Thermal stability of plasma-sprayed La2Ce2O7/YSZ composite coating

A composite coating composed of La2Ce2O2 (LCO) and yttria-stabilized zirconia (YSZ) in a weight ratio of 1:1 was deposited by the plasma spraying using a blended YSZ and LCO powders, and the stability of the LCO/YSZ interface exposed to a high temperature was investigated. The LCO/YSZ deposits were exposed at 1300 °C for different durations. The microstructure evolution at the LCO/YSZ interface was investigated by quasi-in-situ scanning electron microscopy assisted by X-ray energy-dispersive spectrum analyses and X-ray diffraction measurements. At an exposure temperature of 1300 °C, the grain morphology of LCO splats in contact with YSZ splats changed from columnar grains to quasi-axial grains with interface healing, and some grains tended to disappear during the thermal exposure. The results indicate that the phases in LCO-YSZ composite coating are not stable at 1300 °C. The element La in the LCO splat diffused towards the adjacent YSZ splat during the exposure, generating the reaction product layers composed of La2Zr2O7 between the LCO and YSZ splats. After exposed for 200 h, the composite coating consisted of a mixture of mainly La2Zr2O7 and CeO2 and a minor amount of YSZ, accounting for the unusual decrease in the thermal conductivity at the late stage of exposure.