EFFECTS OF ALLOYING ON CRACK-TIP DEFORMATION AND SHIELDING IN GAMMA-BASED TITANIUM ALUMINIDES

The effects of ternary alloying of Ti-48Al (with 1-3 at.% Mn, Cr and V ), and micro-alloying with 0.2% W, on crack-tip deformation and shield ing mechanisms are discussed in this paper, for failure under cyclic ( Fatigue) loading. Crack-tip deformation mechanisms are elucidated by c rack-lip transmission electron microscopy examination. Twin process zo ne dimensions and the degree of deformation-induced twinning are also determined via optical interference and transmission electron microsco py techniques, respectively. A micromechanics-based model is proposed for the estimation of twin toughening ratios under monotonic or cyclic loading. The model, which is based on non-linear fracture mechanics c oncepts, assumes an average 'smeared' plastic stress distribution acro ss the twin process zone. Differences in the resistance to crack growt h in the ternary alloys are related to intrinsic microstructural Featu res and crack-tip shielding phenomena. Copyright (C) 1997 Acta Metallu rgica Inc.