The depth distribution of bubbles and fracture in He + and D + irradiated copper

Abstract

Transmission electron microscopy is used to investigate the spatial arrangement and distribution with depth of gas bubbles produced in Cu by irradiation at 320 K to a level ~4× 10 21 30 keV He + m −2. At the depth of maximum bubble size the bubbles are random and large (up to ~10 nm across). At both shallower and greater depths the gas bubbles are smaller (~2 nm diam), much more uniform in size and ordered on an fcc superlattice with a lattice constant of a l , ~7.7 nm which (in contrast to the average bubble size) is independent of depth. It is suggested that blistering results from fracture, at a depth near the mean projected range, between large randomly-ordered bubbles which have evolved from smaller bubbles of uniform size arranged on a superlattice. For the particular case of D + irradiation of Cu at 120 K evidence is found to suggest that the fracture mechanisms involved in blistering and flaking are quite different.