Plasma-immersion-ion-implantation of fluorine to protect TiAl-components against high-temperature oxidation

Abstract

Titanium aluminides are promising light weight materials for several high-temperature applications, e.g., in aero engines but due to their insufficient oxidation resistance at temperatures above roughly 800 °C they cannot be used yet despite of their good mechanical high-temperature properties. The oxidation behavior of TiAl-alloys can be improved significantly by adding small amounts of fluorine into the subsurface zone of the components (microalloying). One possibility to apply fluorine to the surface of complex TiAl-components is the PI3-technique (plasma-immersion-ion-implantation). The use of an Ar/CH2F2-plasma for the F-PI3 into small coupons led to a positive effect which was as good as the beamline implantation of elemental fluorine gas into samples of the same geometry. Turbine blades, as examples for real TiAl-components, were implanted with an optimumset of parameters. Postexposure investigations like scanning electron microscopy revealed a thin protective alumina scale on the surface of the implanted samples in contrast to a thick mixed oxide scale (TiO2/Al2O3) growing on untreated samples during high-temperature oxidation in air. The hightemperature oxidation resistance of several TiAl-alloys was improved by plasma-immersionion-implantation of fluorine. Small coupons showed a much lesser oxidation during high-temperature exposure after fluorine treatment than untreated samples. The performance of turbine blades for the low pressure compressor of a new generation of jet engines was also improved. Fluorine treated samples are covered with a thin, protective alumina scale after high-temperature exposure in air instead of a fast growing, nonprotective mixed oxide (TiO2/Al2 O3) scale which is found on untreated samples. A picture is presented. © 2009 Wiley-VCH GmbH & Co. KGaA, Weinheim.