Numerical simulation of the plastic behavior of polysynthetically twinned TiAl crystals

A micromechanical model describes the deformation behavior of TiAl intermetallics with a γ-TiAl-α2-Ti3Al lamellar structure. The tension-compression load orientation angle θ varies with respect to the lamellae from 0° ⩽ θ ⩽ 90°. Extended crystal plasticity (ECP) for the γ phase considering the significantly different free paths for dislocations on the various slip systems predicts both the yield stress and the hardening behavior in good agreement with experiment. Neither Mises flow plasticity nor standard crystal plasticity reproduce these results satisfactorily. Near θ = 90°, application of the ECP model for the γ phase also underestimates the yield stress, mainly owing to the representation of the α2 phase by a purely elastic material. Some improvements are suggested by introducing an ECP description also for the α2 phase, distinguishing between pyramidal and prism slip systems.