The role of ordered domains and slip mode of α2 phase in the plastic behaviour of TiAl crystals containing oriented lamellae

Abstract

TiAl crystals containing a single set of lamellae composed of the α 2 and γ phases were grown using the floating zone method. The lamellar spacing was controlled in the range between 0.37 and 1.8 μm. The plastic behaviour of these crystals depends strongly on the deformation mode of α 2 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 {10 10} prismatic slip is activated in the α 2 phase. For specimens with the loading axis perpendicular to the lamellar planes, the {11 21} pyramidal slip occurs with application of high stress. The mode of deformation in the α 2 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 α 2 plates and γ phase provided more effective strengthening than the domain boundaries.