Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

TiAl-intermetallics show great potential for applications in high temperature-components due to their low density and excellent high-temperature strength. Their major drawback is the oxidation resistance at temperatures above 750°C. It has been shown that one way to improve this resistance by several orders of magnitude is the fluorination of the surface zone of the material. This fluorine treatment occurs at low temperatures and influences only the surface region of the components, so that the bulk properties are not affected. The fluorination changes the oxidation mechanism during subsequent oxidation exposure at temperatures higher than 750°C in such a way that the formation of a thick mixed oxide scale is replaced by the growth of a thin protective alumina scale. No additional coatings are necessary for the full protection of the substrate against further oxidation. One efficient and simple technique for bring the fluorine onto the TiAl surface is by using different liquid phases. This work focuses on the influence of liquid phase composition on the lifetime of the protective alumina layer. Possible beneficial synergistic effects between F and Si on the oxide nucleation behaviour are discussed in comparison to alternative fluorination methods such as plasma immersion ion implantation. Furthermore, the influence of the high temperature exposure needed for the initiation of the change in the oxidation mechanism of TiAl-alloys (i.e. conventional furnace exposure versus short-time laser treatment) on the stability of the protective character of alumina is examined.