Interfacial segregation in Ag-Au, Au-Pd, and Cu-Ni alloys: II. [001] Σ5 twist grain boundaries

Abstract

Atomistic simulations of segregation to [001] Σ5 twist boundaries in Cu−Ni, Au−Pd, and Ag−Au alloy systems have been performed for a wide range of temperatures and compositions within the solid solution region of these alloy phase diagrams. In addition to the grain boundary segregation profiles, grain boundary free energies, enthalpies, and entropies were determined. These simulations were performed within the framework of the free energy simulation method, in which an approximate free energy functional is minimized with respect to atomic coordinates and atomic site occupation. For all alloy bulk compositions (0.05 ≤ C ≤ 0.95) and temperatures (400 ≤ T (K) ≤ 1,100) examined, Cu and Au segregates to the boundary in the Cu−Ni and Au−Pd alloy systems, respectively; although in the Ag−Au alloys, the majority element segregates to the boundary. The width of the segregation profile is limited to approximately three to four (002) atomic planes. The classical theories for the segregation, and the effects of the relaxation with respect to either the atomic positions or the atomic concentrations, are discussed. The boundary thermodynamic properties depend sensitively on the magnitude of the boundary segregation, and some of them are shown to vary linearly with the magnitude of the grain boundary segregation.