Characterization models for thermal shock resistance and fracture strength of ultra-high temperature ceramics at high temperatures

In this work, based on the traditional fracture mechanics theory and the fracture thought at high temperatures, the thermal shock resistance models for the ultra-high temperature ceramics (UHTCs) considering combined effects of temperature and microstructures are developed. The effects of microflaws including cracks and pores, grains and residual stress due to thermal expansion anisotropy on the thermal shock resistance and their evolution with increase of temperature are studied in detail. The study shows that there exists a dangerous zoon of temperature according to the much lower critical temperature difference of rupture of UHTCs. While introducing the micropores with suitable content and feature size into a UHTC significantly increases the thermal shock resistance of the material, and can eliminate the dangerous zone of temperature for thermal shock resistance. A temperature dependent fracture strength model for UHTCs is proposed. Excellent agreement is obtained between model predictions and experimental data. This work shows a method for quantitatively estimating effects of microstructures on the thermal shock resistance and fracture strength of UHTCs at high temperatures.