Challenges for Plasma Spray Deposition of Decomposition-Prone Perovskite Coatings

Processing of powder feedstock materials often influences the deposition behavior and ultimately, the properties of the atmospheric plasma spray (APS) deposited coatings. The necessity of materials design and the control of deposition parameters are therefore, of high importance. Feedstock from promising ceramic thermal barrier coating materials with Ba(Mg_1/3Ta_2/3)O₃ and La(Al_1/4Mg_1/2T_1/4)O₃ perovskite structures (λ~ 2 W/m-K and α~11x10-6 /K at 1473 K) were prepared through solid state and conventional spray drying techniques. The powders were then deposited on metallic substrates by APS process. Monitoring of in-flight particle characteristics and splat formation as well as characterization of deposited coatings, were conducted. It was found that these types of perovskite materials tend to lose constituents during deposition by atmospheric plasma spraying. This paper reports on the challenges of powder feedstock design and the control of critical deposition parameters to prevent or minimize the non-stoichiometric deposition of decomposition-prone perovskite coatings by APS process.