Effect of Stacking-Fault Energy on the Deformed Structures and Work Hardening of Ag and Ni after Scratching during Early
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JMEPEG https://doi.org/10.1007/s11665-020-05228-4
Effect of Stacking-Fault Energy on the Deformed Structures and Work Hardening of Ag and Ni after Scratching during Early Loading Stage Alexey Moshkovich and Lev S. Rapoport Submitted: 19 August 2020 / Revised: 8 October 2020 / Accepted: 11 October 2020 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. Keywords
friction, hardening, microstructure, SPD, SFE
1. Introduction Friction and wear are accompanied by strain localization that causes the formation of refined structures and shear bands in the surface layers of metals and alloys, which is similar to those arising from different processes of severe plastic deformation (SPD). As is known, the deformed structures of face-centered cubic (fcc) metals during SPD are determined mainly by the stacking-fault energies (SFE) of metals and alloys. Besides, it was suggested that the twins and stacking faults act as effective sites for blocking slipping and storing dislocations that enhance the mechanical properties of these materials, especially the ductility (Ref 1-5). Moreover, the study of low SFE alloys as, for instance, Cu-30%Zn indicated that stacking faults and twin boundaries play a key role in the grain refinement process (Ref 6-9). The tendencies toward the enhancement of strength and ductility of metals and alloys with low SFE have been thoroughly elucidated (Ref e.g., 8-10). At this case, the nanostructured fcc metals and alloys are isochronally annealed. It is known that the critical stress close to the ultimate strength can lead to necking region and fracture. One of the important aspects
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