The corrosion resistance of thermal barrier coatings against CMAS deposit at high temperature is significantly affected by the microstructure of the coatings. Enhancing the bonding ratio between splats can reduce the inter-connected pores and then obstructs the penetration of the molten CMAS into the coatings. In this study, atmospheric plasma sprayed ZrO 2 contains 8 wt. % Y 2 O 3 (8YSZ) coating with improved lamellar bonding ratios was deposited with full-molten droplets at an enhanced deposition temperature. The microstructure of the dense 8YSZ coating and conventional 8YSZ coating before and after thermal exposure with CMAS were characterized. It was clearly revealed that by adjusting the microstructure and designing a ceramic layer with high bonding ratio, the corrosion resistance of the thermal barrier coating could be enhanced. Moreover, by designing double-ceramic-layer (DCL) TBCs composed of a porous ceramic layer and well-bonded ceramic layer, the TBCs with high CMAS corrosion resistance and low thermal conductivity can be achieved.

The evaporation of both CeO 2 and La 2 O 3 in high temperature plasma arc leads to deviation of plasma sprayed La 2 Ce 2 O 7 coating composition from the starting powder particle. Such change results in significantly inhomogeneity of compositions within a coating which influences the performance of calcium-magnesium-alumina-silicate (CMAS) corrosion. In this study, the pellets with different Ce / La ratio were interacted with molten CMAS glass. The penetration of molten CMAS on different pellets was characterized by scanning electron microscopy and energy dispersive spectrum (EDS) and the phase of different powder mixtures treated at 1250 °C was characterized by X-ray diffraction ( XRD ). The effects of pellets with different Ce / La ratio on the CMAS corrosion after thermal exposure at 1250 °C for 50 h were investigated. The result demonstrated that pellets with ratio of Ce / La greater than or equal to 1.0 were completely dissolved into the molten CMAS, at the same time the others were also damaged, forming diffusion layer and reacted layer, respectively. The difference of the ratio of Ce / La indeed affected their performance against CMAS attack.

La 2 Ce 2 O 7 (LCO) is one of the promising candidates of high temperature thermal barrier coating materials. However, during plasma spraying, the evaporation of both CeO 2 and La 2 O 3 in high temperature plasma jet leads to deviation of coating composition from the starting powder particle. Such change results in significant inhomogeneity of compositions within a coating which influences the performance of resultant coating. In this study, an agglomerated La 2 Ce 2 O 7 powder with Ce / La ratio of 1.5 and in a size range of 5-60 μm was used to deposit the splats and coatings under different plasma spray conditions. The compositions of La 2 Ce 2 O 7 splats in different sizes were characterized by scanning electron microscopy and energy dispersive spectrum (EDS), and splat dimensions were characterized by 3D laser microscopy. The relationship between droplet size and splat composition was examined. Results showed that the Ce / La ratio in splats changes significantly with the splats diameter in a range from 1.5 to 0.7. There is a big difference in the composition of APS coatings deposited by coarse and fine powders. The mechanism causing splat composition change was examined based on the selective elemental loss during plasma heating of LCO particles in APS, aiming to control LCO coating composition.