Strain hardening and strain rate sensitivity of ultrafine-grained metals

The strain hardening and strain rate hardening behavior of ultrafine-grained metals at room temperature are discussed. The experimental findings obtained in our laboratory are summarized, with some recent data for ultrafine-grained Cu presented as a model case. The diminishing strain hardening capacity observed is an important factor leading to plastic instabilities, i.e., inhomogeneous and localized deformation such as necking and shear banding. The strain rate sensitivity is found to increase slightly in ultrafine-grained Cu compared with conventional Cu, but decrease in ultrafine-grained Fe and Ti relative to their coarse-grained counterparts.