The oxidation behavior of TiAINb 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 NiCrAIY/TiAlNb during oxidation. Some discontinuous Al2O3 scales formed at interface of NiCrAIY/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. (c) 2004 Published by Elsevier B.V.