Peculiarities of Fe and Ni Diffusion in Polycrystalline Cu

The peculiarities of Ni and Fe diffusion in polycrystalline Cu and Cu-Fe alloys at a 650-750 °C temperature range were studied. It was shown that the bulk diffusion coefficients were in a good agreement with the available literature data obtained for different temperature concentration ranges. The obtained values of the Ni GB diffusion triple product could be described as sδDb=8.8×10-13×exp(-165 kJmol-1RT)m3s-1. The obtained values were an order of magnitude less than the values obtained by the radiotracer method. This fact was explained by the negative segregation of Ni at the Cu GB. A stronger negative segregation of Fe in the copper GB reduced the penetration depth of iron along the GB because of an additional (negative) "driving" force; this explained why there was no advanced grain boundary diffusion. Another peculiarity of the Fe diffusion that was confirmed was the significant supersaturation of the Cu-based solid solution near the Fe/Cu interface.