Improvement of the high-temperature oxidation behaviour of the intermetallic compound γ-TiAl by means of ion implantation

In the present thesis the possibility of the near-surface doping of titanium aluminides for the oxidation improvement by means of ion-beam procedures was studied. Starting from literature knowledge a narrow parameter window for ion implantation of Cl was found. Implantation with a fluence of 1016 cm-2 leads to an optimal protection effect up to 1000 h. This allows at the one hand a surface treatment of TiAl alloys, which has no influence on the surface quality and because of the low depth of the modified layer correspondingly also no negative influence on the mechanical properties of the basic material. The influence of the implantation energy in the range 15 keV to 1 MeV is negligible because very fast diffusion processes in the first minutes of the oxidation occur. It could be shown that the other halogenes Br, I, and F exhibit analogous properties and that the protection effect is independently on further alloy additions also observable in technical alloys. For the first time the effect of chlorine implantations on the high-temperature oxidation behaviour was systematically studied. The models concurring before the begin of the project were discussed. The presented results can only with the model of the catalytic effect of Cl be understood. Other models directly disagree with the observations. The results after implantation of silicon show, that the original improvement of the oxidation behaviour is to be reduced to the formation of titanium silicide. This barrier prevents the diffusion of oxygen. The barrier effect however is not long-time stable. The dissolution could be directly proved for the highest concentration of silicon. A consistent physical picture was discussed. The low-energy implantations of chlorine show a way for the eventual commercial application of the effect. (HSI)