Quantification of void networks of as-sprayed and annealed nanostructured yttria-stabilized zirconia (YSZ) deposits manufactured by suspension plasma spraying

Suspension plasma spraying (SPS) allows processing a stabilized suspension of nanometer-sized feedstock particles to form thick (from 20 to 100 μm, average values) deposits.The void content and porous network of such deposits are difficult to quantify (in terms of void and size distributions, anisotropy, etc.) using conventional techniques due to their low resolution. The combination of ultra-small-angle X-ray scattering (USAXS) and helium pycnometry permits to address some of the characteristics of this void network.Deposits of yttria-partially stabilized zirconia (YSZ) were manufactured by plasma spraying a suspension made of solid sub-micrometer-sized particles (50 and 400 nm) with several sets of spray operating parameters. Results indicate that the average void size exhibits the same scale as the solid structure; i.e., nanometer sizes and multimodal size distribution which varies with spray operating parameters. About 90% of voids (by number) exhibit characteristic dimensions smaller than 40 nm. The cumulative void volume fraction of such as-sprayed deposits varies between about 13 and 20%, depending upon operating parameters. The void network architecture evolves also with annealing conditions: the void size distribution evolves toward higher void characteristic dimensions as a result of sintering of smallest voids but the cumulative void content does not decrease significantly.