Plastic Behavior of Metals in Reverse Straining after Large Pre-Strains

Abstract

The present work examines the reversal response of a face-centered cubic (fcc) polycrystalline metal after large pre-strains. While reversal responses among different fcc metals are similar after small pre-strains, they can vary widely after large pre-strains depending on material and microstructure. In this article, these characteristics are considered to be governed by three distinct mechanisms: (1) reverse glide of dislocations previously held by backstresses, (2) reverse glide of dislocations previously held by barriers, and (3) ‘reverse hardening’ by reverse glide over stable dislocation barriers formed in pre-straining. These small-scale mechanisms are incorporated into a polycrystal code to investigate their influence on the macroscopic reversal response and to interpret large strain reversal tests in the literature. It is shown that mechanism (2) is responsible for worksoftening and reductions in hardening rate and mechanism (3) for the overshoot seen in α- brass and other low stacking fault energy alloys. Mechanism (1) is responsible for the Bauschinger effect and occurs in all metals. A large fraction of second phases leads to a strong Bauschinger effect that can either reduce or postpone the effects of mechanisms (2) and (3).