Measurements of fluorine depth-profiles on TiAl turbine blades using ion beam analytical techniques

Abstract

Intermetallic TiAl alloys are foreseen to substitute Ni-based alloys in several high-temperature applications such as turbine blades for aeronautics. Because of their low density the mass of these components could be reduced by half. However, a mixed oxide scale of TiO2 and Al2O3 which provides no oxidation protection is growing at temperatures above 700 °C. By means of the halogen-effect the high-temperature oxidation resistance of TiAl alloys can be improved by orders of magnitude. Therefore fluorine was introduced into turbine blades using two different chemical fluorination methods. The application of a fluorine treatment promotes the growth of a pure and dense alumina scale which prevents the alloy from increased oxidation. In previous work it has been shown that an appropriate fluorine content after oxidation and its location beneath the surface are indicators of a successful fluorine effect. In the present work, the fluorine content was measured before and after oxidation of TNB alloy as a function of depth by using proton induced gamma-ray emission (PIGE) in a specially designed vacuum chamber at the 2.5 MV van-de-Graaff accelerator at the IKF. Additionally, composition and thickness of the oxide scale was determined by Rutherford backscattering spectrometry (RBS). The ion beam techniques are non-destructive and thus offer a method for quality assurance of the halogen treatment.