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

Though the strengthening effect of σ and μ 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 °C for 7 days and 1080 °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 σ and μ 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 σ and μ phases and their selections.