| Summary: | In the present work, we reported the microstructure and mechanical properties of CrxMnFeNi high-entropy alloy (HEA). The microstructures of the HEAs were characterized by scanning electron microscopy (SEM) with electron back-scattered diffraction (EBSD) and energy dispersive spectrometer (EDS) system, X-ray diffraction (XRD), and transmission electron microscopy (TEM). Mechanical properties of the HEAs were measured by nano-indentation and tensile test. The results showed that the single face-centered cubic (FCC) structure was transformed into the FCC and body-centered cubic (BCC) dual-phase when the Cr content was higher than the threshold value. Also, in the dual-phase HEAs, the fraction of the BCC phase increased proportionally with the increasing Cr content. There was an excellent correlation between the phase composition and the corresponding concentration of the valence electron concentration (VEC). The single FCC phase structure alloy demonstrated lower yield strength and higher tensile ductility. In the dual-phase alloys, the presence of the BCC phase notably strengthened the alloy but deteriorated its ductility. The close relationship between the mechanical properties of the alloy and each phase and the effect of the FCC/BCC dual-phase were discussed. It was confirmed that the grain refinement and higher Hall–Petch strengthening coefficient caused by the BCC phase formation showed a good strength-ductility matching mechanism in the dual-phase alloys.
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