Effect of diffusion barrier on the high-temperature oxidation behavior of thermal barrier coatings

A selective oxidation technique has been applied to form a diffusion barrier on the Ni-based superalloy substrate by heating the substrate with electron beam of the electron beam-physical vapor deposition (EB-PVD) facility. The interdiffusion behavior, cross-sectional morphology, isothermal and cyclic oxidations were studied for thermal barrier coatings (TBCs) with and without diffusion barrier. Under an oxygen partial pressure of about 2.5 × 10−5 kPa and after heating for 30 min, the alloying elements of substrate were selectively oxidized and a thin layer of diffusion barrier with a thickness of 500 nm was formed on the substrate, and the diffusion barrier was composed of mainly α-Al2O3, NiO and Cr2O3. Different alloying elements had different diffusion behaviors, it was observed that Al and Cr diffused inwards from the bond coat to the substrate, and Ti, Mo and W diffused outwards from the substrate to the bond coat. It was also observed that the lifetime of TBC with diffusion barrier could be partially improved, though the experimental results received from isothermal oxidation and cyclic tests are not extremely obvious.