The role of superdislocations for modeling plastic deformation of lamellar TiAl

The deformation behaviour of lamellar TiAl-alloys is investigated by means of micromechanical finite element simulations. For the simulations, a lower and an upper bound periodic unit cell representing the lamellar substructure are used. Crystallographic slip is described by continuum crystal plasticity. For the simulations, 16 individual ordinary, super, and twinning systems divided into three morphological slip modes are taken into account. The strength and hardening parameters of the slip systems are determined by comparison with experimental data from room temperature compression tests of poly-synthetically twinned (PST) crystals of TiAl. The effect of the yield stress of the superdislocations is investigated by systematic parameter variations. The results show that the general anisotropy of PST-crystals can already be described with a purely morphological classification of the slip systems. Superdislocations cause a slight tension–compression anomaly if the yield stresses are higher than for the ordinary and twinning systems.