During high-temperature creep of the γ-phase L10 structure of a so-called near-gamma Ti-48Al microstructure, transmission electron microscopic observations indicated that a/2<110] (unit) dislocation activity was a predominant deformation mode. The unit dislocations tended to be elongated along the screw orientation, and to exhibit a large number of localized pinning points. Tilting experiments demonstrated that these pinning points were associated with jogs on the screw dislocations, thus suggesting that the jogged-screw model for creep should be appropriate in this case. It was shown that, in its conventional form, the jogged-screw model was incapable of reproducing the measured creep response; for example, with respect to stress exponents or absolute creep rates. Microscopic observations also demonstrated that a spectrum of jog heights was present, with some being as high as 40nm. A modification of the jogged-screw model was proposed in which the average jog height was assumed to depend upon stress. This modified model resulted in good agreement between predicted and measured creep rates.

Modification of the Jogged-Screw Model for Creep of γ-TiAl. G.B.Viswanathan, V.K.Vasudevan, M.J.Mills: Acta Materialia, 1999, 47[5], 1399-411