Laser glazing of plasma-sprayed nanostructured yttria stabilized zirconia thermal barrier coatings

Nanostructured thermal barrier coatings (TBCs) consisting of yttria stabilized zirconia (YSZ) ceramic top coat and NiCrAlY metallic bond coat were prepared by atmospheric plasma spraying (APS). The Nd:YAG pulsed laser was used for laser treatment of top coat surface. The microstructure and thermal insulation capability of plasma-sprayed and laser-glazed thermal barrier coatings were investigated. The microstructure and phase composition of the coating were characterized by field emission scanning electron microscopy (FESEM) and X-ray diffractometry (XRD). The nanostructured plasma-sprayed coating contained non-melted or partially melted nanosized particles and columnar grains, whereas the microstructure of laser-glazed coating consisted of columnar grains in the fracture surface and equiaxed grains on the surface. Laser glazing, which helps to eliminate the surface porosities and other structural defects of coatings deposited by the plasma spraying method, should contribute to the improvement of their surface roughness. XRD results revealed that both as-sprayed and laser-glazed coatings consisted of non-transformable tetragonal (T′) phase. The results of the thermal insulation capability test indicated that the thermal insulation capability of the laser-glazed coating, as compared to the as-sprayed coating, was slightly lower due to the microstructural change in the glazed layer of top coat.