Microstructural characterization of modified YSZ thermal barrier coatings by high-current pulsed electron beam

Thermal sprayed YSZ coatings subjected to high-current pulsed electron beam (HCPEB) with different pulses were investigated. The microstructure evolution, surface roughness and phase transformation of the coatings were characterized by means of a scanning electron microscope (SEM), a three-dimensional laser scanning microscope (LSM) and X-ray diffraction (XRD), respectively. Under HCPEB irradiation, the coarse surface was melted and a flat and compact surface with a continuous micro-crack network was formed. At the same time, rapid thermal cycles during HCPEB irradiation led to the very fine grains formed on the surface and the fully dense columnar grains in the fracture cross-section. When using 10 or 20 pulses, wavy morphology and vapor deposition were induced due to the evaporation effect. The phase composition in irradiated coatings mainly consisted of a non-equilibrium t′-phase, the same as the as-sprayed phase composition. After HCPEB irradiation with 10 or 20 pulses, the residual m-phase was mostly eliminated owing to the homogenization of composition during the HCPEB irradiated process. High temperature oxidation test indicates that the irradiated coating with 10 pulses has a much higher oxidation resistance.