PM 06 Advances in Intermetallic-Based Alloys for Structural and Functional Applications November 26-November 29 , 2018 Symposium Organizers

Intermetallic Titanium Aluminid based alloys are considered for high-temperature aero and automotive engine applications. The advantage of this class of innovative high-temperature materials is their low density in combination with good strength and creep properties up to 850°C. A drawback, however, is their limited damage tolerance at room temperature, which is reflected in a low plastic fracture strain and fracture toughness. Advanced engineering Titanium Aluminid alloys are complex multi-phase materials which can be processed by ingot or powder metallurgy. Engine components can be manufactured by casting as well as additive manufacturing, e.g. electron beam melting. Each ingot production process leads to specific microstructures which can be optimized by thermo-mechanical processing, e.g. isothermal or hot die forging and subsequent heat treatments. Thermo-mechanical processing can provide balanced mechanical properties, i.e. a minimum ductility at room temperature as well as sufficient creep strength at elevated temperature. In order to achieve this goal, the knowledge of the occurring solidification processes and phase transformation sequences is essential. Therefore, thermodynamic calculations were conducted to predict the phase diagram of engineering TiAl alloys. After experimental verification, these phase diagrams provided the basis for the development of heat-treatments. To account the influence of deformation and kinetic aspects sophisticated exand in-situ methods have been employed to investigate the evolution of the microstructure during thermo-mechanical processing. For example, in-situ high-energy X-ray diffraction was conducted to study dynamic recovery and recrystallization processes during hot-deformation tests. Novel high-strength Titanium Aluminid based alloys, such as TNM alloys have been developed in the last decade to meet the advanced requirements of aero engines.These alloys are characterized by a high content of β-stabilizing alloying elements, such as Nb and Mo. Because Nb and Mo represent the decisive alloying elements, this alloy family, based on the γ-TiAl phase, has been named “TNM alloys” in order to distinguish them from the well-known and even stronger “TNB alloys” which rely on a high Nb concentration and small additions of B and C. At room temperature, strength levels > 1000 MPa can be achieved in advanced TiAl alloys by appropriate thermo-mechanical processing and subsequent heat treatments. It is important to note that also high temperature properties, such as creep resistance, were considerably improved, e.g. by implementation of precipitation hardening, which further extend the application range of Titanium Aluminid based alloys.