High-rate deformation of nanocrystalline iron and copper

Stress–strain curves are recorded during a high-speed impact and slow loading for nanocrystalline and coarse-grained iron and copper. The strain-rate sensitivity is determined as a function of the grain size and the strain. It is shown that the well-known difference between the variations of the strain-rate sensitivity of the yield strength with the grain size in fcc and bcc metals can be extended to other strain dependences: the strain-rate sensitivity of flow stresses in iron decreases with increasing strain, and that in copper increases. This difference also manifests itself in different slopes of the dependence of the strain-rate sensitivity on the grain size when the strain changes.