Microstructure and property evolution of Gd3NbO7-GdNbO4 composite thermal barrier coating

To fulfill the multi-functional requirements of advanced thermal barrier coatings , composite oxides are emerging as promising candidates due to their enhanced thermal and mechanical properties. Although numerous composite materials have been developed, a comprehensive investigation of their microstructure and property evolution is still lacking. In this study, we conducted a comprehensive investigation of the microstructure and property evolution of the Gd 3 NbO 7 -GdNbO 4 composite thermal barrier coating as a case study. The as-sprayed Gd 3 NbO 7 -GdNbO 4 coating was verified to possess a single fluorite phase with a composition of Nb x Gd (1-x) O (1.5+x) , which is a metastable phase. After heat treatment, the monoclinic GdNbO 4 phase precipitated without altering the coating microstructure. During high-temperature thermal exposure, rapid sintering occurred, accompanied by grain coarsening and pore healing, leading to an increase in hardness and toughness. The toughness of the Gd 3 NbO 7 -GdNbO 4 coating was higher than that of rare earth zirconates due to the presence of multiple toughening mechanisms. Additionally, a low thermal conductivity of 1.33 W/(m·K) was achieved for the Gd 3 NbO 7 -GdNbO 4 coating due to rapid sintering. Notably, there were no abrupt changes in the CTE curves during the heating process, which is crucial for thermal barrier coatings. The CTE reaches 11.0×10 −6 K −1 at 1300 °C, which is close to YSZ, indicating that the Gd 3 NbO 7 -GdNbO 4 coating is suitable for advanced thermal barrier coatings.