Failure Mechanism of Yb₂O₃-Gd₂O₃-Y₂O₃ Co-Dopzed Zirconia Double Ceramic Thermal Barrier Coating in Na₂SO₄+V₂O₅ Environment

A double ceramic (GYYZ/YSZ) thermal barrier (TBCs) coating with 9.5Y₂O₃-Y₂O₃-5.6Yb₂O₃-5.2Gd₂O₃ co-doped ZrO₂ (GYYZ) as outer layer and Y₂O₃ stabilized ZrO₂ (YSZ) as inner layer were prepared by atmospheric plasma spraying (APS) method, and compared to the traditional single-layer YSZ TBCs. Thermal cycling tests were conducted to investigate hot corrosion behavior and failure mechanism of the two coatings in the Na₂SO₄+V₂O₅ environment. The results show that compared with YSZ, GYYZ exhibitted stronger reactivity in corrosive environment due to its higher mass fraction of metal oxide stabilizers. The Gd₂O₃ and Y₂O₃ in GYYZ coating had strong Lewis basicity, which would preferentially participate in the reaction. The inactive Yb₂O₃ would be left behind to be the stabilizer of ZrO₂, which was beneficial to maintain the phase stability of GYYZ/YSZ coating in the corrosive environment. Since GYYZ coating underwent less transformation from t′-ZrO₂ phase to m-ZrO₂ phase in the corrosion environment, the internal accumulated phase transition stress was smaller, so GYYZ/YSZ coating exhibited stronger resistance to crack propagation, and its thermal cycle corrosion life was significantly higher than that of YSZ coating.