Air Plasma-Sprayed Yttria and Yttria-Stabilized Zirconia Thermal Barrier Coatings Subjected to Calcium-Magnesium-Alumino-Silicate (CMAS)

Yttria (Y 2 O 3 ) and zirconia (ZrO 2 ) stabilized by 8 and 20 wt.%Y 2 O 3 thermal barrier coatings (TBCs) subjected to calcium-magnesium-alumino-silicate (CMAS) have been investigated. Free-standing Y 2 O 3 , 8 and 20 wt.%YSZ coatings covered with synthetic CMAS slurry were heated at 1300 °C in air for 24 h in order to assess the effect of Y 2 O 3 on the corrosion resistance of the coatings subjected to CMAS. The microstructures and phase compositions of the coatings were characterized by SEM, EDS, XRD, RS, and TEM. TBCs with higher Y 2 O 3 content exhibited better CMAS corrosion resistance. Phase transformation of ZrO 2 from tetragonal (t) to monoclinic (m) occurred during the interaction of 8YSZ TBCs and CMAS, due to the depletion of Y 2 O 3 in the coating. Some amounts of original c -ZrO 2 still survived in 20YSZ TBCs along with a small amount of m -ZrO 2 that appeared after reaction with CMAS. Furthermore, Y 2 O 3 coating was found to be particularly highly effective in resisting the penetration of molten CMAS glass at high temperature (1300 °C). This may be ascribed to the formation of sealing layers composed of Y-apatite phase [based on Ca 4 Y 6 (SiO 4 ) 6 O and Y 4.67 (SiO 4 ) 3 O] by the high-temperature chemical interactions of Y 2 O 3 coating and CMAS glass.