Evolution of the void structure in plasma-sprayed YSZ deposits during heating

The evolution of the anisotropic void microstructure of plasma-sprayed yttria-stabilized zirconia (YSZ) deposits has been observed as a function of temperature by small-angle neutron scattering. Scattering experiments were carried out in-situ, in a furnace between 600 and 1400°C. The terminal slope (Porod scattering) of the scattering spectra was used to derive the specific surface area of the voids. For samples with sufficient scattering anisotropy, the two major void systems - intersplat (inter-lamellar) pores and intrasplat cracks - could be characterized separately. The pore and crack specific surface areas were found to depend on temperature differently. The specific surface area of the intrasplat cracks decreased markedly at temperatures below 1000°C, whereas the specific surface area of the intersplat pores began to decrease above 1000°C. This indicates important differences in the sintering of these two void systems probably related to their size and shape. Changes in the void surface were observed at temperatures as low as 800°C, a temperature comparable to, or less than, the usual operational temperature for this material.