SIZES, STRUCTURES AND PHASE-TRANSFORMATIONS OF NANO-SIZED THALLIUM INCLUSIONS IN ALUMINUM

Ion implantation of pure aluminium with thallium gives rise to the for mation of nano-sized thallium inclusions due to the immiscibility of t hallium in aluminium. Previous investigations have shown that the thal lium inclusions can have either a fee or a bcc structure. In this pape r we report the size distribution and phases of thallium inclusions em bedded in an aluminium matrix and the dependence of the size distribut ion and the phase on the implantation temperature. It is shown that im plantations at different temperatures give rise to different sizes and phases of the thallium inclusions. Small inclusions (diameter less th an about 10 nm) are almost always fee while larger inclusions (diamete r larger than about 10 nm), formed at higher implantation temperatures , usually are bcc, but hcp inclusions are also seen. Also presented in this paper are some results on the melting and solidification tempera tures in relation to the structure and size of the inclusions. Among t he fee inclusions, the smaller inclusions melt and solidify at higher temperatures than the larger inclusions. An estimate of the melting te mperature of the metastable fee thallium phase at low pressures (P < 1 GPa) is 540 K. Finally, in-situ heating sequences show various solid- state phase transformations, with the most prominent being the transfo rmation from hcp to bcc.