The effect of stress and subgrain size on the creep behavior of high purity aluminum

Abstract

The effect of stress reductions, made in the steady stale creep region, on the strain rate and subgrain size in high purity aluminum were studied. After a stress reduction the strain rate remains constant or decreases slightly for a finite time interval which depends on the magnitude of the stress reduction. The strain rate then increases, after this incubation period, for samples deformed at the reduced stress. Microscopic observations reveal that this strain rate increase is accompanied by an increase in subgrain size. No change in subgrain size is observed during the incubation period. There is a definite relationship between strain rate and subgrain size, after a stress reduction, in the time interval in which the strain rate is constant or is increasing. A phenomenological equation is developed which describes the strain rate during this transient period which includes stress and subgrain size as important parameters.