The effect of pressure on indium diffusion along ⟨001⟩ tilt grain boundaries in copper bicrystals

The effect of pressure on the diffusion of indium along two grain boundaries (GBs) in copper bicrystals has been investigated. The GBs studied were of symmetrical tilt type with a [001] misorientation axis. The tilt angle of one GB was 36.5 degrees, which corresponds to the near Sigma 5 coincidence orientation, where Sigma is the inverse density of the coincidence sites in the two misoriented crystal lattices. The other GB was a general boundary with a tilt angle of 45 degrees. The diffusion along the [001] tilt axis has taken place at the temperature of 923 K and under argon gas pressures up to 1 Ga. The following activation volumes have been found: 0.94 +/- 0.11 Omega(Cu) for bulk diffusion, -0.5 +/- 0.7 Omega(Cu) for the diffusivity of the near Sigma 5 GB and -0.6 +/- 0.3 Omega(Cu), for the diffusivity of the 45 degrees [100] GB, where Be, is the atomic volume of copper. Two interpretations of this result seem plausible. The first interpretation is that the In atoms diffuse along the [001] tilt axis by an instertitialcy mechanism. It is known that for such a diffusion mechanism the activation volume is close to zero. The alternative explanation bases on the observation that the parameter measured is the GB diffusivity, which depends on the product of the GB diffusion coefficient and the segregation factor. An enhancement of the In segregation under pressure would lead to an increase of the GB diffusivity. It seems plausible that both interpretations are true and the fact that the atomic volume of In is a factor of 2.2 larger than that of Cu plays an important role both for the increased segregation of In under pressure and the diffusion mechanism.