Abstract
The yield stress and microstructure of aluminium quenched under carefully controlled conditions have been correlated by means of transmission electron microscopy. A strongly temperature-dependent form of hardening has been investigated in detail and shown to be associated with submicroscopic vacancy clusters. These defects are probably the ungrown nuclei of the large dislocation loops that are formed concomitantly. Under certain quenching conditions the hardening data agree with the predictions of Fleischer's theory, suggesting that the nuclei are in a collapsed configuration that produces a tetragonal distortion of the lattice. The significance of these results becomes clear from the unified picture that emerges when they are compared with other quenching studies and with neutron-irradiation hardening.
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