Two approaches to the study of grain boundary segregation phenomena were presented. The first was an experimental one which combined transmission electron microscopy and atom-probe field-ion microscopy in order to measure quantitatively the Gibbs interfacial excess of solute at grain boundaries whose 5 macroscopic degrees of freedom were first measured by transmission electron microscopy. By using this approach, it was possible to explore systematically the grain boundary phase space. The field-ion technique was also used to determine segregation profiles with atomic resolution. The second approach involved the Monte Carlo simulation of solute atom segregation at grain boundaries in bicrystals of single-phase face-centered cubic alloys. This approach was also used to explore grain boundary phase space systematically. The atoms were allowed to interact via long-range continuous embedded atom method potentials, and a so-called transmutational ensemble was used. The results showed that (002) twist boundaries could be enhanced in solute atoms on both sides of the phase diagram. In the case of low-angle (002) twist boundaries on one side of a certain system, the atomic sites which were enhanced in solute concentration were arranged in hourglass-like structures that were centered on the square grid of primary grain boundary dislocations. For the same boundaries on the other side of the system, the atomic sites which were enhanced in solute were located in bipyramidal regions that were based upon square cells of the same grain boundary dislocations. Thus, atomic sites that were enhanced on one side of a phase diagram were not affected on the other side, and  vice versa.

D.N.Seidman, B.W.Krakauer, D.Udler: Journal of the Physics and Chemistry of Solids, 1994, 55[10], 1035-57