The formation of fine-grained regions alloyed with Zn, due to diffusion-induced recrystallization, was studied experimentally by examining surfaces which had been polished in various ways. Bicrystals of 15 or 30wt%Zn alloy, which contained a [110] twist boundary with a misorientation angle of 46º, were zincified (673K, 8h) by using a capsule technique. It was found that the extent and morphology of the fine-grained diffusion-induced recrystallized region varied, depending upon the surface condition and the composition of the Zn source-alloy. In the case of specimens with surfaces which had been electrolytically polished in an etchant (20vol%HNO3, 80vol%CH3OH), no diffusion-induced recrystallized region formed at the surface when a 15wt%Zn alloy was used as a source. In order to observe the morphology of a moving grain boundary which was due to diffusion-induced grain boundary migration, without interference from diffusion-induced recrystallization, bicrystals having [110] twist boundaries with Σ = 27 (32º), Σ = 9 (39º), Σ = 11 (46 or 51º) and 55º were electrolytically polished in the above etchant. The polished bicrystals were zincified (673K, 8h) by using the 15wt%Zn source. A marked surface relief, and clear slip-bands, were found on the surfaces of specimens with the Σ = 27 (32º) and 46º boundaries; due to diffusion-induced grain migration. The moving boundary became zig-zag in form, due to slip bands parallel to the direction of motion. Such surface relief or slip-bands were not observed in specimens having the Σ = 9 (39º), Σ = 11 (51º) or 55º boundaries. The moving boundary was quite irregular for the 39º boundary, but was quite smooth for the 51 and 55º boundaries. The migration behavior of the grain boundaries was not affected by interruptions in zincification.

Microstructure Observations for Diffusion Induced Recrystallization and Diffusion Induced Grain Boundary Migration on Surfaces of Zincified Cu Bicrystals with [110] Twist Boundaries. M.Moriyama, Y.Yamamoto, M.Saitoh, M.Kajihara: Interface Science, 1999, 7[2], 181-9