GRAIN-BOUNDARY FACETING IN CU-BI ALLOYS

Observations on an embrittled Cu 0.0115 wt% Bi alloy in the electron microscope have shown that grain boundaries in this material exhibit very marked faceting. This faceting cannot be explained by the geometrical requirements of the coincidence site lattice. Boundaries in embrittled Cu- Sb alloys do not show such faceting. A theoretical model is given to investigate the conditions for facet stability in the presence of segregated atoms. A study has also been made of the nature of fracture paths in these alloys. There are two possible modes of fracture: the first is transgranular and is accompanied by significant plastic deformation: in the second mode, fracture accurately follows the facets of the boundary and there is no evidence of accompanying plastic deformation. © 1979.