MICROSTRUCTURAL EVOLUTION OF SINGLE-CRYSTALLINE AL2O3 IRRADIATED WITHSINGLE AND TRIPLE ION-BEAMS

The radiation-induced microstructural changes have been studied by cro ss-sectional transmission electron microscopy for single-crystal alpha -Al2O3 samples irradiated with triple ion beams (0.25 MeV H+, 0.6 MeV Hef and 2.4 MeV O2+: 'Triple (A)'), (0.33 MeV H+, 0.45 MeV He+ and 1.3 MeV O+; 'Triple(B)') and three consecutive single ion beams (0.3 MeV H+ ion followed by 0.6 MeV He+ and then 0.8 MeV O+ ions) at 650 degree s C to doses in the range 0.1-8.4 dpa at the damage peak. In the speci men irradiated with Triple (A), having the same average projected rang e to a total peak dose of 3.7 dpa, cavities with an average diameter o f 13 nm were formed between 1.2 and 1.75 mu m in depth causing a swell ing of 0.1% at the peak, which is larger than those of the specimens i rradiated with other conditions. The extent of the cavity-introduced r egion is some 40% smaller than observed in the damage region due to th e He+ and the O+ ions and due to the H+ ions in the sample irradiated with Triple (B). Cavities formed in the sample irradiated with H+ ion beams were found to be inhomogeneously distributed in the vicinity of dislocation loops which were grown to loop sizes up to 80 nm.