Kinetics of diffusion induced grain boundary migration of [100] twist boundaries in the Cu(Zn) system

The kinetics of diffusion induced grain boundary migration (DIGM) in the Cu(Zn) system was experimentally studied for [100] twist boundaries using Cu bicrystals annealed at 693 K for various times between 5.4 × 10⁴ and 1.73 × 10⁵ s. The experiment was carried out for bicrystal specimens with misorientation angles of 15, 20, 23 (∑13), 25, 28 (∑17), 32, 37 (∑5), 40, 44 (∑29) and 45°. During DIGM, the grain boundary migrates rather unidirectionally towards one of the crystal grains for most of the specimens and becomes wavy with increasing annealing time. The migration distance at 5.4 × 10⁴ s is smaller for coincidence site lattice (CSL) boundaries with low energy than for random boundaries with high energy. The migration rate of the moving boundary was observed to be almost constant independent of the annealing time between 5.4 × 10⁴ and 1.73 × 10⁵ s. The steady state migration rate is larger for low-energy CSL boundaries than for high-energy random boundaries. The experimental results were quantitatively analyzed using the energy balance model proposed by Kajihara and Gust. In this analysis, the effective driving force for DIGM was calculated as a function of the migration rate. The calculation indicates that 75-93% of the chemical driving force is consumed by the volume diffusion of Zn in the untransformed Cu matrix ahead of the moving boundary under the given experimental conditions. Considering the energy consumption, the mobility M of the moving boundary was evaluated for the steady state stage. The evaluation yields M = 6.6 × 10^-17 m⁴/J s as the mobility of the random boundary for DIGM in the Cu(Zn) system at 693 K.