An oxidation-resistant environmental barrier coating with a dense and highly crystalline structure via high temperature LPPS

Environmental barrier coatings (EBCs) are essential for protecting SiC-based composites against water vapor-rich combustion environments in advanced gas turbine engines. During service, rapid oxidation, reflected as thickening in the silica-thermally grown oxide layer (SiO₂-TGO), often causes EBC failure. A key solution for durable EBC is to lower the oxidation rate of TGO. This study obtained an oxidation-resistant ytterbium disilicate (YbDS) EBC with a dense and highly crystalline structure to prevent rapid ingress of oxygen and water vapor. First, it demonstrates that deposition temperature fundamentally determines the as-sprayed density, crystallinity, and subsequent oxidation behavior. Low-temperature (∼700 ℃) results in a predominantly amorphous microstructure, which crystallizes during high-temperature service, inducing volumetric shrinkage and forming pores and microcracks. Although these defects can partly heal through surface-energy-driven densification in dry air, water vapor changes the mechanism to a reaction-driven mass loss, reducing healing rate by over 70% and accelerating oxidation. Conversely, high-temperature-deposited coatings (∼1000 ℃), with approximately 98% crystallinity and no post-annealing, avoid crystallization-induced stresses and maintain excellent structural integrity with low crack density during water vapor exposure. Consequently, this dense and highly crystalline structure slows SiO₂-TGO growth by ∼60% and extends oxidation resistance life by a factor of 8. Therefore, achieving a dense microstructure with high crystallinity during deposition is critical for developing oxidation-resistant and durable coatings.