Calcium-Magnesium-Aluminum-Silicate (CMAS) Corrosion Resistance of Y-Yb-Gd-Stabilized Zirconia Thermal Barrier Coatings

It was published that zirconate coatings containing Gd/Yb and yttria-stabilized zirconia (YSZ) coatings with high Y content had good calcium-magnesium-aluminum-silicate (CMAS) corrosion resistance. However, there are few reports on CMAS resistance of zirconia-based thermal barrier coatings (TBCs) doped with Y, Gd and Yb. This article intends to explore the role of Y, Gd and Yb in resisting CMAS corrosion of zirconia-based TBCs. The purpose is to optimize the rare earth modification of zirconia-based TBCs. 8YSZ and ZrO2-9.5Y2O3-5.6Yb2O3-5.2Gd2O3 free-standing TBCs were produced by air plasma spraying (APS) with commercial powders. The CMAS corrosion behavior and failure mechanism of these coatings were studied by heat treatment at 1350 °C. The microstructure and composition were characterized. The results showed the CMAS deposited on the surface of 8YSZ/YSZ-Yb-Gd coatings gradually penetrated into coatings. ZrSiO4 and m-ZrO2 were observed in the shallow layer of coatings. The diffusion rate of Y3+ in coatings into CMAS was greater than that of Gd3+ and Yb3+. Compared with YSZ coatings, CMAS penetrated deeper in YSZ-Yb-Gd coatings after the same corrosion time. The spallation of YSZ-Yb-Gd coatings occurred earlier than 8YSZ. In general, adding a small amount of Yb and Gd did not improve the CMAS resistance of YSZ TBCs.