The role of crystallographic texture on mechanically induced grain boundary migration

Abstract

Mechanically induced migration of grain boundaries and triple junctions not only determines the size and shape of nanostructures created by severe plastic deformation, it substantially affects their mechanical properties as well. Grain growth during deformation of nanostructures has been widely observed. As the nanostructures processed by severe plastic deformation are a consequence of a dynamic equilibrium between refinement and local mechanically induced coarsening, it is widely accepted that such nanostructures would remain stable upon further loading. However, pronounced grain coarsening can be observed when pure UFG copper prepared by high pressure torsion (HPT) is additionally cold rolled. The coarsening continues up to rolling strains, ε = 1, i.e. until favourable grain orientations for rolling are developed. For larger strains subsequent refinement to minimum boundary spacing identical to the HPT microstructure is observed. Interestingly, less grain growth is observed for two other sample orientations of the HPT microstructure which are rolled along different directions with respect to the sample coordinate frame. Crystallographic texture of these samples were favourable with respect to the new strain path, highlighting its role for mechanically induced growth and suggesting a distinct influence of grain orientation on the mechanically induced coarsening process.