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Abstract
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A comprehensive literature review on recently rediscovered Co- and/or CoNi-based superalloys, strengthened by the γ' phase, revealed a relationship between the configurational entropy of the system and the γ' 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 γ' solvus temperature, the configurational entropy should be increased by adding γ' 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.
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