NUMERICAL-SIMULATION OF THE PLASTIC BEHAVIOR OF POLYSYNTHETICALLY TWINNED TI-AL CRYSTALS

A micromechanical model describes the deformation behavior of Ti-Al in termetallics with a gamma-Tial-alpha(2)-Ti3Al lamellar structure. The tension-compression load orientation angle theta varies with respect t o the lamellae from 0 degrees less than or equal to theta less than or equal to 90 degrees. Extended crystal plasticity (ECP) for the gamma phase considering the significantly different free paths for dislocati ons on the various slip systems predicts both the yield stress and the hardening behavior in good agreement with experiment. Neither Mises n ow plasticity nor standard crystal plasticity reproduce these results satisfactorily. Near theta = 90 degrees, application of the ECP model for the gamma phase also underestimates the yield stress, mainly owing to the representation of the alpha(2) phase by a purely elastic mater ial. Some improvements are suggested by introducing an ECP description also for the alpha(2) phase, distinguishing between pyramidal and pri sm slip systems.