  A comprehensive literature review on recently rediscovered Co- and/or
CoNi-based superalloys, strengthened by the {\gamma}' phase, revealed a
relationship between the configurational entropy of the system and the
{\gamma}' solvus temperature. This study was conducted on a high Cr CoNi-based
superalloy system with high configurational entropy to test our hypothesis
based on the sustainable metallurgy framework. Thermodynamic calculations were
performed to design the chemical compositions, followed by vacuum casting and
heat treatments to produce the desired alloys. The microstructures were
characterized using a scanning electron microscope, electron backscattered
diffraction, transmission electron microscope, and differential thermal
analysis. Microhardness and nanoindentation tests were employed to measure the
mechanical properties. The results showed that both the configurational entropy
and the type of alloying elements determine the final high-temperature
performance of the alloys. We found that to enhance the higher {\gamma}' solvus
temperature, the configurational entropy should be increased by adding
{\gamma}' stabilizing elements. The microstructural and mechanical
characteristics of the designed alloys before and after heat treatments are
discussed in detail. The outcome of this study is beneficial for developing
cobalt-based high-entropy superalloys with appropriate processing windows and
freezing ranges for advanced sustainable manufacturing purposes, such as using
powder bed fusion technologies.
