Diffusion-induced grain boundary migration and associated concentration profiles in a CuZn alloy

Abstract

Diffusion-induced grain boundary migration (DIGM) and diffusion-induced recrystallization (DIR) with their associated concentration profiles occurring in a CuZn alloy have been studied by Electron Probe Micro Analysis and Analytical Electron Microscopy. Both DIGM and DIR occurred in Cu when Zn was diffused in along the grain boundaries at 480 and 400°C. The Zn concentration was high in DIR regions (2−~20% Zn) and low in DIGM regions (<2%). There are two topologically different DIGM types, showing a smooth (Type I) or a rough (Type II) surface upon etching. The Zn concentration is lower in Type I than that in Type II. There is a sudden drop in Zn concentration across the grain boundary in Type I, while in the case of Type II there is a concentration trough immediately in front of the final position of the boundary. It was concluded that the rough area is due to an oscillatory migration. The more frequently the boundary has oscillated, the higher the Zn concentration in this area. The DIR zones also exhibit concentration troughs across the boundaries between adjacent grains. Based on the similarity between the concentration profiles exhibited in the Type II DIGM areas and in DIR areas, it was postulated that the growth of the DIR grains after its nucleation may be explained by the same mechanism as the migration of the boundaries in DIGM Type II.