Solid-Solution Effects on the High-Temperature Oxidation Behavior of Polymer-Derived (Hf,Ta)C/SiC and (Hf,Ti)C/SiC Ceramic Nanocomposites

In the present study, two concepts to improve the oxidation resistance at high-temperatures of ceramic nanocomposites consisting of 85-90 vol% SiC, 5-8 vol% group IV metal carbides (i.e., HfC, TaC), and 5-7 vol% carbon are introduced and discussed. First improvement concept relates to the passivation of the samples upon short-term oxidation at 1400 degrees C (30 min). This is a critical step, especially with respect to silica formation, which is relatively sluggish at temperatures lower than 1000-1200 degrees C. Moreover, solid-solution metal carbides (Hf,Ta)C and (Hf,Ti)C are shown to be clearly more oxidation resistant than the binary HfC and TaC phases. Whereas, the solid-solution effect contributes to a significant improvement of the short-term oxidation resistance of the studied nanocomposites, the passivation of the materials prior exposure of high-temperature oxidation conditions provides a remarkably improved long-term behavior thereof. Possible mechanisms involved in the oxidation processes of (Hf,Ta)C/SiC and (Hf,Ti)/SiC ceramic nanocomposites are highlighted and critically assessed.