Intermetallic Materials

Intermetallic Materials (M. Palm, F. Stein)

Group Mission. Fundamental research on phase stability and phase transformations of intermetallic phases and establishing properties to elucidate the possibilities of their industrial application are the two aims of the Intermetallic Materials group.

A sound knowledge of the phase equilibria in dependence of composition and temperature is the basis for any kind of materials development. For intermetallic materials this information is often lacking, which is partly due to considerable experimental difficulties in investigating these high-melting materials. Therefore, besides metallography, XRD, EPMA and DTA, additional methods such as in situ neutron diffraction [70,71] and advanced TEM techniques are employed [72,73]. In addition, the diffusion couple technique is widely used for a rapid study of phase equilibria [74,75]. In order to evaluate the potential for industrial application, fundamental mechanical properties such as hardness, yield strength and creep resistance and the basics of the oxidation behaviour in air are studied [76].

The group has tight connections with the neighbour departments, especially on the topics of ab-initio thermodynamics [77,78] and corrosion [79], and multiple international collaborations                        [70,71,73,74,80,81]. The development of intermetallic materials for structural applications is performed in close cooperation with industry [82].

Research Highlights 2009-2010. Currently, Laves phases and Fe and Ti aluminides are the main topics of research. The stability of the different crystallographic structures of the Laves phases in dependence on temperature and composition and their effect on mechanical behaviour are studied in detail. For Fe-Al-based materials a long lasting problem has been solved with the determination of the crystallographic structure of the high-temperature phase ε (Fe5Al8, cubic, space group I-43m) [83]. In view of the practical application of Fe-Al, considerable progress was obtained by the development of a forging route [82] and the characterisation of the microstructure and mechanical properties in different parts of a forged steam turbine blade [84]. Within the framework of a larger programme, the complex phase transformations and resulting mechanical properties of Al-rich Ti-Al alloys have been investigated   [72,85]. These TiAl + Al2Ti alloys offer a reasonable creep resistance, especially in view of their low density (3.8 g/cm3) and in that they  show an improved oxidation resistance compared to established TiAl alloys. However, even generating lamellar TiAl + Al2Ti microstructures only results in a minor increase in ductility of these rather brittle materials.

References

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