The steady-state migration of triple junctions in tricrystals with impurities which segregated strongly at the grain boundaries was considered. When the mobility of impurities within grain boundaries was much higher than the rate of impurity-atom jumps from the grain boundary to the bulk, triple-junction migration caused a divergence of the impurity content at the triple point. It was shown that this divergence could be relaxed by non-equilibrium segregation at the growing grain boundary, or by the formation of an inclusion of the impurity-rich phase at the triple point. In the former case, the dihedral angle at the triple-point differed considerably from its equilibrium value and was strongly temperature-dependent. The triple junction could not be described as being an individual object with its own mobility. In the case of cavity formation at the triple point, the triple junction could be characterized by its own mobility. It was shown that the dependence of the triple-junction migration rate upon the driving force was approximately linear at low migration rates, and highly non-linear at high migration rates. There was also a maximum possible steady-state migration rate of the triple-junction/inclusion system. At higher migration rates, jerky motion of the triple-junction occurred. Both models were in good agreement with experimental data.

Theory of Triple Junctions Mobility in Crystals with Impurities. E.Rabkin: Interface Science, 1999, 7[3-4], 297-305