Microstructure control and micromechanical property enhancement of CoCrFeNiZr_0.5 alloy under melt quenching and electrostatic levitation conditions

The mechanism of microstructure evolution during rapid solidification and the proactive regulation of phase constitution to optimize the micromechanical properties of multicomponent alloys have been the focus of research in recent years. In this paper, the evolution of microstructural growth kinetics and the formation of amorphous phase in CoCrFeNiZr_0.5 alloy were achieved by melt spinning technique and electrostatic levitation coupled melt quenching. According to the theory of transient nucleation, the nucleation incubation time of Laves, FCC, Fe₂₃Zr₆ and BCC phases with undercooling during rapid solidification of the alloy was calculated. And based on this, the mechanism of phase transition in the process of regular eutectic → anomalous eutectic → nanocrystalline → amorphous composite → complete amorphous structure was discussed and explained. The growth behavior of primary and eutectic phases solidified at different undercoolings was investigated. Combined with melt quenching, the alloy melts were quenched in the superheated state, liquidus, undercooled state and recalescence process. Multiple microstructures, including amorphous structure, amorphous plus nano-eutectic, gradient nano-eutectic and composite structure of primary Laves phase, along with primary eutectic plus secondary quenched eutectic structures were obtained, respectively. Moreover, the shear band and free volume theory were applied to explain the deformation behavior and the discrepant mechanical performance between amorphous composites and amorphous structures. The formation of quenched nano-eutectic and amorphous structure not only improves the hardness of the alloy, but also enhances the fracture toughness.