Strain hardening, strain rate sensitivity, and ductility of nanostructured metals

This paper presents an overview of the strain hardening and strain rate hardening behavior of nanostructured and ultrafine-grained metals. The experimental findings obtained in our laboratory are summarized, with some recent data for ultrafine-grained Cu presented as a model case. Due to the diminishing strain hardening capacity and inadequate strain rate hardening, plastic instabilities in the form of inhomogeneous and localized deformation such as necking and shear banding often contribute to the low ductility of nanostructured and ultrafine-grained metals at room temperature (RT). The observed grain size dependence of the strain rate sensitivity is also discussed in terms of its implications for new deformation mechanisms when the grain size is in the nanocrystalline (nc) and ultrafine regime.