The dislocation distribution in face-centred cubic metals after fatigue

Transmission electron microscope observations of fatigued Cu, Ni and Au show that these metals contain a high density of dislocation loops. Similar results have been obtained for stainless steel fatigued at high stress. Some of these loops are elongated in a direction normal to the Burgers vector, which suggests strongly that they are formed from sessile jogs in screw dislocations. No correlation between surface slip striations and dislocation distribution has been found.The observed distribution of loops explains the absence of asterism on X-ray photographs reported previously. Furthermore, the loops are observed to anneal out in a temperature range in which the stored energy is released, and the fatigue hardening disappears. Fatigue hardening is discussed in terms of loops; the annealing of the loops is also considered in detail.