Determination of activation volume in nanocrystalline Cu using the shear punch test

Based on a comparison with tensile tests, the results reported here show that the stress relaxation method can be used with the shear punch test (SPT) to obtain the physical activation volume V* for nanocrystalline metals as well as on small scale samples whose size range may be in the order of few millimeters. This provides a useful alternative to tensile tests when sample sizes are small or tensile ductility is limited. The SPT stress relaxation method gave expected trends for changes in the apparent activation volume as a function of stress in several coarse grain metals and alloys. The physical activation volume V* ≈ 20 b3 for the 50 nm grain size electroplate nanocrystalline Cu. This indicates that dislocation slip rather than diffusion-controlled mechanisms (V* ≈ b3) dominate the plasticity, as might be anticipated for this grain size. Both the apparent and physical activation volumes showed a decrease with increasing stress level that suggests an influence of strain hardening on the dislocation mobility at this grain size. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.