Diffusion-induced grain boundary migration was studied in the Cu–Zn system by exposing polycrystalline Cu to Zn vapour with a Cu-38wt%Zn alloy as the source of Zn. The time and temperature dependence of the migration distance was studied at 350 to 600C. The composition-distance profile was obtained along the thickness of the sheet specimen to determine the diffusivity, kDbδ at each temperature. Similarly, the quantity of Zn was determined behind the migrated grain boundary to calculate the coherency strain energy and the total chemical free energy change. It was observed that a part of the total free energy change was used for volume diffusion ahead of the migrating grain boundary. The effective free energy change was calculated and it was observed that the fraction of the total free energy change used for volume diffusion increased as the transformation temperature increased. A plot of instantaneous rate of migration vs. composition behind the grain boundary has indicated that the coherency strain energy acted as the driving force for diffusion induced grain boundary migration. The fine-grained layer followed a parabolic growth behavior. The diffusion coefficients calculated from the thickness of the fine-grained layer were of the same order of magnitude as those calculated from the rate of migration of the grain boundary. The diffusivity as well as the activation energy calculated from the kDbδ versus 1/T plot corresponds to that of grain boundary diffusion of Zn in Cu.

Diffusion Induced Grain Boundary Migration in the Cu–Zn System. B.Sivaiah, S.P.Gupta: Materials Characterization, 2008, 59[9], 1141-51