Helium gas bubble lattices in face-centred-cubic metals

Abstract

ION irradiation of metals with helium or hydrogen isotopes commonly results in the formation of microscopic gas bubbles. At very high doses, radiation blistering and related phenomena can cause severe damage to surfaces¹. Much research has been stimulated by the need to find materials with acceptable erosion and gas loading properties for use in future controlled thermonuclear reactors. Bubble formation is also important in fission-reactor fuel technology and other applications^2,3. The underlying bubble structure of face-centred-cubic (f.c.c.) metals has remained largely unknown, although much has been done on depth profiling light gases implanted to high doses (see, for example, refs 3–5). Inert-gas bubbles lying on a space lattice have been reported previously only for the body-centred-cubic (b.c.c.) metal molybdenum^6,7. There have been many observations, mainly for b.c.c. metals, of the similar ordering of voids produced by particle irradiation^8,9. The void lattice spacing is typically 5–10 times that found for bubbles (∼5 nm). We report here on the bubbles produced in several f.c.c. metals by 30 keV helium-ion irradiation to a level just below the critical dose for blistering. A new result for this important class of metals is that the helium gas bubbles lie on a superlattice having an f.c.c. structure with principal axes aligned with those of the matrix.