The department „metal physics“ develops novel titanium aluminide alloys (TiAl) for applications at elevated temperatures in aero engine turbines and automotive engines. In addition to the improvement of TiAl-alloy properties also processing by the cast and forging route is investigated. An emphasis is laid on the further development of the powder metallurgical route for TiAl and titanium alloys.
In addition the department also investigates other selected metallic/intermetallic materials for high temperature application as for example L12-hardened Ni- and Co-base superalloys. In all these investigations advanced characterisation methods are employed. Most prominent are high resolution and conventional transmission electron microscopy as well as diffraction experiments in in-situ specimen environments at the Helmholtzzentrum Geesthacht run beamlines of the German Electron Synchrotron (DESY).
Turbocharger wheels of a TiAl alloy. Photo: HZG
Intermetallic TiAl based alloys are more and more employed for applications in the temperature range up to 800 °C due to their good specific strength. Actual application fields are aero engine turbines and turbochargers in automotive engines.
The research activities of the department concentrate on the ongoing development of TiAl-alloys and related processing methods including powder metallurgy, casting and forging. It is essential to understand the underlying mechanisms which determine the mechanical properties and how alloy composition and processing conditions influence them. Thus, we characterise the microstructure and behavior of this alloy system in depth. This includes atomic defect structures and mechanical properties.
Microstructure of a novel nanoscale TiAl alloy and tensile test curves that show the excellent combination of high strength and good ductility at temperatures up to 700 ° C. Photo: HZG
An emphasis of the activities in the field of processing lies on powder metallurgical routes for titanium and TiAl alloys. For that purpose we employ a gas atomisation unit (PIGA) suited for titanium and TiAl powders. Either cold crucibles or contactless atomisation in the so called EIGA process are employed to overcome problems with the extreme susceptibility of titanium and TiAl alloys for even low levels of impurities. In addition we have equipment for powder handling and characterisation.
Novel Co-base superalloys
Y/Y' micro-structure of a new Co-base superalloy - the diffraction pattern shows the reflections of the cubic matrix and the ordered, coherently embedded precipitation phase. Photo: HZG
By the precipitation of an intermetallic phase in the ternary system Co-Al-W it is possible to achieve mechanical properties on par with nickel-base superalloys at elevated temperatures. While these Co-alloys show a number of similarities with the well known nickel-base superalloys nevertheless important questions with respect to mechanisms of plastic deformation, phase constitution, microstructure development and physical properties are open. These topics are addressed by our research on these materials which we either perform independently or in cooperation with university partners. These basic investigations lay the foundation for a later development of commercial alloys.