Bubble structures in He⁺ irradiated metals

Abstract

Transmission electron microscopy is used to investigate the spatial arrangement of gas bubbles produced in the metals, Cu, Ni, Au, stainless steel and Ti irradiated with He⁺ at temperatures ∼ 300 K. For metals having a high degree of crystalline perfection within grains, a gas bubble superlattice is formed at high He doses in every case investigated. A study is made of the growth of bubbles on an existing superlattice (formed in a prior He⁺ irradiation) in Cu under (i) 1 MeV electron irradiation and (ii) in-situ heating in the electron microscope. The changes in bubble structure with depth in Cu for a He dose Φ near Φc (the critical dose for radiation blistering) are investigated. The development of the bubble structure and the microstructure at depths near the mean projected range is studied as a function of He dose. Electron diffraction from the super-lattice in Cu for B along <100>, <110>, <111>, <112> and <310> in the host matrix reveals some unusual but reproducible features in the diffraction pattern. An explanation is given in terms of the possible existence of patches of bubbles in which the superlattice is in a twin orientation.