Grain Boundary Diffusion of 57Co in Ultrafine Grained Niobium Processed by Severe Plastic Deformation

Abstract

Grain-boundary diffusion of Co in ultrafine-grained Nb processed by severe plastic deformation by high-pressure torsion has been studied by layer-by-layer radiometric analysis. Coefficients of grain-boundary diffusion for several temperatures have been determined. It is shown that diffusion along grain boundaries proceeds much faster than in coarse-grained niobium with relaxed boundaries, which is explained by the formation of "non-equilibrium" grain boundaries under the severe plastic deformation, which are the paths of ultrafast diffusion. Recovery processes occur in non-equilibrium grain boundaries under heating, due to which their properties approach to those of conventional high-angle boundaries in the coarse-grained material.