The growth of dislocation loops during the irradiation of aluminium

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Abstract
Thin films of zone-refined aluminium have been bombarded at 80°c with a flux of 1.6 × 1010 fission fragments cm−2 sec−1 for various times. Defects can be discerned after 30 sec when the films are viewed in the electron microscope and after longer timès they enlarge into dislocation loops. The larger loops lie near {110} planes with 〈110〉 Burgers vectors. The configuration of the loops and their behaviour on heating suggest that they migrate by a combined conservative climb and slip process. At the higher doses loops lie within the larger loops and the diffraction contrast behaviour suggests that these loops have opposite Burgers vectors, i.e. a vacancy loop is encompassed by an interstitial loop and vice versa. In cases where two loops combine the dislocation interactions confirm this. It is concluded that both vacancy clusters and interstitial clusters form during the bombardment and that initially each type attracts its own; kind and repels the other so that each grows almost independently by a process involving both conservative climb and slip. As they enlarge slip becomes the more important process and near-by loops of the opposite kind, lying on similar slip cylinders slip together, partially cancelling one another. The slip and climb processes are compared, using a simple example where circular prismatic edge dislocation loops interact in aluminium, and found to be compatible with the interpretation. Some implications of the behaviour are given.

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