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

Titanium aluminides with a lamellar microstructure consisting of the i ntermetallic phases alpha(2)(Ti3Al) and gamma(TiAl) suffer from brittl eness at ambient temperatures but exhibit, at the same time, a relativ ely high fracture toughness. This discrepancy indicates that the lamel lar interfaces may play an important role in stabilizing crack propaga tion. In this context the present paper reports an electron microscope study of crack propagation in the lamellar morphology of two-phase ti tanium aluminides. Special emphasis was paid to the interaction of cra cks with lamellar boundaries and the related processes of crack tip pl asticity. The processes observed are analysed with respect to their ef ficiency for crack tip blunting or shielding.