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.