On the nucleation of recrystallised grains from grain boundary regions

Particle stimulated nucleation (PSN) is often assumed to be the dominating mechanisms for the nucleation of recrystallised grains in materials that contain large second phase particles. After hot deformation, however, where the formation of deformation zones around particles is retarded due to recovery, other mechanisms like nucleation from grain boundaries presumably become increasingly important. The objective of the present work was to study the competition between PSN and nucleation from grain boundary regions after various deformation conditions. This was performed by an experimental set-up where particle size distributions and the amount of grain boundary surface (determined by strain and initial grain size) were varied. The results demonstrated that the nucleation from grain boundary regions provided a significant contribution, especially after hot deformation. Since the texture had a high random contribution even in the cases where PSN was weak, it is suggested that the nucleation of randomly oriented grains can take place in the transition zones (boundary regions) between the stable deformation texture components. These zones might obtain a random character due to large lattice rotations that frequently appear for compatibility reasons. (au) 12 refs