Particle size effect on Gd2O3 preferential evaporation during plasma spraying of Gd2Zr2O7

Rare earth complex oxides are considered as promising condidate materiala for next generation thermal barrier coatings. During plasma spraying, the component with a higher vapor pressure may experience severe preferential vaporization to result in signicant composition change than starting powder. In this study, Gd₂Zr₂O₇ is used as typical material in a wide range of particle size to examine the vaporization behavior of Gd₂O₃ during atmospheric plasma spraying. Isolated Gd₂Zr₂O₇ splats with regular disc shape in different sizes were deposited on polished stainless steel substrates at ~300 ℃ to study the effects of particle sizes on vaporation loss of Gd₂O₃. The elemental compositions of each splat were analyzed by EDS. The results show that the vaporation loss of Gd increases remarkably with the decrease of particle size. The size effect was correlated to the distribution of Gd in the deposited coating. It is clear that there exists evident size effect of Gd loss resulting from preferential vaporization of Gd₂O₃ and using Gd₂Zr₂O₇ powders with certain larger size the Gd loss can be significantly reduced. Thus, it is confirmed that a Gd₂Zr₂O₇ coating with more homogeneous compositions can be deposited by plasma spraying using larger sized powders.