Microstructural properties and high temperature performance of plasma sprayed YSZ thermal barrier coatings from nanostructured powders

The improvements of performances of turbojets in terms of thrust and reliability are strongly affected by the design of the turbine hi-pressure stages, and in particular by the maximum gas temperature at inlet. In order to increase the working temperatures and to extend the time between inspection and/or substitution of the relevant components, the research must be focussed on materials with high thermo-mechanical properties. The principal requirement for ceramic TBC being the resistance to repeated thermal cycles during operation while assuring the protection of substrate against heat, fragile behaviour of traditional ceramics is a critical issue [1-3]. One of the possible solutions to the aforementioned problem can be the adoption of nanostructured materials, that at least theoretically provide higher fracture thoughness and thermal shock resistance than traditional ones. As thermal spraying is the most efficient and economical deposition technique for thermal barrier coatings [4-5], it appears sensible to investigate the possibility of using it for the fabrication of nanostructured thermal barrier coatings, due to the very short residence time of starting materials at high temperature. A careful selection of process parameters is necessary for preventing the shortcomings correlated to the risk of grain coarsening and phase changing [6-7]. In the present communication, preliminary results concerning the characterization of zirconia-yttria APS nanostructured coatings (obtained by deposition of commercially available nanostructured powders) as well as a comparison with the performances of conventional microstructured coatings are presented.