A comparison between equal channel angular pressing and asymmetric rolling of silver in the severe plastic deformation regime

The structure evolution and mechanical properties of silver generated by equal channel angular pressing and by rolling and asymmetric rolling in the severe plastic deformation regime is investigated. Experimental investigations are combined with finite element analyses to improve the understanding on strain distribution developed during asymmetric rolling and to evaluate the equivalent strain accumulated after a large number of passes. The silver samples could be successfully deformed by both processing techniques up to strain values exceeding 8. The ECAP processed materials featured a submicrometer-size equiaxed grain structure with sharp grain boundaries, while symmetric and asymmetric rolling led to subgrain structures with a higher dislocation density at grain interiors and less defined grain boundaries. Accordingly, the tensile properties achieved after the different processing routes differed. In ECAP samples the strength improved at first passes and then showed a plateau for the whole range of imposed strain. In rolled silver, the achieved strength almost continuously improved even at larger strains. The finite element model showed that surface strain effects related to local friction between working rolls and sample surface regions promote an additional deformation, especially in asymmetric rolling, leading to a significant contribution at large plastic strains and generate discrepancies with equivalent strains assessed by continuum theories. (C) 2012 Elsevier B.V. All rights reserved.