Compositional control and high-temperature phase stability of plasma-sprayed Ba(Mg_1/3Ta_2/3)O₃ coatings

The Ba(Mg_1/3Ta_2/3)O₃ (BMT) ceramic is considered a promising material for high-performance thermal barrier coating (TBC), due to the ultra-high melting point and excellent thermophysical properties. However, the preferential evaporation of Mg from BMT during plasma spraying causes the composition in deposited coatings to deviate from the standard stoichiometry, resulting in the formation of undesirable barium tantalite. These impurities would accelerate the cracking and failure of BMT with low fracture toughness during thermal shock, which greatly limits the application of BMT coatings. In this study, the evaporation of Mg, and the evolutionary characteristics of the composition and microstructure of BMT particle in the plasma spray process were investigated. The relationship between the melting conditions of BMT particles and the composition and microstructure of the coatings was analyzed. The compositional controls, and the high-temperature phase stability of plasma-sprayed BMT coatings were studied and characterized. The results indicate that the evaporation intensity of Mg was strongly affected by the melting conditions of the BMT particles in the plasma jet. The particles with a higher degree of melting had a greater evaporation intensity of Mg, owing to the higher heat transfer and element diffusion rate, and more impurity phases formed in the deposited coating. The nonuniformity of Mg evaporation in BMT particle could lead to composition segregation, promoting the formation of the impurity phases during particle solidification, and ultimately affect the composition uniformity of the coating. By employing the powder with large particle sizes and adjusting the spray parameters to reduce the energy of plasma jet under the premise of ensuring the coating deposition quality, the evaporation intensity of Mg and the content of impurity phase could be significantly restrained, and the high-temperature phase stability of the coatings could be greatly improved compared to the original unmodified BMT coatings.