抄録
Sudden stress-increase tests were carried out during creep of the α-phase materials of Ti–Al system containing 27.5 and 34.0 mol%Al at 1150 K and 1250 K under 126 MPa which is well located within the low stress region. The range of stress increase Δσ was from 3 MPa to 18 MPa.
The type of transient creep curves is essentially the sigmoidal one. The instantaneous increase in creep rate Δ\dotε is proportional to Δσ. These results indicate that dislocations move viscously in near-steady-state creep in these materials. The apparent mobility obtained from Δ\dotε, i.e. (Δ\dotε⁄\ ildeD)⁄Δσ, is independent of temperature and composition, where \ ildeD is the interdiffusion coefficient, which is almost independent of the composition in the α2 phase.
In the near-stoichiometric material, however, the type of transient creep curves changes from the sigmoidal one to the normal one, when the stress increase exceeds a critical value. The value of Δ\dotε becomes to be improportional to Δσ under these high stresses. These results suggest that dislocations can move jerkily and the multiplication can occur under these conditions.
