The results of most recent experimental, theoretical and computer simulation studies of the thermodynamics and kinetics of grain boundary and interfacial junctions (triple junctions and quadruple points) and grain boundary ridges are presented. In the first part of the presentation experimental measurements of grain boundary and interfacial triple junctions line tension are discussed. The second part of the presentation is dedicated to the application of the mentioned measurements to different capillary processes in solids. In particular, the effect of grain boundary triple junctions on the driving force for grain growth in nanocrystalline systems is considered, where it is shown that a correct examination of grain growth in nanocrystalline materials at least up to a certain mean grain size a cannot be performed if the driving force of triple junctions is not taken into account. In turn, the grain size a is determined turn by the grain boundary and triple line tension.
In spite of the fact that in the past 60 years all considerations of grain boundary motion and grain growth in solids both with immobile and mobile particles were based on the so-called Zener consideration, it is shown that the “interfacial triple line concept” changes dramatically our understanding of this phenomenon. The effect of the interfacial triple line tension on the shape of inclusions and especially on the Gibbs-Thompson relation redefines our perception of the vacancy distribution in the vicinity of a void in polycrystals and of the stability of small voids in nanocrystalline materials. Another phenomenon where triple junctions play an important role is sintering. The derived set of equations show that for high triple line energies an adhesive contact between two spherical particles does not form at all, since the expended energy of the newly created triple line cannot be compensated by the energy gain from the elimination of two free surfaces in the point of contact.
The effect of a finite triple and quadruple junction mobility on grain growth and the grain microstructure evolution in 2D and 3D systems has been studied. The results show that a finite junction mobility slows down grain boundary motion and grain growth drastically and, what is more important, changes essentially our understanding of the processes of grain growth and microstructure evolution in the polycrystals, particularly in ultra fine grained and nanocrystalline materials.