Corrosion Behavior of Atmospheric Plasma-Sprayed YAG/8YSZ Double Ceramic-Layered Thermal Barrier Coatings in a Calcium-Magnesium-Alumino-Silicate Melt

Calcium-magnesium-alumino-silicate (CMAS) corrosion is one of the important causes of failure in thermal barrier coatings (TBCs). Herein, 8YSZ (8%Y2O3-ZrO2) single and YAG (Y3Al5O12)/8YSZ double ceramic-layered (DCL) TBCs were deposited on the Al2O3 substrate by atmospheric plasma spraying, respectively. The CMAS corrosion tests were conducted at 1250 degrees C for 1, 4, and 12 h, as well as on YAG/CMAS mixed powder (mass ratio 1:1) for 12 h. The microstructure and the corrosion products were analyzed to reveal the CMAS corrosion processes and mechanisms of these two types of TBCs. Results showed that YAG particle surface layer is slightly corroded by molten CMAS after 12 h at 1250 degrees C, which proved the good CMAS corrosion resistance and high-temperature stability of YAG. For the pure 8YSZ TBCs, the coating phase started to transfer from the as-sprayed tetrahedral phase to a monoclinic phase after corrosion for 1 h, and CMAS infiltrated the 8YSZ ceramic layer completely after 12 h. However, for the YAG/8YSZ DCL TBCs, only the high-melting-point apatite phase formed on the surface of TBCs blocked the further infiltration of CMAS by slowing further corrosion of CMAS. The protective apatite phase isolated CMAS from the internal YAG, keeping the bottom 8YSZ ceramic layer intact and extensively reducing the further damage to these TBCs.