Abstract
Stress dependence of creep rates and the level of internal stress, as well as transient behavior upon sudden stress changes during the steady-state creep were studied. The stress exponent for steady-state creep rates, n, depended on the stress level. In the stress region lower than 7 MPa, n was about 5 and the inernal stress was nearly equal to the applied stress. The steady-state creep in this region is controlled by a recovery process, though dislocations glide viscously. In the stress region between 7 and 30 MPa, n was about 3. In the stress region higher than 30 MPa, n became again larger than 3. In these two regions, where the internal stress was obviously less than the applied stress, the role of viscous gliding of dislocations becomes important and cannot be neglected in the discussion of the total process of creep. Transition from the middle to the high stress regions was found to arise from the change in the stress dependence of dislocation density. These results indicate that the change in n does not necessarily correspond to the change in the creep mechanism.
