BISMUTH SEGREGATION AT COPPER GRAIN BOUNDARIES

摘要

The dependence of Bi segregation on the grain-boundary (GB) geometry for various Bi concen- trations 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 exper- imentally investigated GBs were calculated by atomistic computer simulations. Gibbs segregation free ener- gies 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 ener- gies. 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 spec- troscopy (EELS).