Ytterbium Silicate Environmental Barrier Coatings Deposited Using the Solution-Based Precursor Plasma Spray

Abstract

Gas turbine efficiency can be improved by increasing the operating temperature and by reducing the need for cooling air, both of which are enabled by higher temperature materials. Silicon carbide based ceramic matrix composites (CMCs) have shown promise for achieving higher temperatures. However, to survive in the high-temperature high-humidity combustion environment, environmental barrier coatings (EBCs) are essential to limit silicon loss of CMCs and its associated damage. Atmospheric plasma spray (APS) is a popular process for making such coatings. In this work, an alternative deposition process is explored, specifically the solution precursor plasma spray (SPPS), where it will be shown for ytterbium monosilicate EBCs that such process directly deposits thin (< 50 μm), dense and crystalline EBC topcoats without annealing of amorphous phases as is needed in the APS process. In addition, the SPPS process allows for quick compensation of system-specific element loss observed in both SPPS and APS processes. Finally, the secondary phase present in EBCs are much smaller in size for the SPPS process and hence less likely to produce cracking compared to APS EBCs.