Chapter 4 - Defect Structure in Low Stacking Fault Energy Nanomaterials

Abstract

In this chapter, the effect of low stacking fault energy (SFE) on a defect structure in nanomaterials is summarized. The low value of SFE leads to a large degree of dislocation dissociation into partials that hinder strongly the cross-slip and climb of dislocations. As a consequence, a relatively large dislocation density develops during severe plastic deformation of low SFE metallic materials. Additionally, the low SFE is accompanied by a small value of twin boundary energy resulting in a significant twinning activity during plastic deformation that alters grain-refinement mechanisms. Among the pure face-centered cubic metals, silver has the lowest SFE. Therefore, the effect of processing conditions and impurity content on dislocation density and twin-fault probability in ultrafine-grained (UFG) and nanocrystalline Ag is revealed and discussed in detail. In addition, the lattice defect structure in UFG alloys with low SFE is also studied. It is shown that the reduction of grain size increases the splitting distance between partials and the probability of occurrence of twinning in UFG and nanocrystalline materials.