Thermal cycling and steam corrosion behavior of Yb3Al5O12-based multilayered environmental barrier coatings for SiCf/SiC

To alleviate thermal mismatch problem of environmental barrier coatings (EBCs) on SiC fiber-reinforced SiC ceramic matrix composites (SiCf/SiC CMCs) surface and improve their high-temperature durability for aircraft engines, by fully utilizing the appropriate thermal expansion coefficient, low oxygen transmittance, low thermal conductivity, and other advantages of ytterbium aluminum garnet (Yb3Al5O12), the double ceramic layered Yb3Al5O12/Yb2Si2O7 (DCL-Yb3Al5O12) and the triple ceramic layered Yb3Al5O12/Yb2SiO5/Yb2Si2O7 (TCL-Yb3Al5O12) EBC systems were prepared on SiCf/SiC CMCs by atmospheric plasma spraying (APS). Their phase composition and microstructures were investigated comparatively. The thermal cycling and water vapor/oxygen corrosion behavior of these coating systems were compared at 1300 degrees C. The results showed that the thermal cycling life of the DCL-Yb3Al5O12 and TCL-Yb3Al5O12 EBC systems were 295 and 320 times, respectively. The failure of both the coating systems occurred between the Yb2Si2O7 layer and Si bond coat. The strength retention rate of DCL-Yb3Al5O12 and TCL-Yb3Al5O12 EBC systems after water vapor/oxygen corrosion for 70 h was 12.8% and 23.1%, respectively, and the fracture modes of both the systems exhibited "pseudoplastic" characteristic. TCL-Yb3Al5O12 EBC systems with a gradient structure of more layers exhibit more excellent high-temperature durability than DCL-Yb3Al5O12 EBCs.