An investigation of the stress exponent and subgrain size in Al after stress reduction

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Abstract
Stress-change and uninterrupted tests were performed on Al over the high-temperature range 0·65–0·99T m, where T m is the melting point, and at stresses varying from 7 × 10−6 G to −2 × 10−4 G, where G is the shear modulus. In addition, dislocation substructure that developed during creep was examined by means of the etch-pit technique and transmission electron microscopy. By comparing the mechanical and substructural data of stress-reduction tests with those obtained in uninterrupted tests, two observations are made. First, the stress exponent inferred from stress-reduction tests is essentially equal to that obtained from uninter rupted tests. Second, as a result of stress reduction, the subgrain size coarsens and reaches the new steady-state value whicli would be attained in an uninterrupted test at the reduced stress. Evidence of subgrain coarsening is demonstrated not only by changes in size, but also by relevant substructural phenomena, such as subgrain-boundary dissolution, which are noted during the transient period after the stress reduction.