Strain hardening behaviour and deformation kinetics of Cu deformed by equal channel angular extrusion from 1 to 16 passes

The work hardening rate, strain rate sensitivity and the apparent activation volume of copper processed by equal channel angular extrusion (ECAE) for 1-16 passes are investigated. Constant strain rate and strain rate jump tests performed in compression up to 30% of strain reveal stage III and IV work hardening for specimens subjected to less than 4 passes of ECAE, while specimens subjected to more than 4 passes show the additional occurrence of stage V work hardening. The length scale deduced from activation volume measurements corresponds with the distance of dislocations measured within dislocation walls. This suggests that the rate-controlling mechanism is the interaction of lattice dislocations with dislocations in the cell walls or subgrain boundaries and/or the mutual interaction of cell wall/subgrain dislocations. A hyperbolic function accounting for the rate-controlling deformation mechanism is proposed in order to account for the possibility of backwards fluctuations within the cell walls. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.