Diffusion in Grain Boundaries and Their Structure

Abstract

In order to gain an insight into the structure and properties of grain boundaries, diffusion along grain boundaries has been studied as a function of relative orientation of the grains and of the boundary. Experiments were made by comparing the depth of penetration of silver along the boundaries of columnar copper in the columnar direction [100]. The results indicate that, for angles of misfit between the grains, greater than 20° and smaller than 70°, diffusion along grain boundaries is greater than volume diffusion (near 700°C) and reaches a maximum around 45°. Outside of that range of relative orientation the rate of grain boundary diffusion is not greater than volume diffusion. These results are correlated with the information available about the energy of grain boundaries, and it is concluded that at small angles the dislocation model of grain boundaries describe satisfactorily the situation, while at larger angles the grain boundaries are better described in terms of areas of fit and misfit.