The effect of relative crystal and boundary orientations on grain boundary diffusion rates

Abstract

The rate of self-diffusion of silver in the grain boundaries of bicrystals, misoriented by rotations of θ around a [100] axis, has been measured for 9° ⪕ θ ⪕ 28°. Within the experimental uncertainty, the results can be described, using the dislocation model of grain boundaries, with the assumption that the coefficient of self-diffusion, D p , in grain boundary dislocation pipes is independent of θ (for θ ≲ 28°) and that D p is several orders of magnitude larger than the lattice self-diffusion coefficient, D L (at 500°C, D p ~ 4 × 10 6 D L ). The dependence of D p on T is given by: D p = 0.14 exp [ −19,700 RT ] cm 2 sec −1 . The activation energy (19.7 ± 2 kcal/gm atom) for D p is in good agreement with that (20 ± 2 kcal/gm atom) reported earlier for self-diffusion in grain boundaries separating randomly oriented crystals. A marked effect of grain boundary orientation on the diffusion penetration was observed for θ = 9°.