Role of strain reversal in grain refinement by severe plastic deformation

Most of severe plastic deformation processes involve strain reversal. Till now quite big number of researches has been done on indirect study of its role, which discusses the effect of loading path in ultra-fine grained structure formation. This work is aimed to study directly the role of the strain reversal in grain refinement by severe plastic deformation. A 99.99% purity aluminum was processed by high pressure torsion up to 96° rotation (maximal equivalent strain ɛ ≈ 8) with two deformation modes: monotonic and reversal deformations with a step of 12° rotation (maximal equivalent strain ɛ ≈ 1). It was shown that strain reversal retarded the grain refinement in comparison with the monotonic deformation. This explains slower rate of the nanostructure formation of the SPD processes that involve strain reversal.