Substructure Characteristics of Grain Boundary Regions and Nucleation of Recrystallisation at Grain Boundaries in High Purity Aluminium

Abstract

Boundaries existing prior to deformation are well known nucleation sites for recrystallisation. Several mechanisms have been suggested, e.g. strain induced boundary migration (SIBM) and ordinary nucleation of recrystallisation by growth of highly misoriented subgrains. The objective of the present work was to give some insight on the formation and characteristics of such boundary zones Substructure evolution nearby pre-exsisting grain boundaries was studied as a function of orientation differences or Taylor factor differences between neighbouring grains and of pre-deformation grain size, i.e., amount of shear deformation (grain boundary sliding) occuring in grain boundary areas. Slabs of high purity aluminium with different initial grain sizes were cold rolled to strains of 0.5, 1 0 and 2.0. The substructure, i.e., subgrain size and sub-boundary misorientation, were measured along grain boundaries with different orientation relationships and in the interior of the neighbouring grains. It was observed that the misorientations between subgrains were larger in the grain boundary regions than in the interior of the grains The high misorientations and high stored energy in the grain boundary regions makes them preferential as nucleation sites for recrystallised grains This was also shown indirectly by the fact that smaller initial grain size leads to smaller recrystallised grains in samples deformed to identical deformation strains.