Grain boundary self- and solute diffusion and segregation in general large angle grain boundaries in copper

The temperature dependence of solute grain boundary (GB) diffusion of Se, Sb, and Au iu general large angle GBs of Cu (polycrystals) was investigated by the radiotracer serial sectioning technique using Se-75, Sb-124 and Au-195 radioisotopes. Furthermore, applying the radioisotope Cu-64 GB selfdiffusion in Cu was measured for the first time directly. All tracer measurements were carried out in Harrison's type-B kinetic regime, and the parameter P = s delta D-GB was determined in dependence on temperature; s = c(GB)(solute)/ c(V)(solute) being the GB segregation factor of the solutes (s=1 for the self- diffusion), delta (= 0.5nm) the GB width and D-GB the GB diffusion coefficient. Using Cu material of different bulk purity a significant decrease of GB self-diffusion with increasing impurity content was observed, Furthermore D-GB values of Au and Se were directly determined in the type C kinetic regime, revealing a slightly reduced GB solute diffusivity in comparison to the Cu solvent diffusivity. Both phenomena can be explained in terms of solute - solvent chemical interactions, leading to immobile precursors of precipitates of a 2D phase [1].