Abstract
Ti-tritides containing about 10% (H/M) tritium were aged at 300 and 550[ddot]C for several weeks and then inspected for 3He bubble formation by transmission electron microscopy. Micrographs of α-phase regions aged at 300[ddot]C displayed platelike He precipitates on (0001) habit planes accompanied by very strong contrast. Plates of the δ-tritide which were also present during ageing showed the usual bubble structure, somewhat coarser than at ambient temperature, α-phase regions aged at 550[ddot]C were found to contain a significantly reduced number density of rather large faceted bubbles. The present and previous results are interpreted in the light of the current understanding of He bubble formation in metals. The difference in the bubble morphology at different temperatures is attributed to differences in the availability of thermal vacancies during He clustering. Evidence is provided that up to about 600 K, He atoms diffuse interstitially and form interstitial clusters whereas at higher temperatures He diffusion and clustering is increasingly affected by the rising vacancy concentration. The results for high temperatures are consistent with 4He desorption measurements after room temperature 4He ion implantation into α-Ti.