Empirical and Computational-Based Phase Predictions of Thermal Sprayed High-Entropy Alloys

Due to the wide range of compositional possibilities in the high-entropy alloy (HEA) field, empirical models and the CALPHAD method have been implemented to efficiently design HEAs. Although most design strategies have been tested on as-cast alloys, their validation for thermal sprayed HEA coatings is lacking. In this work, empirical models and the CALPHAD method under equilibrium and non-equilibrium conditions are assessed for phase prediction in five HEAs in the as-cast, laser clad and thermal sprayed conditions. High-velocity oxygen fuel coatings were prepared for these five HEAs, and their phases were identified by the x-ray diffraction analysis. These processes, even though their cooling rates vary significantly, show similar phase formation as indicated by a literature review and the current experimental study. The CALPHAD equilibrium calculation predicted most of the phases at specified temperatures. Furthermore, the CALPHAD-based non-equilibrium simulations correctly predicted the major phases present in the HEA coatings. The empirical models also show good prediction capability, but the intermetallic sigma phase is problematic for the parameter-based models. Therefore, the CALPHAD method can be used to efficiently design and develop HEAs prepared under conditions that encompass rapid cooling, such as occurring during thermal spray processes.