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.

Automated summary

The empirical models and the CALPHAD method were assessed for phase prediction in HEAs under equilibrium and non-equilibrium conditions. The CALPHAD method showed good prediction capability for the phases in the HEA coatings, especially under rapid cooling conditions.