The role of helium in the development of damage structure and swelling in neutron-irradiated aluminium

Abstract

Abstract Helium and its state of agglomeration in pure aluminium prior to neutron irradiation are investigated with respect to its influence on the microstructural features developed during irradiation to doses of 0·005 to 2·6d.p.a. at about 328 K (0·35 Tm). A level of 4 a.p.p.m. helium, in either submicroscopic form or as small bubbles at the resolvable limit of 2 nm diameter, induces large increases in both the cavity and dislocation components of the damage structure. It also causes swelling to begin much earlier in the neutron dose and to exhibit two different stages of evolution, one early in the dose where the dose exponent of swelling is high, the other at later stages with lower exponent. When the helium is coarsened into 7-nm bubbles by annealing at 0·96 Tm before irradiation it has relatively small effects on damage structure and swelling. The increases in concentrations of cavities and dislocation loops in the presence of helium are attributed to trapping of radiation-produced vacancits by the ...