Development and implementation of plasma sprayed nanostructured ceramic coatings

A broad overview of the science and technology leading to the development and implementation of the first plasma sprayed nanostructured coating is described in this paper. Nanostructured alumina and titania powders were blended and reconstituted to a sprayable size. Thermal spray process diagnostics, modeling and Taguchi design of experiments were used to define the optimum plasma spray conditions to produce nanostructured alumina–titania coatings. It was found that the microstructure and properties of these coatings could be related to a critical process spray parameter (CPSP), defined as the gun power divided by the primary gas flow rate. Optimum properties were determined at intermediate values of CPSP. These conditions produce limited melting of the powder and retained nanostructure in the coatings. A broad range of mechanical properties of the nanostructured alumina–titania coatings was evaluated and compared to the Metco 130 commercial baseline. It was found that the nanostructured alumina–titania coatings exhibited superior wear resistance, adhesion, toughness and spallation resistance. The technology for plasma spraying these nanostructured coatings was transferred to the US Navy and one of their approved coating suppliers. They confirmed the superior properties of the nanostructured alumina–titania coatings and qualified them for use in a number of shipboard and submarine applications.