A micro-mechanical investigation was made of the deformation behavior of TiAl-based alloys with a 2-phase microstructure that comprised the -TiAl phase and a small volume fraction of the 2-Ti3Al phase at room temperature. The model was based upon the unit cell technique, in which a 3-dimensional unit cell represented the microstructure. The main deformation mechanisms in the -TiAl phase (normal slip, true twinning) were incorporated into the model. Slip was modelled by crystal plasticity, and deformation twinning was included by assuming a constitutive law that was analogous to Schmid’s law for crystallographic slip. This micro-mechanical model was used to simulate uniaxial tests of so-called polysynthetically twinned TiAl crystals which contained only a single set of parallel -TiAl and 2-Ti3Al lamellae with a specific orientation. Stress-strain curves were calculated numerically for various lamellar orientations, and the predicted yield stresses were compared with experimental ones. The model was able to explain the deformation mechanisms in detail. In particular, it predicted the twin volume fractions in the -TiAl phase and confirmed the importance of twinning as a deformation mechanism.

S.M.Schlögl, F.D.Fischer: Philosophical Magazine A, 1997, 75[3], 621-36