Ag grain boundary diffusion and segregation in Cu: Measurements in the types B and C diffusion regimes Original Research Article

Grain boundary (GB) diffusion of 110mAg in polycrystalline Cu was measured under the conditions of the Harrinsonʹs type B (962–675 K) and type C (565–452 K) diffusion regimes. In the B-type diffusion regime, the triple product P=sδDgb (s is the segregation factor and δ the GB width) was found to follow the Arrhenius law P=(1.4+0.6−0.4)·10−15·exp{−[(69.1±2.5)kJ·mol−1]/RT} m3 s−1. The measurements under the C regime conditions directly established the temperature dependence of the GB diffusion coefficient Dgb, Dgb=(1.7+0.7−0.5)·10−4·exp{−[(108.6±1.9)kJ·mol−1]/RT} m2 s−1. Combining both results and assuming as usual δ≅5·10−10 m the segregation factor s was determined to follow an Arrhenius dependence s=s0 exp(−Hs/RT) with the pre-exponential factor s0=(1.6+1.4−1.0)·10−2 and the segregation enthalpy Hs=−39.5±4.0 kJ·mol−1. Experimental conditions were analyzed to figure the factors resulting in the curvature of the radiotracer profiles. Probable non-linear segregation was shown to give only marginal (if any) effect. The initial parts of the profiles are well described by accounting for the GB motion during diffusion anneal. The analysis shows that a hypothetial dislocation-enhanced volume diffusion at low temperatures cannot disturb the C-regime conditions in the present experiments. The very small tracer concentrations applied in the types B and C diffusion measurements indeed allow us to establish equilibrium GB segregation at negligible concentrations of solute atoms. The results are compared with the available literature data obtained by direct measurements with non-negligible solute concentrations.