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The intermetallic Titaniumaluminides are expected to have a high potential as material in high temperature technology. Their high specific strength at temperatures above 700°C offers the possibility for manufacturing components of aerospace and automotive industries. With a specific weight of 50% of that of the widely used Ni-based superalloys TiAl is very suitable for fast rotating parts like turbine blades in aircraft engines and land based power stations, exhaust valves or turbocharger rotors. Thus lower mechanical stresses and a reduced fuel consumption are expected. In contrast to these benefits TiAl shows insufficient oxidation resistance at temperatures above 750°C (Rahmel et al., 1995). To reach higher service temperatures a protective alumina scale would be needed. A surface modification avoids any detrimental influence on the excellent mechanical properties of the material. By using the “halogen effect” a dense protective alumina scale was formed after doping the metal surface with small amounts of chlorine (Kumagai et al., 1996; Schütze & Hald, 1997; Donchev et al., 2003; Schumacher et al., 1999a; Schumacher et al., 1999b; Hornauer et al., 1999). The halogen effect can be explained by a thermodynamic model assuming the preferred formation and transport of volatile Alhalides through pores and microcracks within the metal/oxide interface and their conversion into alumina, forming a protective oxide scale on the surface (Donchev et al., 2003). However the alumina scale fails during thermocyclic loading of Cl-implanted TiAlsamples. Based on this model comprehensive calculations have been performed for fluorine and TiAl predicting a positive effect. The results of thermodynamical calculations have to be transformed into F-concentrations. The beam line ion implantation is chosen as a method of F-application because of its accuracy and reproducibility. By varying the implantation parameters optimal conditions have to be determined to meet the region of F-amounts necessary for a positive F-effect. The implanted F-depth profiles can be verified by the non-destructive ion beam analysis method PIGE (Proton Induced Gamma-ray Emission). The alumina scale formed via the F-effect is adherent even under thermocyclic conditions. However technical use is only possible if the fluorine effect can be stabilized for a time of at least 1000 hours. Hence after the alumina scale formation the stability of oxidation protection depends on the behaviour of the implanted fluorine vs.

Surface Modification by Ion Implantation to Improve the Oxidation Resistance of Materials for High Temperature Technology