Enhanced thermal stability of pressureless liquid-phase sintered SiC ceramics via (Hf, Zr, Ta, Nb, Ti)B₂ addition

High-temperature thermal stability plays a crucial role in the structural application of pressureless liquid-phase sintered SiC (PLS-SiC) ceramics. In this paper, a PLS-SiC ceramic processed with CeO₂–Al₂O₃ as sintering additives with excellent high-temperature thermal stability was achieved by incorporating (Hf, Zr, Ta, Nb, Ti)B₂ (HEB) particles. Results showed that PLS-SiC ceramics with HEB-free underwent a structural change from dense to porous microstructure after annealing at 1800 °C/1 h. Conversely, PLS-SiC ceramics with the addition of 10 vol% HEB exhibited excellent thermal stability, as evidenced by the retention of their dense microstructure after exposure to annealing at 1800 °C/1 h. The possible primary reasons for this significantly different response to the thermal stability could be probably attributed to fact that HEB reacted with CeAlO₃ and SiC to form solid-phase products, subsequently inhibiting the formation of gas-phase products after decomposition of CeAlO₃ alone in a high-temperature vacuum environment. In addition, the formation of a compact protective outer layer containing Hf–Ta containing diboride in PLS-SiC ceramics during the annealing process could effectively hinder the volatilization of volatile substances at a high temperature.