Opportunities for novel refractory alloy thermal/environmental barrier coatings using multicomponent rare earth oxides

Opportunities are described for developing coatings for refractory alloys beyond the current state-of-the-art silicide coatings, which are inadequate for long-term application in combustion environments due to silica volatility. It is proposed that multicomponent rare earth oxides provide an ideal material system to tailor all necessary properties for environmental/thermal barrier coatings in a single layer, differing from current trends to adopt multi-layer systems that are prone to thermochemical-mechanical interface failure mechanisms. The article discusses opportunities, proof-of-concept, and challenges to accomplish these single-layer rare earth oxide coatings. Properties of interest include isotropic phase stability, processability, thermal expansion, thermal conductivity, ability to perform as a radiation barrier, stability in combustion environments, CMAS resistance, and ability to act as an oxygen diffusion barrier. Both experimental and computational approaches for property optimization are described.