Abstract
Gradient thermal barrier coatings (GTBCs) have been produced by electron beam physical vapor deposition (EB-PVD). Their performance was evaluated by isothermal oxidation and cyclic high-temperature hot-corrosion tests. It is found that the GTBCs exhibited better resistance to high-temperature oxidation and cyclic high-temperature hot-corrosion (HTHC) than traditional two-layered TBCs. A dense Al2O3 layer on the bond coat of GTBCs can effectively prohibit inward diffusion of oxidants such as O and S and outward diffusion of Al and Cr. On the other hand, an “inlaid” interface, the formation of which resulted from the oxidation of Al diffusion into the gaps between the columns of bond coat during the fabrication of the GTBCs, contributes to reinforce the adherence of the Al2O3 layer to the bond coat. During fluxing of the Al2O3 layer, S and O diffused into the bond coat. Cracks developed in the surface layer of bond coat by the combined effect of sulfidation of the bond coat and thermal cycling, and finally led to failure of the GTBC.
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