Thermodynamics of interfacial segregation in metals and ceramics

A framework of our present understanding of the thermodynamics of solute segregation in metals and alloys is presented, based on the Langmuir-McLean adsorption theory and its modifications. The importance of solute-solute interactions in binary and multicomponent systems is pointed out for site competition and cosegregation. Besides the bulk activity of the solute, the key parameter for the amount of interfacial solute enrichment is the free energy of segregation, for which several predictive models based on the quasi-chemical and electronic structure approach exist. The experimental evidence of the dependence of segregation on grain boundary orientation is supported by computer modelling of the atomistic structure of grain boundaries. In ceramic materials, interfacial segregation is more difficult to interpret. Charge compensation and defect structure play an important role. The influence of segregation on materials properties is briefly discussed