Examination of the Thermal Stability of Plasma-Sprayed La₂Ce₂O₇/YSZ Composite Coating

LCO (La₂Ce₂O₇), a solid solution of La₂O₃ in CeO₂, is a promising top coating in TBCs. However, it is generally necessary to use LCO as a top coat on YSZ coating to construct a multilayer TBC due to poor mechanical properties of LCO. Therefore, the thermal and chemical stability of LCO/YSZ at high temperature environment become important issue. In this paper, the 50LCO-50YSZ composite coating was deposited using blend powders of YSZ and LCO. The LCO powders used have a nominal particle size range from 10 to 44μm. The LCO/YSZ deposits were exposed at 1300 ¢XC for different durations. The microstructure evolution at the LCO/YSZ interface was investigated by quasi-in-situ SEM and EDS examination. At an exposure temperature of 1300°C, it was observed that some LCO splats in contact with YSZ splats experienced the grain morphology change from columnar one to quasi-axial grains with interface healing and however some grains tended to disappear with thermal exposure. Results indicated that LCO-YSZ composite coating is not phase stable at 1300 °C. Diffusion of La element from LCO splat towards the adjacent YSZ splat occurred during sintering, leading to the formation of La₂Zr₂O₇ within YSZ splat.