Preparation of Ba(Mg_1/3Ta_2/3)O₃ Suspension and the Coating Microstructure Based on Suspension Plasma Spraying

[Purposes] The strain tolerance of Ba(Mg_1/3Ta_2/3)O₃ (BMT) thermal barrier coating prepared by conventional atmospheric plasma spraying is low. [Methods] With suspension lasma spraying (SPS), BMT suspensions with different compositions are prepared by mechanical ball grinding with ethanol as the dispersion medium and polyacrylic acid (PAA), polyethyleneimine (PEI), and polyethylene glycol (PEG) as dispersants. The dispersion behavior of BMT suspension was studied through gravity sedimentation observation method, UV-Vis spectrophotometry, and Zeta potentiometry. The effects of dispersant type and content on the stability of BMT suspension were analyzed. The BMT coating was deposited by SPS, and the phase structure, surface morphology, and cross-section microstructure of the BMT coating were characterized and analyzed. [Findings] The results show that the adsorption of the dispersant PEI on the surface of the BMT particles improves their Zeta potential, enhances the repulsive force between particles, and provides a steric hindrance, which results the better dispersion of BMT suspension with PEI dispersant than that with PAA and PEG. In addition, the BMT suspension with PEI has a low viscosity (1.5-2 mPa·s), making it appropriate for SPS. The coating prepared by SPS essentially preserves the BMT phase structure, and shows a clear columnar-crystal microstructure. With the increases of the solid content in the suspension, the deposition efficiency of the BMT coating increase, and the volume of columnar crystals formed becomes larger, which conforms to the microstructural characteristics of high strain tolerance coatings.