Bismuth segregation at copper grain boundaries

The dependence of Bi segregation on the grain-boundary (GB) geometry for various Bi concentrations in Cu at different temperatures is investigated systematically. The GB segregation of Bi in Cu(Bi) bicrystals was determined quantitatively using energy dispersive X-ray spectroscopy (EDS) in a dedicated scanning transmission electron microscope (STEM). The Miller indices of the corresponding GB planes were determined by high resolution transmission electron microscopy (HRTEM). The energies of all experimentally investigated GBs were calculated by atomistic computer simulations. Gibbs segregation free energies were determined from the experimentally measured amount of Bi segregation using the classical McLean segregation theory. The free energies decrease monotonically with increasing calculated GB energies. The Fowler-Guggenheim segregation theory yields an attractive interaction between the segregated Bi atoms. No Bi-induced changes in the bonding at the GBs could be detected by electron energy loss spectroscopy (EELS). (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.