High Energy X-ray Investigation of Ultra-High Temperature Ceramics under Thermal Cycling

Ultra-high temperature ceramics (UHTCs) are ideal candidate material compositions to protect aircrafts, systems, and other vehicles within the hypersonic regime. More specifically, hafnium carbides (HfC) and tantalum carbides (TaC), are favorable UHTC candidates due to their extremely high melting temperatures, even compared to other UHTCs. The effects of thermal cycling during operation as well as the effects of oxidation must be fully elucidated for reusable hypersonic vehicle applications. In-situ high energy X-ray diffraction from a synchrotron was utilized to capture these thermal cyclic effects and oxide formation while HfC, TaC, and 10 vol% HfC + TaC samples were above the oxidation temperature point. The grain sizes of all samples, regardless of variation in the manufacturing parameters, became smaller throughout cycling as the HfC and TaC decomposed and oxidized to form HfO₂ and Ta₂O₅. The TaC samples had the highest oxidation while the 10 vol% HfC + TaC sample appears to be more resistant to oxidation. These results suggest creating a mixture of the two carbides might reduce overall oxidation rates and increase the longevity of the UHTC throughout hypersonic flight and potentially viable for reusable hypersonic applications when coupled with additional oxidation mitigation strategies.