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

CERAMICS INTERNATIONAL(2024)

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Abstract
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 degrees 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 degrees 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.
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Key words
SiC,Pressureless liquid-phase sintering,Thermal stability,High-entropy diboride
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