Oxidation resistance of boron carbide-based ceramics

The effect of the content (10-15%) of Si and Al compounds on the oxidation behavior of B sub 4 C-based ceramics in air under programmed heating up to 1500 deg C was studied. Hot pressed materials in the system B sub 4 C--SiC--AlON were investigated. Microstructural examination of the ceramics indicated that the B sub 4 C grain size decreased with an increase of additive content. The number of reaction stages, oxidation mechanisms and oxidation products were determined. Oxidation started at approx /600 deg C. Up to 1200 deg C, the oxidation led to a mass gain in the samples. In the temperature range near 1200 deg C, a leveling and even a mass loss for samples with 50% additives were observed. At higher temperatures, the mass gain increased sharply. Oxidation kinetics curves confirmed the results obtained for programmed heating of specimens. Ceramics with a higher content of the SiC and AlON additives showed a much higher oxidation resistance due to the formation of a protective oxide layer. The formation of pittings after isothermal heating at 1200 deg C was observed.