Influence of Process Parameters on the Microstructural and Mechanical Properties of Plasma Sprayed Nanostructured YSZ Coatings

Plasma sprayed ceramic coatings can be used for thermal protection of hot-section metal components of turbine engines, in order to improve their durability and efficiency. The presence of nanostructures, deriving from partial melting of agglomerated nanostructured particles, represents an interesting technological solution in order to improve their functional characteristics. In this work nanostructured yttria stabilized zirconia (YSZ) coatings were deposited by plasma spraying. The influence of the main process parameters on their microstructural and mechanical properties was investigated by scanning electron microscopy (SEM) and indentation techniques at micro- and nano-scale. Their porous microstructure was composed of well melted overlapped splats and partially melted nanostructured areas. This bimodal microstructure led to a bimodal distribution of the mechanical properties. An increase of plasma power and spraying distance was able to produce denser coatings, with lower content of embedded nanostructures, which exhibited higher elastic modulus and hardness. With increasing the indentation load the mechanical properties decreased, due to the influence of microstructural defects.