A. Donchev, J. Grüters, M.C. Galetz, M. Schütze
The oxidation resistance of γ-TiAl alloys can be dramatically improved by the fluorine effect. The Al content is a critical factor. It has to be above at least 40 at.% to get the fluorine effect to operate. Alloys with an Al content near this value or below have to be enriched with Al in advance. For this purpose, aluminisation is one possibility. The Al content within the diffusion layers can be determined by variation of the pack parameters, i.e. Al activity, time and temperature. These Al-rich diffusion layers form a protective alumina layer during high-temperature exposure in oxidising environments, but they have to be treated subsequently with fluorine to stabilise their protective effect. Results of high-temperature exposure tests of several untreated and treated alloys will be presented in this paper. Post experimental metallographic investigations reveal the formed oxide scales so that the effects can be rated. Finally, the results will be discussed in view of the known fluorine effect for technical TiAl alloys.