AN ELECTRON-MICROSCOPE STUDY OF DEFORMATION AND CRACK-PROPAGATION IN (ALPHA(2)+GAMMA) TITANIUM ALUMINIDES

Titanium aluminides with a lamellar microstructure consisting of the intermetallic phases alpha(2)(Ti3Al) and gamma(TiAl) suffer from brittleness at ambient temperatures but exhibit, at the same time, a relatively high fracture toughness. This discrepancy indicates that the lamellar interfaces may play an important role in stabilizing crack propagation. In this context the present paper reports an electron microscope study of crack propagation in the lamellar morphology of two-phase titanium aluminides. Special emphasis was paid to the interaction of cracks with lamellar boundaries and the related processes of crack tip plasticity. The processes observed are analysed with respect to their efficiency for crack tip blunting or shielding.