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, reflecting as thickening in silica-thermally grown oxide layer (SiO2-TGO), often results to failure of EBCs. Therefore, a key solution for durable EBC is to lower oxidation rate of TGO. This study obtained an oxidation resistant ytterbium disilicate (YbDS) EBC by 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 °C) results in a predominantly amorphous microstructure, which crystallizes during high-temperature service, inducing volumetric shrinkage and the formation of pores and microcracks. Although these defects can partially heal through surface-energy-driven densification in dry air, the presence of water vapor alters the mechanism to a reaction-driven mass loss, reducing the healing rate by over 70% and accelerating oxidative ingress. In contrast, the high-temperature-deposited coating (~1000 °C), with approximately 98% crystallinity, avoids crystallization-induced stresses, maintains excellent structural integrity with a low crack density during water vapor exposure. As a result, this dense and highly crystalline structure slows the growth rate of SiO2-TGO by ~60%, and extends the 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.