The peculiarities in oxidation behavior of the ZrB₂-SiC ceramics with chromium additive

ZrB₂-SiC-Cr powder sintering at 1600 °C and its oxidation behavior at 1000–1500 °C in air were studied as a function of chromium content. It was shown that the relative density of the ZrB₂-SiC ceramics increases with an increase in chromium content in the powdered mixture. This is related to the formation of the liquid Cr-Si-C-B phase during the high-temperature interaction of SiC with chromium and ZrB₂. It was stated that the mechanism of ZrB₂-SiC-Cr ceramics oxidation is changed from bulk to passive. The oxidation resistance is improved for the ceramics with 13% of chromium or less, which can be explained by a decrease in its porosity. The ceramics with higher chromium content demonstrates the opposite effect, namely, large-size Cr₂O₃ crystals are formed during oxidation, this promotes microcracking in the oxidizing layer and causes damage of surface integrity. As a result, the oxidation resistance of the ZrB₂-SiC-Cr ceramics with high chromium content is decreased.