Comparative investigation on the hot corrosion failure of YSZ and GdYb-YSZ double-ceramic-layer thermal barrier coatings under Na2SO4+V2O5 molten salts

The 5.2Gd2O3-5.6Yb2O3-9.5Y2O3 co-doped ZrO2 (GdYb-YSZ) double-ceramic-layer (DCL) thermal barrier coatings (TBCs) were prepared by atmospheric plasma spraying (APS) in this work. Hot corrosion behavior and failure mechanism of the APS GdYb-YSZ DCL and single-layer yttria partially stabilized zirconia (YSZ) TBCs under the Na2SO4+V2O5 molten salts were comparably investigated. The YSZ coating suffered from severe breakage after the hot corrosion test due to its poor corrosion resistance and easy infiltration by molten salts. In contrast, GdYb-YSZ DCL coating exhibited a better resistance to crack propagation and a significantly longer corrosion lifetime than the YSZ coating, which was attributed to the protective effect of the upper GdYb-YSZ layer. On the one hand, the superior phase stability of the GdYb-YSZ DCL coating could slow down the generation speed of phase transformation stress. On the other hand, the higher corrosion reaction rate of the upper GdYb-YSZ layer could suppress the further infiltration of molten salts into the inner TBCs, which improved the structural integrity of TBCs in corrosive environments.