Evaluation of thermodynamic data for an advanced γ-TiAl CALPHAD database
Within the EU project „ADVANCE - Sophisticated experiments and optimisation to advance an existing CALPHAD database for next generation TiAl alloys” MPIE is collaborating with Thermocalc-Software AB, Stockholm, Montanuniversität Leoben and Helmholtz-Zentrum Geesthacht. At MPIE the focus lies on the production and heat treatments of model alloys. By analysing them through metallography, X-ray diffraction, electron probe microanalysis and differential thermal analysis, the necessary data are obtained. Colleagues in Leoben perform atom probe tomography and transmission electron microscopy and in Geesthacht in situ synchrotron X-ray diffraction is carried out. All obtained data are optimised at the company Thermocalc and checked for consistency before they are implemented into the database.
Alloys based on the intermetallic phase γ-TiAl constitute a new class of materials. They have high specific strength and are therefore specifically suited for applications where the weight of moving parts has to be considered, e.g. compressor blades in aero engines or turbo chargers for vehicles. Compared to established Ni- and Co-base superalloys, γ-TiAl alloys are lighter and therefore more energy efficient.
Todays alloy developments crucially depend on data-based CALPHAD programs. CALPHAD is an acronym for calculation of phase diagrams. The databases contain specific thermodynamic values for phase equilibria and phase transformations, and compositions of the phases in dependence on temperature and composition of an alloy. The databases allow to calculate which phases are stable at certain temperatures, their volume fractions and compositions within regions, where no experimental results are available. This enables prediction of the microstructures and, from this, conclusions about expected mechanical properties. Thereby, employment of these databases enables a time-efficient development of novel materials.
Example of an aligned microstructure of a Ti-Al-Nb alloy.