Nanostructured Cu-Bi alloys prepared by co-evaporation in a continuous gas flow

A new preparation process for nanostructured alloys utilizing co-evaporation in a continuous gas flow has been developed. Inert gas is injected into a preparation chamber through a nozzle in order to establish a convectional flow that carries crystallites of one element above an evaporation source of a second element so that the atoms of the second source condense at the crystallite's surfaces in the form of a thin coating. In this manner Cu crystallites were coated with Bi, resulting in Bi-doped grain boundaries after consolidation of the Bi-coated Cu crystallites. The maximum overall concentration of Bi without formation of crystalline Bi was 10 at.%, corresponding to one monolayer of Bi atoms distributed along the grain boundaries. The average grain size in the consolidated samples was found to depend on the Bi concentration. Annealing experiments showed that the onset of grain growth was shifted to higher temperature for Bi-doped samples.