Efficient oxidation protection of Ti- and TiAl-alloys by F-treatments

Ti-alloys suffer from high oxidation rates and oxygen uptake during exposure in oxidizing environments at temperatures above approximately 600 degrees C. Technical TiAl-alloys have the same problem due to the insufficient oxidation resistance at temperatures above 750 degrees C. The use of these lightweight alloys is hence limited. The fluorine effect is a very promising way to improve the oxidation resistance of TiAl-alloys. Defined amounts of fluorine in the surface zone of TiAl-components change the oxidation mechanism. A protective alumina layer is formed which prevents further oxidation and subsequently allows the use of this new alloy family in several high temperature applications. The Al-content of standard Ti-alloys is not enough to get the fluorine effect to operate but after Al-enrichment of the surface zone a subsequent fluorination leads to the same results. In this paper results of oxidation tests of untreated and treated Ti- and TiAl-alloys will be presented and their behavior compared.