Chapter Four - Fundamentals of heterostructured materials

Abstract

This chapter introduces heterostructured (HS) materials and the underpinning fundamental science of their superior mechanical properties. Strain partitioning occurs during the deformation of HS materials, which leads to a plastic strain gradient in the hetero-zone boundary-affected region (Hbar). The strain gradient is at least partially accommodated by geometrically necessary dislocations (GNDs), and this produces back stresses in the soft zones and forward stresses in the hard zones. Collectively, the back and forward stresses produce hetero-deformation-induced (HDI) stress and HDI hardening, which can be measured using the loading-unloading-reloading (LUR) procedure during a tensile test. HDI stress before yielding enhances the yield strength, whereas an increase in the HDI stress after yielding produces HDI strain hardening to enhance/retain ductility. Dislocation interactions with the zone boundaries significantly affect the evolution of HDI work hardening. One salient deformation feature of HS materials is the formation of dispersive localized strain bands, which is a stable way to accommodate a large plastic strain without failing the sample. HDI stress can be used to quantitatively describe the Bauschinger effect because both have the same physical origin.