Axial plasma spraying of aqueous solution precursors: A facile approach for columnar thermal barrier coatings

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 vapour deposition was found to be most durable. The subsequently developed suspension plasma spray coatings are seen as an alternative method for producing columnar TBCs but typically utilise flammable solvents to achieve such structures. Aqueous solution precursors have also been used as a feedstock to deposit yttria stabilised zirconia (YSZ) TBCs; however, columnar structures have proven elusive, with solution precursor plasma spray (SPPS) deposition conditions and throughputs involving radial feed spray torches also being industrially unattractive. This study illustrates the first columnar coatings of single-layer yttria stabilised zirconia from an aqueous solution precursor using an axial feed capable plasma torch. 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. These initial results lay a great foundation for further TBC development utilizing an aqueous, powder-free, feedstock.