New functionally graded thermal barrier coating system based on LaMgAl11O19/YSZ prepared by air plasma spraying

A new functionally graded thermal barrier coating (FG-TBC) based on LaMgAl11O19 (LaMA)/YSZ has been designed and prepared via air plasma spraying. The microstructure and phase stability are investigated by X-ray diffraction, SEM and high-temperature DSC analysis. Results indicate that all the LaMA and LaMA-containing intermediate composite coatings suffer irreversible phase transformations induced by the recrystallization of amorphous LaMA coating and γ to α-Al2O3 transition during heating, and LaMA and YSZ coatings are chemically compatible at elevated temperature. The appearances of LaMA platelet-like grains during the recrystallization process, impart the intermediate LaMA-containing composite coating layers with improved sintering resistance, reduced densities and hardness. The wear behavior and the influences of heat treatments on the microhardness of the coatings are also investigated. Coefficient of thermal expansion changes gradually from the YSZ bottom layer to the LaMA top layer, which would result in a reduced residual stress level compared to the LaMA/YSZ double ceramic layered TBC system. Such a FG-TBC displays an excellent burner-rig thermal cycling lifetime of ~ 11,749 cycles at the surface testing temperature about 1372 °C, showing the great potential for advanced TBCs applications in the future.