THERMODYNAMICS AND STRUCTURAL ASPECTS OF GRAIN-BOUNDARY SEGREGATION

Physical and chemical properties of solid materials are strongly influenced by the chemical composition of internal interfaces. One of the crucial parameters affecting interfacial chemistry is the atomic structure of the interface. Due to its importance, a considerable amount of work was done to elucidate the relationship between structure and chemical composition of interfaces. This article reviews the present understanding of an important and fundamental part of this relationship, namely, the structural aspects of grain boundary segregation. After a brief outline of grain boundary structure and geometry, thermodynamic approaches to describe grain boundary segregation are summarized and their application to materials is discussed, covering particular sites at a single grain boundary as well as the role of interfaces in polycrystals. Both the experimental evidence of grain boundary segregation anisotropy and the theoretical results of computer simulations of grain boundary segregation are summarized. Useful methods of predicting grain boundary segregation are presented. Finally, segregation behavior of solutes at grain boundaries is compared with that at free surfaces, and examples of chemical composition of interphase boundaries are given.