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Materialien/Werkstoffe Poster: Do., 13:00–15:30 D-P400
Microstructure and Residual Stress Formation in Oxide Layers Grown on
High Niobium Containing γ-TiAl Based Alloy
Pedro Silva 1 , Haroldo Pinto 1 , Alexander Kostka 1 , Harald Chladil 2 , Helmut
Clemens 2 , Anke Pyzalla 1
1 Max-Planck Institute for Iron Research, Max-Planck Str.1, 40237 Düsseldorf, Germany
– 2 Montanuniversität Leoben, Department Metallkunde und Werkstoffprüfung,
8700 Leoben, Austria
Due to their low density, high mechanical strength and creep resistance at elevated
temperatures titanium aluminides are considered as promising structural materials
for high temperature applications in the aerospace and automotive sectors. The 3rd
Generation of TiAl alloys (so called TNB alloys) are characterized by a high Nb-content.
In particular, these high Nb containing alloys with the baseline composition Ti-(42-
45)Al-(5-10)Nb+X (at%) have attracted attention due to their combination of high
creep strength, good ductility at room temperature and excellent oxidation resistance.
The ternary Ti-Al-Nb system is known to enable the formation of a variety of mixed
oxide scales depending on the chemical alloy composition and oxidation temperature.
However, the phase composition is a decisive criterion for the shielding efficiency of
these oxide layers, since a dense single protective Al2O3 layer may deteriorate to a
porous, less protective mixed oxide scale. Therefore, the knowledge about the mechanisms
of oxide formation in these new alloys is essential for the determination of
conditions necessary for the development of dense oxide layers with both mechanical
integrity and diffusion barrier properties.
The aim of this study is a characterization of oxide layers formed on γ-TiAl alloys with
high Nb-contents after oxidation at 800 ◦ C. The microstructure of the oxide layers, the
interface between the substrate and oxide layer as well as layer integrity are studied by
synchrotron x-rays and electron microscopy. The results reveal the spatial arrangement
of the different oxides within the nanostructured oxide layer. The oxide scales are
quantitatively analyzed by Rietveld refinements. The phase specific residual stress
state is evaluated using synchrotron X-ray diffraction at low incidence angles.