| Grain boundary segregation and embrittlement in a number of systems has been investigated using analytical electron microscopy (AEM) techniques. Segregation to grain boundaries has been observed using X-ray energy dispersive spectroscopy (XEDS) with an unprecedented spatial resolution and sensitivity. 2D X-ray mapping of compositional distributions has been shown to be applicable to the case of equilibrium segregation and such maps contain the same information as can be obtained with other, more traditional, approaches. In addition to studies of the embrittling systems S-doped Ni and Bi- and Sb-doped Cu, Ag, which does not embrittle, has been observed at grain boundaries in Cu, the first direct measurement of Ag segregation in Cu.; Changes in the electronic structure, and hence bonding, at the grain boundaries in the presence of the segregants has been examined using the electron energy loss near edge structure (ELNES). In the embrittling systems of S-doped Ni and Sb-doped Cu, extra intensity in the ionization edge, just above the edge onset, was observed and is consistent with earlier measurements on Bi-doped Cu. No effect was seen with segregation of the non-embrittling Ag. The embrittling impurities are believed to reduce cohesion at the grain boundaries by changing the shape of the d-band, through bond rehybridization, and it is this change in shape that is observed as the extra intensity in the ELNES. |
