Deformation Behaviour of Gamma Titanium Aluminides

The present work, dealing with the micromechanical modeling of the deformation behavior of -TiAl based alloys, is characterized by a strong interaction between numerical simulation facilities and detailed experimental investigations. In the first part of the studies a micromechanical model describing the deformation behavior of polycrystalline - TiAl-based alloys exhibiting a globular "near-" microstructure was developed and presented. The model works with crystallographic slip and mechanical twinning based on the concepts of crystal plasticity. The global stress- strain behavior of non-textured and weak-textured near- alloys is computed and compared with results from mechanical tests. Simulations and experiments of compression tests and tensile tests applying different strain rates match well with respect to the global stress-strain curves as well as the onset of mechanical twinning. In the second part of the work the creep behavior of a "designed fully lamellar (DFL)" -TiAl based alloy is investigated. Depending on the cooling rate, the interface spacings in the polycrystalline material can be differently adjusted. Creep tests at various temperatures under a constant load indicate that the minimum creep strain rate decreases monotonically with decreasing interface spacing. Creep tests performed on this sheet material do not show any grain boundary sliding. The main creep deformation mechanism under the given conditions appeared to be diffusion-controlled dislocation climb. The presented micromechanical modeling concept confirms that a power law creep model can describe the creep behavior of DFL microstructures if a structure factor depending on the lamellar orientations and the mean lamellar interface spacing is introduced.