Mechanical property variations within thermal barrier coatings

Abstract

The mechanical properties of nanostructured yttria stabilized zirconia (YSZ) coatings were investigated using an instrumented indentation technique. Coatings were produced using the Triple-Torch Plasma Reactor (TTPR) where three plasma jet plumes converge to form a single jet where powder is injected axially. Partially fused clusters of sub-micron particles are characteristic for the coating microstructure. Flattened particles, termed as splats that are typical for conventional YSZ coatings were not observed.

The microstructure exhibits a low isotropy that is related to variations in mechanical properties that are measured in directions parallel (normal to the coating plane) and perpendicular to the spray direction (in the plane of the coating). The microstructure of the nanostructured coating, which is different from a conventional coating, has a significant effect on the anisotropy of the mechanical properties. The in-plane elastic modulus of the nanostructured coating is lower than the normal modulus, as opposed to a conventional YSZ coating where the ratio is inversed. Multiple indentations arranged in arrays were used to map the variation in mechanical properties. Indentation results obtained using spherical and Vickers indenters are compared.