys exhibit good properties with the high compressive fracture strength about 1980 MPa and 2850 MPa, and proper plastic strain about 56% and 62%, respectively.The as-solidified microstructure of AlXCoCrCu0.1FeMo1-XNi alloys transform from the dendrites and interdendritic eutectic microstructure to eutectic microstructure, then to the dendrites and interdendritic eutectic microstructure. When x value is up to 1.0, petals structure appears in AlCoCrCu0.1FeNi alloy. Only three crystal structures: FCC, BCC and TCP(Laves,?) are identified. When x value is 0.2, BCC phase arises. And Laves phase disappears with x value is more than 0.5. The room-temperature hardness of AlCoCrCu0.1Fe MoNi alloys maintain at 300-700 HV, it presents increasing firstly then decreasing. Al0.8CoCrCu0.1FeMo0.2Ni alloy reveals a better comprehensive mechanical property. And its yield strength, compressive strength and hardness are 620 MPa, 880 MPa and 592.5HV respectively. Meanwhile, plastic strain is about 37%.Co20Cr24Fe20Mo16Ni20 alloy is the eutectic composition of CoCrFeMoNi high entropy alloys; And CoCrCu0.1FeMoNi high entropy alloys contain at least two eutectic points, one is CoCr1.5Cu0.1FeMo0.5Ni alloy and the other is CoCrCu0.1Fe1.2Mo0.8Ni alloy. It indicates that, increasing of Co, Fe and Ni content contributes to the formation of FCC phase, and BCC phase is preferred with the increasing of of Cr and Al, while Mo content is helpful to the formation of BCC and topological close packed phase. The alloy with larger FCC volume fraction usually has a better plasticity, and the alloy with larger BCC and TCP volume fraction has high yield strength but poor plasticity. According to phase formation prediction and calculation results of the alloy, the values of mixing enthalpy, mixing entropy, atomic radius differences of the alloys are within a reasonable range of the phase formation. When valence electron concentration and the electronegativity difference are in 8 and 0.133 ups and downs, the alloy still contains FCC, BCC structure and TCP phase.