The analysis of void swelling experiments—part one

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Abstract
In materials under irradiation Frenkel Pairs are produced at a rate proportional to the irradiating flux. Of these defects a fraction (1-α') suffer immediate recombination, and, under neutron or heavy ion irradiation a further fraction of the vacancies condense into vacancy dislocation loops. The effective defect production rates are therefore substantially less than those assumed in previous studies. Moreover the fraction α' is not the same for different types of irradiation. Under electron irradiation the effective bias B becomes B eff = α'electron B while under ion or neutron irradiation B eff becomes B eff = (α'hB—f) where α'electron # α'h. A comparison has been made of the respective void swelling equations with available experimental information under both election and heavy ion irradiation and it has been possible to conclude the following. 1. Using the Heald variable bias model it has been possible to “fit” the rate theory to HVM results in pure copper and 316 and to the VEC experiments in 316 and 321. 2. The ion irradiation results vindicate the subsequent modification to the Heald theory in which competition between neighbouring dislocations is considered. 3. Using the constant bias model, both Cu and 316 HVM results require a bias of about 16% well in excess of the 1–2% originally suggested. 4. Mutual recombination, as distinct from immediate recombination, appears to be important in HVM experiments on Cu and 316. Further experiments are suggested to establish the magnitude of this effect and its dependence on alloying constituents.