Ductility by Shear Band Delocalization in the Nano-Layer of Gradient Structure

Abstract

Nanostructured metals typically fail soon after yielding, starting with the formation of narrow shear band. This chapter reports the observation of shear band delocalization in gradient metals. Ductility is generally defined as uniform elongation in the specimen gage length during tensile testing. It is found that shear bands were formed in the NS layers at very early stage during tensile testing, as nanostructured (NS) metals typically do. Unexpectedly, the shear bands became stabilized due to strain gradient and propagated slowly along the gage length to become a localized strain zone (LSZ), which produced synergistic strain hardening to help with retaining ductility. The strategy of utilizing the shear band delocalization to develop synergistic work hardening for improving the ductility is expected also applicable to other hetero-structured metals consisting of NS and coarse-grained zones. Strain localization by shear bands seems unavoidable in nanostructures. However, in gradient structured materials the detrimental shear bands could be harnessed to benefit ductility.