MICROMECHANICAL MODELING OF TIAL INTERMETALLICS

The mechanical properties of gamma-TiAl based alloys with a two phase microstructure composed of the gamma-TiAl phase and a small volume fra ction of the alpha(2)-Ti3Al phase are determined by the microstructure . A single grain with a lamellar microstructure shows anisotropic plas tic behavior which can be best seen in yield stresses depending on the orientation angle theta between the load axis and the lamellar bounda ries. To describe these deformation characteristics a micromechanical model is developed which considers the main deformation mechanisms in the gamma-phase, namely ordinary slip and deformation twinning, The mo del delivers stress-strain curves for various orientation angles theta (0 degrees less than or equal to theta less than or equal to 90 degre es), twin volume fractions in the ordered domains of the gamma-TiAl ph ase and the contribution of deformation twinning to the total deformat ion. The computed yield stresses for tension and compression are compa red with the experimental ones, It turns out that no significant diffe rence exists between the yield stresses in tension and compression des pite of the unidirectionality of deformation twinning.