The driving forces for intergranular segregation aremuch less known than the ones for superficial segregation. Inorder to investigate the relation between grain-boundary andsurface segregation, we have calculated the segregation energyfor one impurity in both dilute limits for the Cu-Ag system. Thisis performed for the (001) surface on one hand and for thesymmetrical tilt grain boundary ?=5 (210) [001] on the other.These numerical results, obtained use N-body interatomicpotentials derived from the second moment approximation (SMA) ofthe tight-binding scheme, are then discussed within an analyticmodel, the tight-binding Ising model (TBIM). This allows us todetermine the relative role of the different driving forces insuperficial and intergranular segregation. In particularcompetition or synergy between site and size effects stronglydiffer between surface and grain-boundary segregation. Thisstudy illustrates the efficiency of the mixed SMATBIM approachto predict and to analyses interfacial segregation.
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