Constant-load creep tests were performed on Ti-6242(Si), with a lath microstructure, at 538 to 565C. A change in the stress exponent, from about unity at low stresses to between 5 and 7 at high stresses, reflected a change in creep mechanism. Transmission electron microscopic analysis indicated that deformation was dominated by a-type 1/3<11•0> dislocations in the α-phase, with little evidence of dislocation activity in the β-laths. At higher stresses (310MPa), the a-type dislocations were frequently pinned along their screw direction by tall jogs. A creep model was proposed which was based upon the idea that the movement of these jogged screw dislocations controlled the creep rate. At low stresses (172MPa), the a-type dislocations had long straight screw segments with no apparent pinning points. The near-edge segments were arranged in climb configurations. The creep rates were close to those predicted on the basis of Harper–Dorn creep, although the dislocation density was higher than that normally associated with that regime.

Creep Behaviour of Ti-6Al-2Sn-4Zr-2Mo - II. Mechanisms of Deformation. G.B.Viswanathan, S.Karthikeyan, R.W.Hayes, M.J.Mills: Acta Materialia, 2002, 50[20], 4965-80