Oxidation Resistance and Microstructural Analysis of Polymer-Derived (Hf_xTa_1-x)C/SiC Ceramic Nanocomposites

The oxidation behavior of polymer-derived (HfxTa1-x)C/SiC nanocomposites at 1200 degrees C and 1400 degrees C for up to 100 h is investigated in this work. Overall, the chemical modification of the polycarbosilane-based precursor with Hf and Ta leads to an improved oxidation behavior due to an increased densification. Shifting the Hf/Ta ratio from (Hf0.2Ta0.8)C/SiC to (Hf0.7Ta0.3)C/SiC results in an improved oxidation behavior due to Hf6Ta2O17 formation and the reduction of Ta2O5 formation, which reduces cracking of the samples. The formation and microstructure of SiO2 as well as the internal oxidation of (HfxTa1-x)C precipitates is explained by thermodynamic and kinetic considerations.