The He gas bubble superlattice in Cu: Analysis of structural variants in <110> grains

The spatial ordering of helium gas bubbles (diameter ≅ 2 nm) produced in polycrystalline copper by 30 keV He+ irradiation at 300 K was studied using TEM. Transmission electron micrographs of the bubble array in <110> grains have been analysed for B along <110> in the Cu matrix. That the bubble superlattice is in the same orientation as the host metal matrix (the m orientation) has long been considered to be an important feature of bubble ordering. However, in a striking result, we have found that a high proportion of the ordered bubble array consists of structural variants which have orientations different from m. Both the spatial characteristics and frequency of occurrence of the structural variants have been determined. Examination of these features of the bubble array show considerable promise in clarifying the mechanism leading to bubble lattice formation and radiation blistering. (orig.)