Grain boundary diffusion and segregation of Ge in Cu: Radiotracer measurements in different kinetic regimes

Abstract

Abstract Grain boundary (GB) solute diffusion of Ge in Cu polycrystals was systematically investigated by the radiotracer serial sectioning technique using 68Ge and 71Ge isotopes. The diffusion measurements were carried out under conditions of Harrison’s B- (923–626 K) and C- (576–451 K) type diffusion regimes. In the B-type diffusion regime, the triple product P = s δ D gb (s is the segregation factor and δ the GB width) was found to follow the Arrhenius law P = 4:0 × 10-16 × exp(-58.6 kJ mol-1/RTÞ m3s-1, where R is the universal gas constant and T the temperature. Measurements in the C-regime directly yielded the GB diffusion coefficient D gb, D gb = 2.8 × 10-6 × exp(-84.8 kJ mol-1/RTÞ m2s-1. Combining the obtained P and D gb values and assuming δ ≌ 5 × 10-10 m, the GB segregation factor for Ge in Cu was determined to follow an Arrhenius dependence s = 0.29 exp(26 kJmol-1/RTÞ. The determined segregation coefficients s are discussed together with previous results on solute segregation in Cu and Ag, and it is concluded that the well-known Hondros relation, which relates segregation and bulk solute solubility, can generally be used only for a qualitative estimation of the segregation ability. Furthermore, the obtained results for the triple product s δ D gb and the directly measured D gb values are discussed in relation to previous GB diffusion measurements of some other solutes in Cu and Ag in the B- and C-regimes.