Influence of different liquid phase sintering aids on the oxidation resistance of UHTCMCs with a ZrB2 matrix

ZrB 2 -based Ultra-High Temperature Ceramics (UHTCs) are promising materials for aerospace applications due to their excellent thermal and mechanical properties. However, their oxidation resistance above 1200 °C is limited by the formation of volatile B 2 O 3 and porous ZrO 2 , compromising long-term stability in extreme environments. This study investigates the oxidation behaviour of carbon fibre-reinforced ZrB 2 -SiC composites, fabricated via slurry impregnation and hot pressing, with different Liquid Phase Sintering (LPS) aids to enhance oxidation resistance. The composites, consisting of 40 vol.% carbon fibre, 42 vol.% ZrB 2 , 6 vol.% SiC, and 12 vol.% LPS aids (Si 3 N 4 , Y 2 O 3 , ZrSi 2 , and Si 3 N 4 ·B 2 O 3 ), were tested in air at 1650 °C for up to 30 minutes. The results showed that, although all selected liquid-phase sintering (LPS) aids decreased sintering temperature of C/ZrB 2 -SiC, Y 2 O 3 disrupted the formation of a protective borosilicate-based glassy scale, increased oxygen diffusion, and accelerated material degradation. ZrSi 2 was found to be the best compromise to promote both densification and good oxidation resistance. • Si 3 N 4 , Si 3 N 4 +B 2 O 3 and ZrSi 2 resulted in higher SiC content and similar behaviour at 1650°C • The protective mechanism of SiC-yielding aids was the formation of a continuous silica glass • Y 2 O 3 led to catastrophic oxidation due to formation of low viscosity and unstable liquid phases • ZrSi 2 was identified as the best compromise to promote densification and oxidation resistance