It was recalled that stacking-fault tetrahedra were typical vacancy clusters in face-centered cubic metals. However, stacking-fault tetrahedra had been considered to be unstable in Al because of its high stacking-fault energy; until recent observations of stacking-fault tetrahedra in thin Al foils which were subjected to tensile fracture. This confirmed that stacking-fault tetrahedra formed in Al, following irradiation with high-energy particles. In the case of electron irradiation, stacking-fault tetrahedra with an average size of 2nm formed below 203K. A higher irradiation intensity, at lower temperatures, introduced stacking-fault tetrahedra with a larger number density. Irradiation with 60keV Al+ ions introduced stacking-fault tetrahedra below room temperature, although the defect yield (ratio of number of defect clusters to number of incident ions) was about 10–3; considerably lower than that in other pure face-centered cubic metals. Following neutron irradiation below 15K, to a fluence of 2 x 1021/m2, no stacking-fault tetrahedra were observed at room temperature. Dislocation loops were observed to form and disappeared during observation using 120kV electrons that did not cause atomic displacements. Tensile fracture of Al thin foils introduced stacking-fault tetrahedra at up to 400K. This was close to the temperature at which stacking-fault tetrahedra became unstable during isochronal annealing experiments. The results suggested that a high concentration of vacancies at lower temperature tended to cause stacking-fault tetrahedra to form rather than vacancy-type dislocation loops in Al.

Formation of Stacking-Fault Tetrahedra in Aluminum Irradiated with High-Energy Particles at Low-Temperatures. Y.Satoh, T.Yoshiie, H.Mori, M.Kiritani: Physical Review B, 2004, 69[9], 094108 (11pp)