Abstract
Cu bicrystals with a ∑ = 19a {331} grain boundary, grown by the Bridgman technique, have been doped with 14, 24, 25 and 64 at.ppm Bi. After annealing between 500 and 800°C the segregation was quantified using energy-dispersive X-ray spectroscopy in a dedicated scanning transmission electron microscope. Grain-boundary faceting on low-index planes was observed and the segregation level was significantly higher at the facets than at the non-faceted segments. The fraction of faceted grain boundaries was found to increase with increasing annealing temperature, implying that the faceting transition is thermally activated. Only the completely faceted grain boundary exhibits brittle behaviour. Faceting appears to be a necessary prerequisite for grain-boundary embrittlement of the ∑ = 19a, {331} grain boundary, possibly because it allows more Bi atoms to be incorporated at the boundary. It is suggested that this embrittling mechanism may be a general phenomenon in Bi-doped Cu.
