Searching the limits of compositionally complex AlB2-type diboride solid solutions for hypersonic applications

Compositionally complex (CC) AlB2-type diboride solid solutions (DSSs) containing IV-V-VI group metals were investigated as candidate materials for hypersonic applications using a ground entry simulator. Each CCDSS was composed of Ti and three other transition metals among Zr-Hf-Nb-Ta. Single phase CCDSS dense discs were spark plasma sintered and then exposed to a supersonic dissociated airflow (nominal Mach 3). The overall degradation of the discs was highly dependent on the combination of starting metals, and massive preferential oxidation occurred. The coexistence of Nb and Ta was detrimental. A thermal study was devised and implemented in a numerical model to validate the experimental set-up. The experimental results also showed good agreement with predictions based on a thermodynamic assessment.