The oxidation behavior of TiAlNb intermetallics with coatings at 800 °C

The discontinuous and cyclic oxidation behavior of TiAlNb intermetallics with coatings such as NiCrAlY, TiAlCr and ultrafine enamel coatings at 800 °C was studied. The results indicated that the three coatings could decrease the mass gains of TiAlNb alloys during discontinuous and cyclic oxidation at 800 °C. However, heavy interdiffusion occurred at the interface of NiCrAlY/TiAlNb during oxidation. Some discontinuous Al2O3 scales formed at interface of NiCrAlY/TiAlNb, where interdiffusion might be depressed. A protective Al2O3 scale could form on TiAlCr coating during oxidation at 800 °C; however, the outward diffusion of Nb and inward diffusion of Cr through the interface and the formation of Al-depletion zone at the subsurface might be detrimental to the long-term oxidation resistance of coating. Enamel coating kept intact during oxidation at 800 °C. But the thermodynamic instability of enamel in contact with TiAl alloys resulted in the formation of an Al-depletion zone and TiSiO3 layer at the interface of enamel/TiAlNb, which would be harmful to the adherence of the enamel coating to the substrate.