3. Diffusion in relation to the geometry and intrinsic dislocations of grain boundaries

So far, we've talked about the "average" diffusivity of grain boundaries in a random polycrystal or, equivalently, that of a "random" grain boundary. However, we know that behavior varies from one joint to another.

We now focus on describing diffusion in a particular joint, characterized by its geometric parameters (disorientation and plane), which dictate the structure of the joint in terms of intrinsic dislocations. This approach provides a fairly good understanding of diffusion in joints with low disorientation angles ( $\theta <20°$ ), but this is insufficient to account for the phenomenon in wide-angle joints. Since diffusion is a property associated with the core of the joint, differences in diffusivity between grain boundaries...