Fabrication and Evaluation of Plasma-Sprayed Nanostructured and Conventional YSZ Thermal Barrier Coatings

Yttria stabilized zirconia (YSZ) nanostructured and conventional coatings have been prepared by atmospheric plasma spraying (APS) on NiCoCrAlY-coated superalloy substrates. Bonding strength test was carried out based on the ASTM-C-633-01. To evaluate thermal insulation value of coatings, the thermal insulation capability test was designed and administered. Field emission scanning electron microscope (FESEM) and X-ray diffractometry (XRD) were employed to characterize the microstructures and the phase compositions of the powders and coatings. Nanostructured YSZ coating exhibited a bimodal microstructure consisting of nanosized particles retained from the powder and microcolumnar grains formed through the resolidification of the molten part of powder, whereas the microstructure of conventional YSZ coating consisted of columnar-grain splats. Both nanostructured and conventional YSZ coatings consisted of the non-transformable tetragonal phase. The results revealed that nanostructured coating, due to unique microstructure container of nanozones, presented improved bonding strength and thermal insulation capability as compared to the conventional coating.