A thermo-damage strength model for the SiC-depleted layer of ultra-high-temperature ceramics on high temperature oxidation

At high temperatures above 1650°C, the SiC-depleted layer of ultra-high-temperature ceramics which has high porosity appears during the oxidation process. In this present paper, based on the studies of the oxidative mechanisms and the fracture mechanisms of ultra-high-temperature ceramics under normal and high temperatures, a thermo-damage strength model for the SiC-depleted layer on high temperature oxidation was proposed. Using the model, the phase transformation, microstructure development and fracture performance in the SiC-depleted layer on high temperature oxidation were studied in detail. The study showed that the porosity is mainly related to the oxidation of SiC. And while the SiC is substantially completely oxidized, only a very small part of matrix is oxidized. The fracture strength of the SiC-depleted layer degrades seriously during the high temperature oxidation process. And the bigger the initial volume fraction of SiC, the lower the fracture strength of the SiC-depleted layer is. This layer may become the origin of failure of material, thus the further researches should be undertaken to improve the oxidation behavior for the ultra-high-temperature ceramics in a wider temperature range.