Pseudo type-B diffusion regime in Cu grain boundaries below 250 °C

We have extended grain boundary diffusion measurements in polycrystalline Cu specimens down to 100°C which have been earlier considered impossible to perform. Apparently, diffusion in the sub grains hypothesized to be present within the large grains, made these measurements possible. Interaction of diffusion fields in the normal grain boundaries and in the sub grains resulted in tracer profiles which followed Whipple-Suzuoka type of kinetics despite total absence of diffusion in the lattice. Hence, these measurements are termed to have been made in Pseudo Type-B kinetic regime. After accounting for diffusion in the sub grains, it was possible to obtain grain boundary diffusion coefficients which agreed well with the extrapolated values of the earlier high temperature measurements. All the available data in polycrystalline Cu can now be described by δDb = 2.9×10-9 exp ( - 0.95eV/kT) cm3/sec.