Certain thermomechanical treatments of face-centered cubic metals and alloys, with low to medium stacking-fault energies, resulted in microstructures having high fractions of Σ = 3n and other special boundaries; as defined by the coincidence-site lattice model. The interconnected networks of random boundaries were also significantly modified as a result of such processing. These modifications of the grain-boundary network were correlated with post mortem electron back-scattered diffraction and transmission electron microscopic observations of the deformed and annealed states of the material. The evolution of the microstructure to give a high fraction of Σ = 3n boundaries was related to the decomposition or dissociation of immobile boundaries during annealing. This was revealed by transmission electron microscopic observations of the decomposition of relatively immobile boundaries into 2 components; one with a very low energy (and thus immobile), and a highly mobile boundary that migrated into neighboring areas of higher strain level. The formation of low-energy grain boundaries via this mechanism, and its

effect upon boundary-network topology, was linked to known microstructural evolution mechanisms.

Microstructural Evolution during Grain Boundary Engineering of Low to Medium Stacking Fault Energy FCC Materials. M.Kumar, A.J.Schwartz, W.E.King: Acta Materialia, 2002, 50[10], 2599-612