Creep behaviour of Ti-6Al-2Sn-4Zr-2Mo: II. Mechanisms of deformation

Abstract Constant load creep tests are performed in Ti-6242(Si) alloy with a lath microstructure, at temperatures of 538 and 565 °C. A change in the stress exponent values from ~1 at low stresses to between 5 and 7 at high stresses, is indicative of a change in creep mechanism. TEM analysis indicates that the deformation is dominated by a -type 1 / 3 2 0 dislocations in the α phase, with little evidence of dislocation activity in the β laths. At higher stress (310 MPa), the a -type dislocations are pinned frequently along their screw direction by tall jogs. A creep model is proposed based on the premise that movement of these jogged screw dislocations may control the creep rate. In contrast, at low stress (172 MPa), the a -type dislocations have long straight screw segments with no apparent pinning points. The near-edge segments are in climb configurations. The creep rates here are close to those predicted, based on Harper–Dorn creep, although the dislocation density is larger than that normally associated with this regime.