A Novel Nanostructured Mullite Feedstock for Environmental Barrier Coatings via Atmosphere Plasma Spraying

A novel strategy is proposed to design an exclusive nanostructured mullite spherical feedstock for environmental barrier coatings (EBCs) via atmosphere plasma spraying (APS). The nanostructured mullite spherical feedstocks are successfully obtained by the procedure of spray drying, solid-phase sintering and flame spheroidization. The crystal grain size of nano-mullite increases with annealing temperature. When the temperature is as high as 1500^◦C, the reaction of Al₂O₃ and SiO₂ can be fully completed. The average size is 52 nm for the grain of mullite in feedstocks sintered at 1500^◦C, which can be reduced from 52 nm to 48 nm by flame spheroidization treatment as well. Meanwhile, the nanostructured spherical feedstocks show high density and good flowability, which is suitable for APS. The mullite coatings is successfully prepared on a SiC substrate by APS, in which both the nanoscale crystals and nanostructures are perfectly kept as designed. Furthermore, there is no crack appeared in the nanostructured mullite coatings. Thus, the nanostructured mullite feedstock is one of promising candidates for the high performance EBCs.