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Journal of Electron Microscopy 51:S201-S209 (2002)
© 2002 Oxford University Press

Full-length paper

Nanoscale lead-tin inclusions in aluminium

Erik Johnson1,*, Allan Johansen1, Chris Nelson2 and Ulrich Dahmen2

1Ørsted Laboratory, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark and
2National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA

To whom correspondence should be addressed. E-mail: johnson{at}fys.ku.dk

Abstract Nanoscale lead-tin alloy inclusions have been made by sequential ion implantation of lead and tin in aluminium targets at 150 and 200°C. The alloy inclusions with sizes in the range of 2–20 nm form spontaneously during the ion implantation, independent of whether lead or tin is implanted first. Alloys with nominal compositions of Pb:Sn equal to 1:1 and 1:3, respectively, have inclusion microstructures consisting of segments of a lead-rich fcc phase and a tin-rich tetragonal phase attached to each other along internal interfaces that are often close to (111)fcc. The overall morphology of the inclusions is cuboctahedral-like and most of the inclusions are bicrystalline. Some inclusions, however, have multicrystal-line morphology where one or two slabs of lead are attached between two segments of tin or vice versa, resembling a lamellar eutectic structure of nanoscale dimensions. The lead-rich fcc phase grows in parallel cube alignment with the matrix while the orientation relationship of the tin-rich phase varies. Many inclusions have the {111}Pb planes parallel to the {100}Sn planes and in this common plane both the <001>Sn and <011>Sn directions have been found to be parallel to <110>Al. Nanoprobe Energy Dispersive X-ray (EDX) analysis on the two-phase inclusions with sizes in the range of 10–20 nm shows that both phases are supersaturated, and their concentrations are considerably larger than given by the phase diagram, at around 100°C, where equilibrium can still be attained by diffusion. Inclusions less than about 5–10 nm in size nearly always display a single phase fcc structure with tin concentrations that can be as high as 50 at.%.

Keywords     Pb-Sn alloys, nanosized inclusions, extended solubility, transmission electron microscopy, Gibbs-Thomson effect, in situ melting


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