Microstructural characterization of plasma-sprayed nanostructured zirconia powders and coatings

The objective of this paper was to study the melting state of nanoscale zirconia powders in plasma jet, examine the crystalline phase and microstructural characterization of the plasma sprayed nanostructured zirconia powders and coatings. The cross-section morphology of water-quenched powders revealed that most of the starting powders were molten in the plasma jet. Phase analysis using XRD spectra proved that the monoclinic phase zirconia of the starting powders transferred into tetragonal phase zirconia after the plasma spraying. SEM analysis indicated that the as-sprayed coatings exhibited lamellar structure, about 0.5–5 μm in thickness of a single lamella, which was found to be a characteristic feature of the plasma-sprayed nanostructured zirconia coating. Inside of the lamellae, columnar grains were observed. The mean grain size of the as-sprayed zirconia coating is about 80 nm.