Development of Oxidation Resistant Refractory High Entropy Alloys for High Temperature Applications: Recent Results and Development Strategy

Refractory High Entropy Alloys (HEAs) can be considered as promising materials for high temperature applications because of their high melting point and outstanding high temperature strength. The microstructure of the equimolar alloy Nb-Mo-Cr-Ti-Al consists of a disordered body centered cubic (BCC) phase and a small amount of the Laves phase, while the equimolar alloy Ta-Mo-Cr-Ti-Al exhibits the ordered B2 and several Laves phases in addition to the BCC phase. The experimental studies reveal that these alloys possess a beneficial combination of high temperature strength and corrosion protectiveness. The compressive yield stress of the alloy Nb-Mo-Cr-Ti-Al and Ta-Mo-Cr-Ti-Al at 1200 °C is determined to 100 MPa and 200 MPa, respectively. The oxidation resistance of the alloy Ta-Mo-Cr-Ti-Al in the temperature range between 900 and 1100 °C is comparable to that of multi-phase Ni-based alloys. The main drawback of both alloys is their low ductility at room temperature. Strategies for the future alloy development are discussed.