Oxidation Behavior of Single-Layer Gd2Zr2O7, and Gd2Zr2O7/YbSZ, and Double-Layer YSZ + Gd2Zr2O7/YbSZ Thermal Barrier Coatings

Oxidation is one of the failure mechanisms of gas turbines under operating temperature. Yttria-stabilized zirconia (YSZ) is well-known ceramic topcoat material of thermal barrier coatings (TBCs), but it has some drawbacks. From this point of view, other new materials such as rare earth zirconate are interesting. In the present research, single-layer Gd2Zr2O7 (GZO), and GZO/YbSZ (Gd2Zr2O7 + 50 wt% YbSZ), and double-layer YSZ + GZO/YbSZ (YSZ/Gd2Zr2O7 + 50 wt% YbSZ) topcoats as TBC were deposited by air plasma spraying. To estimate the phase stability of homogeneous mixtures of GZO (pyrochlore) and YbSZ (tetragonal), heat treatment was conducted at 1400 °C and showed complete conversion to a single-cubic (fluorite) phase after 100 h. The as-sprayed TBCs were subjected to oxidation for different times at 900 °C, and their features were investigated by different analysis techniques (SEM and XRD). The microstructural analysis indicated that the thickness of the thermally grown oxide layer was less for GZO coating due to reduced oxygen diffusion. Conversely, because of the lower fracture toughness and lower thermal expansion of GZO, it had a considerably less lifetime. It was concluded that coatings with the new composition GZO/YbSZ exhibited higher oxidation resistance and longer lifetime than GZO coatings.