Thermal Properties and Durability of a Rare-Earth-Doped YSZ Bilayer Coating System

To protect gas turbine hot section components from operating temperatures exceeding 1100 ℃, thermal barrier coating systems are used. Although yttria-stabilized zirconia (YSZ) is commercially used as a thermal barrier coating material, it is destabilized by phase transformations when exposed to extremely high-temperature operating environments (>1200 ℃). In efforts to resolve this critical issue, Gd2O3- and Yb2O3-doped YSZ species have been developed as candidate alternative materials. Compared with conventional YSZ, however, GdYb-YSZ exhibits reduced thermal cycling resistance performance under 1400 ℃ thermal cycling test conditions. To overcome this drawback, a bilayer TBC structure was designed and prepared using conventional YSZ and rare-earth-oxide-modified GdYb-YSZ in the current study. The thermal conductivity and high-temperature thermal cycling durability were subsequently evaluated for bilayer coatings with various thickness ratios of YSZ (bottom layer) and GdYb-YSZ (top layer). Additionally, YSZ derivatives respectively doped with Sc2O3, Gd2O3, Dy2O3, and TiO2 (developed in our previous research) were prepared in both single-layer and bilayer structures and the thermal conductivity and thermal cycling durability were compared for both structures. All bilayerstructured TBC samples respectively exhibited lower thermal conductivity than the single-layer YSZ baseline value of 1.1 W/(m·K). Moreover, in high-temperature thermal cycling durability assessments, the bilayer structures exhibited equivalent or superior durability compared with the single-layer YSZ coating. These findings highlight the potential of these materials for use as advanced TBC materials in gas turbines.