Thermal cycling of EB-PVD TBCs based on YSZ ceramic coat and diffusion aluminide bond coat

Abstract

The objective of this research was to optimize the surface morphology and element compositional distribution of the bond coat by adjusting the hydrogen flow, and to fabricate the 6–8 wt% yttria partially stabilized zirconia (YSZ) ceramic topcoat via EB-PVD. The interfacial stability and spalling failure behavior of thermal barrier coatings (TBCs) were evaluated by cyclic oxidation test at 1373 K. The results show that with the increment of hydrogen flow, the X-ray diffraction peak belonging to the β phase tends to be obvious and the high temperature oxidation resistance becomes correspondingly excellent. There are no microcracks, spalling, peeling, edge warping and cloud spatter on the ceramic coating surface. The cross section of the ceramic layer exhibits a typical columnar grain microstructure. The columnar crystal grows evenly perpendicular to the interface between the ceramic and bonding layers. Although it has been exposed to long-term thermal exposure, the ceramic coat has densified and sintered locally, and the grain boundary between the columnar grains is basically disappeared, the ceramic coat surface still has the typical columnar crystal “cauliflower” shape. Lots of transverse cracks and voids have been found at the interface of the bond coat and TGO layer, and within a dozen micrometers approach the bond coat surface. Internal fracture has occurred in the bonding layer and bridging structures have been developed due to internal oxidation in the bond coat.