MEASUREMENTS OF SELF-DIFFUSION COEFFICIENTS IN COPPER FROM ANNEALING OF VOIDS

Self-diffusion coefficients have been measured from the annealing kinetics of spherical voids in 99·999% pure copper. Thin foil specimens containing voids were annealed under conditions where it was possible for voids to shrink by the following three different diffusion mechanisms: (i) bulk diffusion; (ii) dislocation pipe diffusion in cases where a dislocation connected the void to the external foil surface; (iii) surface diffusion in cases where the void barely intersected the external foil surface. Void shrinkage was measured by transmission electron microscopy, and bulk self-diffusion coefficients were determined between 390°C and 560°C. These values, as well as high temperature tracer self-diffusivities obtained previously by standard methods, were well described by (Formula Presented) over a range of D sb values of eight orders of magnitude. The effects of fast dislocation pipe diffusion could not be detected in the temperature range 390°C to 560°C, but an upper limit to the pipe self-diffusion coefficient, at 390°C, was estimated as ∼4 × 10−13 cm2 sec−1. The surface self-diffusion coefficient was measured between 254°C and 408°C. The results were in general agreement with an extrapolation of high temperature data obtained previously from specimens in hydrogen atmospheres. The role played by surface impurities in such experiments was discussed. © 1969 Taylor & Francis Group, LLC.