Influence of Elemental Evaporation on the Composition of La₂Ce₂O₇ Splats Deposited by Plasma Spraying

La₂Ce₂O₇ (LCO) is one of the promising candidates of high temperature thermal barrier coating materials. However, during plasma spraying, the evaporation of both CeO₂ and La₂O₃ 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 La₂Ce₂O₇ 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 La₂Ce₂O₇ 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.