High-temperature behavior and self-enhancing mechanisms of oxide-bonded SiC porous ceramics

Oxide-bonded SiC porous ceramics (SCPCs), synthesized via reaction bonding, exhibit significant potential for high-temperature applications. However, incorporating sintering aids inevitably results in a considerable quantity of amorphous glass phase within SCPCs, thereby introducing risks to their high-temperature mechanical performance. In this study, we employ in-situ characterization techniques to investigate the high-temperature behavior of SCPCs. Our findings reveal that SCPCs demonstrate remarkable high-temperature self-enhancing properties, with a critical bending strength at 800 degrees C. Beyond this temperature, the strength declines sharply. Intriguingly, the critical bending strength is 36.6% greater than at ambient temperature. Moreover, elevated temperatures enhance the elastic modulus and promote the transition of SCPCs from multilinear to nonelastic fracture. The neck phase, which imparts strength to the SCPCs, is composed of four distinct layers along the depth direction: silicate glass, oxygen-containing, silicon-rich, and SiC region, as revealed by FIB-TEM. The transformation from alpha to beta-cristobalite in the oxygen-containing region improves the thermal expansion match with SiC, thereby mitigating local stress concentration. Furthermore, the compressive stress within the neck region intensifies with increasing temperatures, thereby inhibiting crack propagation. This work provides a basis for the high-temperature applications of SCPCs.