Oxidation Resistance and Microstructural Analysis of Polymer-Derived (HfxTa1−x)C/SiC Ceramic Nanocomposites

The oxidation behavior of polymer-derived (Hf<inf>x</inf>Ta<inf>1−x</inf>)C/SiC nanocomposites at 1200 °C and 1400 °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 (Hf<inf>0.2</inf>Ta<inf>0.8</inf>)C/SiC to (Hf<inf>0.7</inf>Ta<inf>0.3</inf>)C/SiC results in an improved oxidation behavior due to Hf<inf>6</inf>Ta<inf>2</inf>O<inf>17</inf> formation and the reduction of Ta<inf>2</inf>O<inf>5</inf> formation, which reduces cracking of the samples. The formation and microstructure of SiO<inf>2</inf> as well as the internal oxidation of (Hf<inf>x</inf>Ta<inf>1−x</inf>)C precipitates is explained by thermodynamic and kinetic considerations.