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Materialien/Werkstoffe Poster: Do., 13:00–15:30 D-P410
Halogen Ion Implantation and Halogen Treatment as a Tool for improving
the Oxidation Resistance of TiAl-Alloys at High Temperatures
Hans-Eberhard Zschau 1 , Michael Schütze 1 , Horst Baumann 2 , Klaus
Bethge 2
1 DECHEMA e.V., Karl Winnacker Institut, Theodor-Heuss-Allee 25,D-60486 Frankfurt
am Main, Germany – 2 Institut für Kernphysik der Johann Wolfgang Goethe-
Universität Frankfurt am Main, Max-von-Laue-Str. 1, D-60438 Frankfurt am Main,
Germany
γ-TiAl-alloys are of increasing interest in gas turbine and automotive industries because
of their good mechanical properties and of their about 50 % lower specific weight
compared to the presently used Ni-based superalloys. However, due to the poor hightemperature
oxidation resistance of TiAl above 750 ◦ C, the lifetime of components is
limited. Indeed, under such conditions, a non protective mixture of TiO2 and Al2O3
forms during oxidation. The formation of such a protective scale can be stimulated
by the addition of small amounts of halogens, especially of fluorine. In this study the
fluorine is applied in two ways: treatment with diluted HF and ion implantation. As
first method the samples were treated with different aqueous HF solutions between 0.01
and 1.1 m.-% HF. The HF was applied as a drop which covers one side of the samples.
After drying the specimens were oxidized at 10h/900 ◦ C/air. After treatment with 0.06
and 0.11 m.-% HF a dense and 0.8 µm thick protective alumina scale was formed at
the surface. Non destructive Ion Beam Analysis was applied to determine the fluorine
profile within the first 1.3 µm (PIGE) and to measure the elemental profiles of the
main elements Ti, Al and O in the oxide layer down to the sub-surface region (RBS).
From this it was revealed, that the F-maximum is located at the metal/oxide interface.
The fluorine effect is connected with fluorine amounts of about 20 - 22 w.-% at the
surface before oxidation. After the oxidation a maximum of the fluorine concentration
was found within the metal/oxide interface region with values up to 1.1 w.-%. As a
second method fluorine ion implantation was chosen. At 20 keV implantation energy
(projected range of 34 nm) fluences between 10 15 and 5x10 17 F-ions cm −2 were implanted.
After isothermal oxidation (12 h/900 ◦ C/air) a thin alumina scale was formed
for fluences of 5x10 16 and 10 17 F-ions cm −2 . At longer oxidation times a fluence of 10 17
gave the best results. The measured profiles of F, Ti, Al and O are similar to those
obtained after HF treatment. The results proof the proposed mechanism of the fluorine
effect. After finding the optimal parameters for both kinds of fluorine application
the long time stability was studied until 1000h/900 ◦ C/air. In both cases a protective
alumina scale was established. Further investigations concerned with the fluorine loss
during heating. The technical exploitation of the fluorine effect is pointed out.