Significant improvement of the short-term high-temperature oxidation resistance of dense monolithic HfC/SiC ceramic nanocomposites upon incorporation of Ta

The short-term oxidation (i.e., exposure time of up to 20 h) of dense monolithic (Hf,Ta)C/SiC-based ceramic nanocomposites at temperatures from 1200 to 1500 degrees C is presented and discussed. The oxidation behavior of HfC/SiC is similar to that of other UHTCs, indicating that it is mainly determined by the HfC phase. Ta incorporation into HfC leads to a strong decrease of the parabolic oxidation rates (3-4 orders of magnitude). Unlike HfC/SiC, Ta-containing nanocomposites form continuous multiphasic scales consisting of HfO2, Ta2O5 and Hf6Ta2O17, which are able to densify quickly during the oxidation process.