| The paper analyzes mechanisms of ultra-fine grain substructure formation as observed in high pressure torsion (HPT) experiments. Accepting that HPT shearing is achieved by intergranular glide (M. Hafok and R. Pippan, Scripta Materialia, 56:757-760, 2007) the fragmentation process is interpreted within the framework of crystal plasticity. The deformation is treated as a plastic flow though the adjustable crystal lattice fragmented into misoriented regions. The basic feature of the substructure formation is an effective rotation of the slip systems approaching asymptotically the observed steady state. The fragmentation is interpreted as an instability of the homogeneous deformation mode. It is proposed that the rotation causes a continuous reconstruction of the substructure pattern. The hindered destruction of the previous pattern leads to be enhanced hardening. The size of the structural elements seems to result from the competition between two tendencies: the internal and dissipative energy tend to decrease the structural size, whereas the short-range dislocation interactions oppose this tendency. |
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