Grain boundary diffusion of 59Fe in high-purity copper

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Grain boundary diffusion of iron in high purity polycrystalline copper is measured using the radiotracer technique and applying the 59Fe isotope. At lower temperatures, T<949 K, the measurements are performed under Harrison's C-type kinetic regime and the grain boundary diffusion coefficient of Fe in Cu, Dgb, is determined, Dgb=5.6⋅10−6×exp(−121kJmol−1/RT) m2/s. Unconventional penetration profiles are measured for Fe grain boundary diffusion in Cu at higher temperatures (≥ 949 K) under the intended B-type kinetic regime, in fact formal C-type profiles are systematically observed instead. Molecular dynamics simulation with the literature Finnis-Sinclair type interatomic potentials [Ackland et al., Phil. Mag. A, 1997] discovered an unexpected response of Cu grain boundaries on a partial Fe coverage at temperatures above 900 K. A model of Fe penetration in polycrystalline Cu in such conditions is proposed, which explains the untypical shape of the penetration profiles. The combination of the B- and C-type grain boundary diffusion measurements predict a strong segregation of Fe in Cu with a low segregation enthalpy.