Diffusion along grain boundaries (GBs) often controls the evolution of
structure and properties of engineering materials at elevated tempera
tures. A knowledge of diffusion characteristics of GBs and deep fundam
ental understanding of this phenomenon are critical to many materials
applications. The purpose of the present review is twofold. First, a c
omprehensive overview of boundary diffusion theory with emphasis on th
e interpretation of concentration profiles measured in diffusion exper
iments is given. The most important situations encountered in boundary
diffusion experiments are considered, such as diffusion in the B and
C regimes, diffusion in the presence of segregation, diffusion in mult
iple GBs, diffusion in moving GBs, etc. The discussion of such situati
ons is accompanied by easy to use recipes for the determination of bou
ndary diffusion characteristics from the concentration profiles. Secon
d, the most recent advances in the basic understanding of GB diffusion
are reviewed. The focus is placed on diffusion-segregation effects, d
iffusion in polycrystals with moving GBs, diffusion in oriented bicrys
tals, and other areas of increased research activity. Recent progress
in the atomistic interpretation of GB diffusion is also discussed. It
is demonstrated that many problems in the area can only be solved by t
he combination of new theoretical models with precise measurements usi
ng novel experimental techniques; and that diffusion measurements can
be used as a tool to study the structure and physical properties of GB
s. (C) 1997 The Institute of Materials and ASM international.