Synthesis and Properties of Compositionally Complex Ultra-High-Temperature Ceramics

Ultra-High Temperature Ceramics (UHTCs) are promising materials for use in next-generation hypersonic platforms owing to their high melting points and excellent thermo-mechanical properties.One exciting aspect of UHTCs is that increasing the complexity of their composition leads to substantial property enhancements. For instance, refractory carbides (HfC, TaC, etc.) possess high mutual solubility and can be fabricated as compositionally complex carbides (e.g., HfNbTaTiZrC₅), which exhibit >50% increase in hardness over their individual constituents. However, the role of composition is muddled with stoichiometric departures associated with excess vacancy concentrations. In this talk, we will present a novel synthesis route to fabricating these materials by exposing precursor metallic alloys to reactive gases at elevated temperature, which enable the stoichiometry to be precisely controlled. In addition, this talk will address the governing kinetics of their synthesis, and their resulting mechanical and high-temperature oxdiation properties.