The emergence of Co- or CoNi-based superalloys in 2006 and high entropy alloys in 2004 have garnered immense attention from the materials community, as they offer the potential to design and develop high-temperature and high-strength alloys beyond the matured Ni-based superalloys. In this study, we utilized thermodynamical calculations, specifically the CALPHAD method, based on the lever rule, Gulliver-Scheil, and multicomponent phase diagram, to develop a CoNi-based high entropy superalloy (HESA). The accuracy of the CALPHAD method was verified through casting and heat treatment. Powder of the designed composition was then produced using gas atomization and consolidated using spark plasma sintering (SPS) and powder bed fusion – laser beam (PBF-LB). Advanced characterization techniques such as double-beam scanning electron microscopy equipped with electron backscatter diffraction (EBSD) and energy dispersive spectroscopy (EDS), density measurements, and micro-hardness testing were used to analyze the microstructure and physical and mechanical properties of the as-built alloys. Fully dense parts with relative density of greater than 99.9% obtained through SPS and PBF-LB and the results indicated that the microstructure of the as-built alloys is consistent with the predictions made by CALPHAD calculations, with a single-phase fcc structure and no secondary phases. However, in the case of the as-cast alloy, a small amount of beta phase (≈2.5%) was detected, which necessitated homogenization and subsequently led to abnormal grain growth after heat treatment.
