Bismuth segregation in polycrystalline copper doped with about 50 at ppm bismuth was studied. A saturation value of 1-1.4 monolayer Bi enrichment could be established on the grain boundaries in the 400-700°C temperature range at a rate which increased with temperature. Further aging caused the formation and growth of grain boundary facets. The aged specimens exhibited intergranular, apparently brittle fracture. However, the fracture was always preceded by substantial plastic deformation. While the saturation value of Bi enrichment was rapidly reached at 700°C, 720°C proved to be a deembrittlement temperature. A two-dimensional phase transition may explain the sharp transition between large-scale segregation and de-segregation between 700 and 720°C.
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