純アルミニウムの高温における遷移クリープ機構

抄録

In order to clarify the deformation mechanism in the transient creep region, the instantaneous plastic strain and the strain rate have been measured precisely by using pure aluminum from a very early stage of transient creep to the steady state. The creep test has been carried out at temperatures from 623 K to 823 K and at stresses from 0.81 to 6.7 MPa.
It is found that the instantaneous plastic strain depends not on temperature but exclusively on stress. At a very early stage of transient creep, the Zener-Hollomon parameter, Z, depends strongly on temperature in the lower temperature region (623-723 K) but not on temperature in the higher temperature region (773-823 K). At the later stage, the Z vs. strain curve converges to a single one, which is the same as that in the higher temperature region, and finally comes into the steady state.
From the temperature-independence, it is concluded that the main part of instantaneous plastic strain is produced by the athermal motion of dislocations, and from the theroetical analysis based on a dislocation-network model it is inferred that the creep mechanism in the lower temperature region changes from a process, in which the thermally activated glide of some long dislocation links takes part, to the well-known recovery process at an early stage of transient creep.