It was recalled that creep stress exponents of the order of 5 were typically associated with dislocation processes, and with a strong tendency to sub-grain formation. It was demonstrated that there were several important alloy systems that exhibited similar stress dependences, but lacked the tendency to sub-grain formation. Thus, dislocations in γ-TiAl and in the hexagonal close-packed α-phase of Ti-6242, tended to be homogeneously distributed and exhibit a tendency to alignment along screw orientation. In both systems, the screw dislocations had a high density of pinning points which, detailed transmission electron microscopic investigation indicated, were the locations of tall jogs. These observations suggested that the jogged-screw model for creep would be appropriate; after making a suitable allowance for the presence of the tall jogs. A modified jogged-screw model was presented, and the results were shown to compare favorably with experiment for both alloy systems. Possible criteria for the formation of tall jogs were also considered.

Application of a Modified Jogged-Screw Model for Creep of TiAl and α-Ti Alloys. G.B.Viswanathan, S.Karthikeyan, R.W.Hayes, M.J.Mills: Metallurgical and Materials Transactions A, 2002, 33[2], 329-36