Effect of Stacking-Fault Energy on the Deformed Structures and Work Hardening of Ag and Ni after Scratching during Early Loading Stage

Abstract

Friction wear are accompanied by the formation of refined structures and shear bands in the surface layers of metals and alloys. The propensity for refinement and shear band formation is mainly determined by the stacking-fault energy (SFE). Despite the fact that significant studies have been dedicated to plastic deformation during friction, little effort has been directed toward elucidating the early stages of deformation hardening that is accompanied by the effects of SFE. The research results presented herein focused on the initiation of twin and lamellar shear bands, transformation of nano-grained structures during shear banding, and the deformation hardening of surface layers during the scratching of metals with low and high SFE. Flat samples of low (Ag) and high (Ni) SFE were scratched with a diamond indenter for one to ten friction cycles. The friction surfaces were examined with a field-emission scanning electron microscope. It was shown that the scratch track sizes and amounts of pile-up material were lower for Ag than those for Ni. High deformation hardening of Ag relative to Ni was confirmed by the inhibition of cross-slip and the formation of ultra-fine structures. The deformed structure of Ag after ten scratch cycles was characterized by the formation of core shear bands that were bent in the depth of the deformed layers. It was shown that the balance between deformation hardening and softening was crucial in preserving a steady friction state and forming wear particles.