Corrosion behavior of calcium-magnesium-alumino-silicate on (La,Gd)₂Zr₂O₇/YSZ multilayer for thermal barrier coatings

Abstract

In this study, the high-temperature corrosion behavior was evaluated for (La,Gd)₂Zr₂O₇ (LGZ) used as a promising thermal barrier coatings (TBCs) material. (La,Gd)₂Zr₂O₇ + YSZ multilayer prepared from atmospheric plasma spray (APS) were exposed to calcium-magnesium-alumino-silicate (CMAS) melt at 1300 °C for 2, 12, 48, and 100 h. Molten CMAS and (La,Gd)₂Zr₂O₇ reacted to form reaction layer Ca₂Gd₈(SiO₄)₆O₂ (apatite) at 1300 °C. The thickness of the reaction layer increased with increasing heat-treatment time. A correlation between the hardness and Young’s modulus relationship for the reaction layer of the coating was observed for the microstructure using nanoindentation. It was confirmed that the pores of the coating were reduced through the infiltration of molten CMAS in the initial stage of the corrosion reaction, and the hardness and Young’s modulus were increased due to densification. Fracture toughness increased with heat treatment time in both directions (in-plane and through-thickness). The fracture toughness in the in-plane direction is 0.19–0.23 MPa√m. On the other hand, the fracture resistance in the thickness direction was 0.87–1.26 MPa√m, which was higher than that in the in-plane direction. These results show that the crack propagates in the in-plane direction and causes TBC delamination.