Microstructure and reaction mechanism of SiC ceramic with mullite-zircon as a new liquid-phase sintering additives system

Mullite-zircon (Al2O3–SiO2–ZrSiO4), as a new liquid-phase sintering (LPS) additives system, was introduced into the silicon carbide (SiC) ceramics in order to improve the mechanical and thermal shock properties. The reaction mechanism of the SiC ceramics with additive system during the sintering process was analyzed by thermodynamic calculation and the mullite-zircon system was detected as expected in the final specimens. The ZrSiO4 phase was generated from the reactions of ZrB2 and SiO2 in air and distributed homogeneously in the SiC matrix. The mullite phase in the form of crystal whisker was completely crystallized at 1350 °C, and the size of the crystallite increased with the increase of the sintering temperature from 1350 °C to 1400 °C. This process was explained by vapor–liquid–solid (VLS) mechanism. The influences of sintering temperature and the content of ZrB2 content on their properties and the reaction mechanism were studied. It was found that the specimens were compact when sintered at 1400 °C, and the content of ZrB2 played an important role in the densification process.