About Formability of Ultra-Fine Grained Metallic Materials

Abstract

Ultra-fine grained (UFG) and nanostructured metallic materials obtained via severe plastic deformation typically show very high mechanical strength but low tensile ductility, which dramatically limits their practical utility. Significant efforts were made to improve uniaxial tensile ductility of ultra-fine grained and nanostructured metallic materials. The developed strategies can be divided into two main groups. (1) The ‘mechanical’ strategies employ the mechanical characteristics of these materials, such as their work hardening ability and/or strain rate sensitivity. These mechanical characteristics can be varied via changing testing parameters, such as temperature and/or strain rate. (2) The ‘microstructural’ strategies are based on idea of intelligent microstructural design to suppress necking at early stages of plastic deformation thus improving ductility. However, not much attention was paid to the fact, that in metallforming operations, metallic materials are not deformed uniaxially, but have to undergo deformation under complex strain paths. This work aims to demonstrate that despite UFG metallic materials have low tensile ductility, they can show enhanced formability during plastic deformation in complex stress state (such as formability under biaxial stretch, which is sufficient for metalforming operations.