Models of Equilibrium Grain Boundary Segregation

Abstract

This chapter describes fundamentals of equilibrium grain boundary segregation. Two basic approaches to description of this phenomenon are shown – Gibbs adsorption isotherm and Langmuir–McLean type segregation isotherms. The problems with application of the latter type of the isotherm are thoroughly discussed with definition and discussion of the sets of thermodynamic variables appearing in these expressions. The danger of misinterpretation of these data is specified and accompanied by numerous examples. The Langmuir–McLean segregation isotherm is then generalised to real systems in form of the Fowler isotherm in case of binary systems and in form of the Guttmann model for multicomponent segregation. Other approaches to describe the grain boundary segregation are also shown with a special attention to the segregation at individual boundary sites. Last part is devoted to theoretical approaches to model thermodynamic functions of interfacial segregation.