Local texture-microstructure correlation due to deformation localization in ECAP-processed nickel

Abstract

A correlation between the local microstructure and texture is investigated in ultrafine grained nickel of 99.6wt% purity deformed via Equal Channel Angular Pressing (ECAP). Annealing at 700K induces discontinuous recrystallization and a layered microstructure with alternating recrystallized coarse- and remaining ultrafine grained areas is formed. A large scale analysis of as-deformed Ni applying orientation-imaging microscopy revealed local texture variations on a similar scale. The shear band formation via plastic flow localization induces systematic variations of local texture and microstructure which affects subsequent recrystallization. The correlation of fiber components of the shear texture and the spatial distribution of specific orientations before and after annealing allows to identify regions of decreased thermal stability. The dominant texture feature after annealing is found to be a prominent rotated cube component, which is a consequence of nucleation and growth of new grains on the cost of the defected microstructure during recrystallization. The formation of the observed anisotropy as a consequence of the heterogeneous distribution of crystal orientations is discussed within the context of dynamic recrystallization, plastic instabilities, stored energy and recrystallization nucleation mechanisms.