Revealing the Selection of σ and μ Phases in CoCrFeNiMo x High Entropy Alloys by CALPHAD

Though the strengthening effect of sigma and mu phases in CoCrFeNiMo (x) high entropy alloys has been confirmed, the selection of these two phases remains unclear, which restricts the further strengthening design. In this study, microstructures and phase compositions of CoCrFeNiMo (x) (x = 0.1, 0.2, 0.3, 0.4, and 0.5) alloys were investigated through annealing at 600, 750, 900, 1000 A degrees C for 7 days and 1080 A degrees C for 3 days, respectively. Based on the experiment results, a (CoCrFeNi)-Mo phase selection diagram was drawn and compared with the calculated isopleth phase diagram of (CoCrFeNi)-Mo. The results indicate that the selection of sigma and mu phases depends on the content of Mo greatly. Due to the limited prediction of phase selection and transformation by the isopleth phase diagram of (CoCrFeNi)-Mo, we design a (CoFeNi)-Mo-Cr isothermal phase diagram to reveal the transformation between sigma and mu phases and their selections.