Quantitative experiments on the transition between linear to non-linear segregation of Ag in Cu bicrystals studied by radiotracer grain on boundary diffusion

Non-linear segregation of Ag in Cu grain boundaries (GB) was quantitatively studied by radiotracer GB diffusion measurements on Cu bicrystals with non-special near 15 symmetrical [001] tilt boundaries. Bicrystals were used to guarantee a stable GB during the annealing avoiding in this way disturbing effects like GB motion etc. on the measured diffusion penetration profile. The Ag-110m radioisotope with a well-defined specific activity was applied. This allowed to determine quantitatively the amount of Ag solute atoms in a section as a function of the penetration depth. The controlled variation of the total amount of diffusing Ag atoms along the Cu GB resulted in a fundamental change of the GB penetration profile shape from almost linear to strongly curved. The curvature of the penetration profiles was unambiguously shown to be caused by non-linear segregation of Ag in Cu GB. The full Ag segregation isotherm was calculated from the corresponding GB diffusion penetration profile.