Microstructural Evolution and Hardness of CoxCrCuFeNi High-Entropy Alloys

The effects of Co contents on the microstructure characteristic and phase structure of CoxCrCuFeNi high-entropy alloys were investigated by SEM, EDS and XRD. The microstructures consisted of dendrites and many nanoprecipitations in the interdendritic. Increase Co contents,the size of nanoprecipitated phase in the interdendritic firstly increased and then decreased slightly. According to XRD analysis, two simple FCC phases, dendrite phase and Cu-rich interdendritic phase were found. As a result of slow diffusion, supersaturated solid solution was formed during solidification and then nanophase was precipitated during the following cooling process. The results of EDS revealed that Fe、Co and Cr were rich in dendrites, while Cu was rich at the interdendritic. For element Ni, which was rich in dendrites when x≤1.0, but was almost the normal value in dendrites for x>1.0. The reason for segregation was related to the positive mixing enthalpy between elements. The contents of Co had little impact on the hardness of CoxCrCuFeNi high-entropy alloys according to micro-hardness testing.