Axial Plasma Spraying of Solution Precursors: Adding a New Dimension to Future TBC Development?

Thermal barrier coatings (TBC) are an essential part of modern gas turbines for aviation and power generation. As such, there is an incessant demand for improved TBC performance and longevity. Of the possible coating microstructures, the columnar structure first produced by electron beam physical vapor deposition was found to be most durable. The subsequently developed suspension plasma spray coatings are seen as an alternative method for producing columnar TBC’s but require flammable solvents to achieve such structures. Aqueous solution precursors have also been utilized as a feedstock to deposit TBCs; however, columnar structures have proven elusive, with deposition conditions and throughputs with radial feed spray torches also being industrially unattractive. The first columnar coatings from an aqueous solution precursor using an axial feed capable plasma torch will be presented. Coatings have been shown to be columnar structured over a robust operating window, fully tetragonal in phase constitution and capable of being deposited at rates that can be commercially interesting. The evolution of the columnar structure has also been experimentally visualized. These initial results lay a good foundation for further TBC development utilizing an aqueous, powder-free, feedstock.