Dense Dispersed Shear Bands in Gradient-Structured Ni

Abstract

During tensile deformation, nanostructured (NS) metals often fail soon after yielding by forming a localized shear band. This chapter reports the observation of high density of shear bands homogeneously dispersed in the NS layer of a gradient Ni sample. The mechanical incompatibility between different layers is believed responsible for the observed mechanical behavior and superior properties. Shear banding is shear strain localization in a narrow zone, which often runs across multiple grain boundaries and twin boundaries during plastic deformation of polycrystalline metals. It is caused by local strain instability and accompanied with dramatic local orientation and texture change. Strain hardening was believed necessary to prevent shear banding. Nanostructured materials are especially prone to shear banding due to their low strain hardening capability. In the gradient structured metals, shear bands may be initiated in the NS layers. NS layers and microstructure gradients were produced with different processing techniques and parameters to study the mechanism of shear band nucleation and growth.