Stresses and deformation at grain boundaries

Source abstract

Abstract Grain boundary sliding is frequently observed during the creep of polycrystals and this can alter both the internal stresses and the creep rate. Sliding arises because the shear and normal forces acting on the grain boundaries can be relaxed by separate mechanisms at different rates. If sliding is easy the shear forces can in the limit tend to zero. The normal forces are then relaxed more slowly by plastic deformation inside the grain or by diffusion creep. While the former distorts the interior of the grain the latter does not. Several two dimensional models of the diffusion mechanism have appeared in which rigid slabs slide past each other. Diffusion plates out material on the boundaries and controls grain movement normal to the boundary. It is also possible to solve the ‘rigid grain’ situation in three dimensions when rapid diffusion at boundaries relaxes the normal forces. The shear process then controls the grain motion and it is necessary that the grains roll over each other.