Improvement of oxidation resistance of γ-TiAl At 800 and 900°C in air by TiAl2 coatings

In the present work, gamma-TiAl and TiAl2 coatings with the thickness of about 20 mu m were made on gamma-TiAl substrates by using a close-field magnetron sputter deposition (CFMSD) technique. The coatings showed good quality with no micro-cracks being observed in the as-deposited TiAl2 coating cross-sections. Oxidation exposure tests at 800 and 900 degrees C in air were carried out to assess the oxidation resistance of the coatings and the cast gamma-TiAl. The gamma-coating and cast TiAl showed similar oxidation performance. Both of them had suffered great oxide losses with the formation of Al2O3 + TiO, mixtures and no Al2O3-rich layer was found in either case. By contrast, only external Al2O3 layers with a theta-phase structure was formed on the TiAl2 coatings at 800 and 900 degrees C, and the theta-Al2O3 scales showed high protective ability with low mass-gains and good scale adherence. After the oxidation exposures, the TiAl2 coating remained to be almost free of micro-clacks, and an inter-diffusion region of about 5 mu m was observed between the TiAl2 coating and the gamma-substrate, which could act as a metallurgical bonding between the coating and substrate. (c) 2005 Elsevier B.V. All rights reserved.