Sizes, structures and phase transformations of nano-sized thallium inclusions in aluminium

Abstract

Ion implantation of pure aluminium with thallium gives rise to the formation of nano-sized thallium inclusions due to the immiscibility of thallium in aluminium. Previous investigations have shown that the thallium inclusions can have either a fcc or a bcc structure. In this paper we report the size distribution and phases of thallium inclusions embedded in an aluminium matrix and the dependence of the size distribution and the phase on the implantation temperature. It is shown that implantations at different temperatures give rise to different sizes and phases of the thallium inclusions. Small inclusions (diameter less than about 10 nm) are almost always fcc while larger inclusions (diameter 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 temperatures in relation to the structure and size of the inclusions. Among the fcc inclusions, the smaller inclusions melt and solidify at higher temperatures than the larger inclusions. An estimate of the melting temperature of the metastable fcc 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 transformation from hcp to bcc.