Influence of faceting-roughening on triple-junction migration in zinc

Abstract

Abstract The faceting and migration of individual triple junctions in Zn tricrystals under a constant driving force was investigated. The triple junction (TJ) was formed by three [101̅0] tilt grain boundaries (GBs) with misorientation angles θ of 43°, 37° and 6°. The stationary shape of the migrating triple junction was studied, and the migration rate was measured in-situ between 670 and 688 K using polarized light. In some experimental runs, a facet was formed on the θ = 37° [101̅0] tilt GB. This facet was parallel to the close-packed plane in the constrained coincidence site lattice (CCSL). The length of this facet decreases with increasing temperature and becomes zero at 688 K. The temperature dependence of the facet length is better described by the mean-field Andreev approximation than by the solid-on-solid model. The step energy estimated in the framework of the Bonzel approximation is about 0.1 eV/atom. In other experimental runs, the θ = 37° [101̅0] tilt GB did not facet and remained rough in the same temperature interval. This fact allowed us to compare the stationary migration of the same TJ with faceted and rough GBs. ATJ formed by faceted GBs migrates one to two orders of magnitude more slowly in comparison with a rough TJ. An unrealistically high value of the apparent migration activation enthalpy of faceted TJs can appear due to the changing geometry of faceted GBs, similar to the case of migration of faceted twin tips.