How to compare superficial and intergranular segregation? A new analysis within the mixed SMA–TBIM approach

Abstract

The driving forces for intergranular segregation are much less known than the ones for superficial segregation. In order to investigate the relation between grain-boundary and surface segregation, we have calculated the segregation energy for one impurity in both dilute limits for the Cu–Ag system. This is performed for the (001) surface on one hand and for the symmetrical tilt grain boundary Σ=5 (210) [001] on the other. These numerical results, obtained using N-body interatomic potentials derived from the second moment approximation (SMA) of the tight-binding scheme, are then discussed within an analytic model, the tight-binding Ising model (TBIM). This allows us to determine the relative role of the different driving forces in superficial and intergranular segregation. In particular competition or synergy between site and size effects strongly differ between surface and grain-boundary segregation. This study illustrates the efficiency of the mixed SMA–TBIM approach to predict and to analyse interfacial segregation.