Grain boundary diffusion and segregation of 57Co in high-purity copper: Radiotracer measurements in B- and C-type diffusion regimes

Abstract Grain boundary diffusion of 57Co in high-purity polycrystalline copper is investigated using the radiotracer technique in Harrison's B- (850–1150 K) and C-type (550–950 K) kinetic regimes. The triple product P = s·δ·Dgb (s is the segregation factor and δ the grain boundary width) and the grain boundary diffusion coefficient Dgb of Co in Cu are determined to obey the Arrhenius laws with the activation enthalpies of Qgb = 66.2 kJ/mol and Hgb = 100.9 kJ/mol, respectively. Using the experimental estimate of δ, δ ≅ 0.5 nm, Co is found to segregate strongly at Cu grain boundaries and the corresponding segregation factor follows an Arrhenius dependence with the segregation enthalpy of Hs = −34.7 kJ/mol. Co-diffusion experiments with the 57Co and 110mAg isotopes support a ‘sub-interface’-type of grain boundary segregation of Co in Cu.