On the Development of Equiaxed Microstructures in High-Entropy Superalloys and Their Impact on High-Temperature Oxidation Behavior

High-Entropy Alloys (HEAs) are an exciting area of research for metallurgists seeking to push through the temperature limits of the traditional nickel- and iron-based superalloys. The HEA design principal is to suppress the formation of low-symmetry phases and maintain a solid solution through the elevated entropy of mixing which is a result of alloying at least four principal elements. Despite early promise, this solid solution-strengthened subsection of HEAs is quite limited in improved operational capacity over dilute alloys with respect to temperature and mechanical behavior. High-Entropy Superalloys (HESAs) refer to those multiple-principal element materials which exhibit secondary strengthening phases such as γ′ which has historically allowed nickel-based superalloys to operate near their melting temperatures. As this alloy space is surveyed with arc-melted castings in a high-throughput fashion, potential alloy candidates may be prematurely dismissed based on oxidation behavior without consideration of microstructural uniformity. The Gleeble 3500D thermomechanical simulator was used to develop optimal working parameters for hot thermomechanical processing (HTMP) of the Ni47.5Fe13Co11Al12Cr10Ta4Ti2.5 HESA and create multiple thermogravimetric oxidation specimens. These HTMP samples were compared to solely homogenized specimens and were found to exhibit measurably slower oxidation rates as well as decreased variability in their final performance.