Hot-Corrosion Behavior of Gd₂O₃–Yb₂O₃ Co-Doped YSZ Thermal Barrier Coatings in the Presence of V₂O₅ Molten Salt

In this study, thermal barrier coatings (TBC) consisting of 3.5 mol% Yb₂O₃-stabilized ZrO₂ co-doped with 1 mol% Gd₂O₃ and 1 mol% Yb₂O₃ (referred to as GdYb-YSZ) were fabricated by means of air plasma spraying. The as-fabricated coatings exhibited a metastable tetragonal (t′) structure. The hot-corrosion behavior of the GdYb–YSZ TBCs was investigated at 700, 800, 900, and 1000 °C for 10 h in the presence of V₂O₅ molten salt. During the corrosion tests, the t′ phase transformed into a monoclinic (m) phase; nevertheless, it was still detected on the corroded surfaces. The amount of t′ phase decreased with increasing corrosion temperature. The corrosion products formed on the GdYb-YSZ TBCs in V₂O₅ comprised Yb, Gd-doped YVO₄, and m-ZrO₂, irrespective of the temperature of corrosion. However, higher temperatures changed the morphologies of the Yb- and Gd-doped YVO₄ corrosion products. The GdYb–YSZ TBCs exhibited improved corrosion resistance to V₂O₅ molten salt when compared to YSZ TBCs, and the related mechanism is discussed in detail in this paper.