Effect of TaC additions on the oxidation behaviour of ZrB2-SiC-AlN ultra-high temperature ceramics at 1600 °C

The effect of TaC additions on the oxidation behaviour of ZrB 2 -SiC based ultra-high-temperature ceramics, with and without AlN, was evaluated at 1600 °C in stagnant air. Three spark-plasma-sintered compositions were studied: ZSA721 (70ZrB2-20SiC-10AlN), ZSAT72-5-5 (70ZrB 2 -20SiC-5AlN-5TaC), and ZST631 (60ZrB2-30SiC-10TaC). After 10 h, ZSA721 gained 58 mg cm -2 and formed a 1388 ± 100 μm oxide layer. Partial replacement of AlN by TaC lowered the mass gain to 45 mg cm -2 and produced a thicker SiO 2 -rich surface layer, but the total oxide thickness remained comparable at 1357 ± 100 μm, while the SiC-depleted zone increased from 156 ± 12 to 240 ± 15 μm. To promote SiO 2 formation further, we increased the SiC content (ZST631); however, oxidation of ZST631 resulted in the highest mass gain (69 mg cm -2 ), the thickest oxide layer (1477 ± 200 μm) and a discontinuous SiO 2 scale. Our results, when contextualized with the research literature, indicate that TaC promotes cooperative degradation, potentially through porosity created by gas-evolution and restricted lateral spreading and healing of the Ta-containing borosilicate glass, thereby hindering the oxidation resistance.