THE ROLE OF ORDERED DOMAINS AND SLIP MODE OF ALPHA-2 PHASE IN THE PLASTIC BEHAVIOR OF TIAL CRYSTALS CONTAINING ORIENTED LAMELLAE

TiAl crystals containing a single set of lamellae composed of the alpha2 and gamma phases were grown using the floating zone method. The lamellar spacing was controlled in the range between 0.37 and 1.8 mum. The plastic behaviour of these crystals depends strongly on the deformation mode of alpha2 phase, the domain size and the lamellar spacing. When the stress is applied parallel to the lamellar planes, shear deformation occurs across the lamellae and the {1010BAR} prismatic slip is activated in the alpha2 phase. For specimens with the loading axis perpendicular to the lamellar planes, the {1121BAR} pyramidal slip occurs with application of high stress. The mode of deformation in the alpha2 phase is responsible for a large anisotropy of plastic behaviour of TiAl containing lamellae. The lamellar spacing and the domain size affect the yield stress similar to the effect caused by grain size. The lamellar boundaries between thin alpha2 plates and gamma phase provided more effective strengthening than the domain boundaries.