Particle Size Effect on Gd₂O₃ Preferential Evaporation During Plasma Spraying of Gd₂Zr₂O₇

Rare-earth complex oxide ceramics are promising candidate materials for next-generation thermal barrier coatings due to their low thermal conductivity and phase stability. During plasma spraying, the component with a higher vapor pressure may experience severe preferential vaporization, resulting in significant composition change from the starting powder. In this study, Gd₂Zr₂O₇ (GZO) powder with a hollow spherical structure is used as the feedstock material to assess the vaporization behavior of G_d2O₃ during atmospheric plasma spraying (APS). Isolated Gd₂Zr₂O₇ splats with regular disc shapes in different sizes were deposited on stainless steel substrates at a deposition temperature of 300 °C to study the effects of particle size on vaporization loss. The elemental composition of each splat was analyzed by EDS, and the ratio of Gd to Zr in different splats with different diameters was obtained. The results show that the vaporization loss of Gd increases markedly with decreasing particle size due to the preferential vaporization of G_d2O₃. Using Gd₂Zr₂O₇ powders of a certain size can reduce Gd loss, although the effect is determined by molten droplet size rather than apparent powder particle size.