Mechanism of Hardening of Ultrafine-Grained Aluminum after Annealing

A theoretical model is proposed that describes the hardening mechanism of ultrafine-grained aluminum obtained by high pressure torsion after low-temperature annealing. Within this model, the hardening is due to the successive transformation of the grain-boundary dislocation structure. In particular, plastic deformation is occurs through the emission of lattice dislocations from triple junctions of grain boundaries containing pile-ups of grain-boundary dislocations, the subsequent sliding of lattice dislocations in the grain body, and the formation of walls of climbing grain-boundary dislocations along opposite grain boundaries. The energy characteristics and critical stresses for emission of lattice dislocations are calculated. Theoretical dependences of the flow stress on the plastic strain, which demonstrate good qualitative and quantitative agreement with experimental data, are constructed.