Void formation and growth in copper-nickel alloys during irradiation in the high voltage electron microscope

The formation and growth of voids during irradiation in a high voltage electron microscope were studied in copper and Cu-Ni alloys. For each composition the range of irradiation temperatures from 250 C to 550 C was covered. The development of the irradiationinduced dislocation structure was also studied.

At irradiation temperatures up to 450 C the void swelling decreased rapidly with increasing Ni content and became practically zero for Cu-10%Ni. The decrease in swelling was produced mainly by decreased void growth (and not by decreased void number density). At 550 C the void swelling increased with increasing Ni content up to 5%, whereas for Cu-10%Ni the swelling became practically zero; again the changes in swelling with Ni content were mainly determined by changes in void growth.

The reduction in void swelling and growth due to alloying is ascribed to vacancy or interstitial trapping at submicroscopic Ni precipitates, i.e. to the precipitates acting as recombination centres. The increase in void swelling and growth with increasing Ni content, on the other hand, is ascribed to dislocation climb sources which emit loops and hence produce a fairly high dislocation density at a temperature where there are only few dislocation in pure copper or Cu-Ni with lower Ni content.