Calcia-magnesia-alumino-silicate-induced degradation of (Gd_0.9Yb_0.1)₂Zr₂O₇ thermal barrier coatings prepared by plasma spray-physical vapor deposition (PS-PVD)

(Gd_0.9Yb_0.1)₂Zr₂O₇ (GYbZ) coatings with quasi-columnar structure prepared by PS-PVD were isothermally exposed to Calcia-magnesia-alumino-silicate (CMAS) at T = 1300 °C for t₀ = 0.1 h, t₁ = 1 h, t₂ = 10 h, and t₃ = 100 h. The resistance of GYbZ coatings against the CMAS melt penetration was investigated by wetting test and the reaction products were analyzed by energy-dispersive X-ray spectroscopy (EDS). The results show that a dense reaction layer was formed after isothermal exposure for t₁ = 1 h, and the thickness of the reaction layers was almost the same from t₁ = 1 h to t₃ = 100 h, which indicated that the penetration of CMAS was basically suppressed. The particles between columns played a significant role in the rapid generation of a large amount of CMAS barrier apatite layer which prevented the penetration of the CMAS melt in the axial direction. The main reaction products were Gd-apatite, fluorite and spinel of which the Gd-apatite slowly grew from “free-island” to “net-frame”.