Microstructure observations for diffusion induced recrystallization and diffusion induced grain boundary migration on surfaces of zincified Cu bicrystals with [1 1 0] twist boundaries

The formation behavior of the fine-grain region alloyed with Zn due to diffusion induced recrystalization (DIR) in the Cu(Zn) system was experimentally examined for the surfaces polished in different manners using a Cu bicrystal containing a [1 1 0] twist boundary with a misorientation angle of θ = 46° zincified at 673 K for 2.88 × 10⁴ s with Cu-15 wt% Zn and Cu-30 wt% Zn alloys by a capsule zincification technique. The extent and morphology of the fine-grain DIR region vary depending on the surface conditions and the composition of the Zn-source Cu-Zn alloy. For the specimen with the surface electrolytically polished in an etchant consisting of 20 vol% of nitric acid and 80 vol% of methanol, no DIR region was formed on the whole surface when the Cu-15 wt% Zn alloy was used as a Zn source. In order to observe the morphology of the moving grain boundary owing to diffusion induced grain boundary migration (DIGM) without influences of DIR, Cu bicrystals with [1 1 0] twist boundaries of θ = 32 (Σ 27), 39 (Σ 9), 46, 51 (Σ 11) and 55° were electrolytically polished in the etchant mentioned above. The polished Cu bicrystals were zincified at 673 K for 2.88 × 10⁴ s using the Cu-15 wt% Zn alloy as a Zn source. Remarkable surface relief and clear slip bands were recognized on the surfaces due to DIGM for the specimens with the 32 (Σ 27) and 46° boundaries. The moving boundary became zigzag owing to the slip bands parallel to the moving direction. On the other hand, such surface relief and slip bands were not observed for the specimens with the 39 (Σ 9), 51 (Σ 11) and 55° boundaries. The moving boundary was considerably irregular for θ = 39° whereas rather smooth for θ = 51 (Σ 11) and 55°. The migration behavior of the grain boundary was not affected by the interruption of the zincification.