Microstructure And Properties Of CoCrCuFeMoNi High Entropy Alloys

In this paper, the series of CoCrCuxFeMoNi、CrCuxFeMoyNi and CoCr0.5CuxFeyMoNi(x,y is atomic ratio of elements, no mark is 1) high entropy alloys were prepared by using high frequency induction melting facility. Adopting various analytical methods, the as-solidified microstructure, phase structure, solidification process and compression resistance were investigated, at the same time, the phase formation regularity of high entropy alloys were verified with the theoretical calculation.For CoCrCuxFeMoNi(x=0,0.1) alloys,(Fe, Co, Ni)-rich dendritic phase forms originally, and peritectic reaction and eutectic reaction take place successively. Primarily, Mo-rich dendrites nucleate in the CoCrCu0.3FeMoNi melt, and quasi-peritectic reaction occurs between the primary dendrites and liquids, then the quasi-peritectic structures are replaced by the extended eutectic couple growth to form the island-like eutectic structure. Followed that, the eutectic reaction happens in the remnant liquids. Phase separations have occurred before solidification in CoCrCuxFeMoNi(x≥0.5) alloys. Cu-rich spheres are observed in the as-solidified microstructure. phase separation has occurred in CrCuxFeMoyNi alloys, and even macroscopic phase separation are observed in the CrCuFeMoyNi alloy. The primary dendritic phase of CoCr0.5CuxFeyMoNi alloys are all rich of Mo element. The quasi-peritectic reaction and eutectic reaction occurred in CoCr0.5Cuo.1FeyMoNi alloys. The island-like eutectic structure and layer eutectic structure are observed in CoCr0.5Cu0.3FeyMoNi alloys.The microstructure of as-solidified CoCrCuxFeMoNi and CoCr0.5CuxFeyMoNi alloys are consisted of FCC and BCC solid solution. However, BCC solid solution is replaced by σ phase in CrCuxFeMoyNi alloys.In CoCrCuFeMoNi high entropy alloys, phase separation occurs when ΔHmix>0. The ΔR, ΔX and ΔS of the investigated alloys are conformed to the theory criterion proposed by Guo et al.Due to phase separation liquid alloy will form the two liquid with different components, which are different from the equilibrium liquid phase. The VEC has been calculated by the original liquid cannot reflect the real situation. So the theory criterion(VEC) of formation the FCC and BCC phase mixing can not be applied to the high entropy alloys which have a tendency of phase separation.For CoCrCu0.1FeMoNi alloy, the compressive strength and plastic strain are as high as 3012 Mpa and 51.6 %.