PATTERNS IN HEAVILY DEFORMED METALS

Ductile metals can sustain very high levels of plastic strain without fracture. At low or intermediate temperatures (deformation regime dominated by crystallographic slip), deformation is accompanied by an increasing storage of dislocation density concomitant with a strength rise that can amount to more than two orders of magnitude. Dislocations accumulate in characteristic heterogeneous cellular patterns whose average size correlates with the interdislocation distance and with the inverse of the strength. The patterns do not merely shrink as deformation proceeds but suffer qualitative changes attested by a marked transition in work hardening behaviour. Although the starting cellular dislocation substructure, composed of thick, tangled walls is progressively substituted by a neat arrangement of two-dimensional sub-boundaries, the work hardening transition observed at large strains does not coincide with any sudden cell to subgrain substructural transition and its underlying substructural basis has not yet been unveiled. This and other unsolved questions about the substructures of heavily deformed metals will be addressed in the paper, namely the qualitative and quantitative observation of self-similarity of the substructures in a limited scale-range and its implications in the discussion on the physical process of substructure building.