Evidence of enhanced self-organization in the work-hardening stage V of fcc metals

摘要

Stages IV and V of the stress-strain curves of fcc metals, τ = τ(γ), are shown to be clearly discernible in the measurements of Taylor and Quinney on polycrystalline copper strongly deformed at room temperature. The differential stored-energy fraction determined by these workers may serve as an indicator of the degree of self-organization during the deformation process and hence of the dislocation mechanisms involved. In the data there is no indication of a change in mechanism at the stress at which the slope of the work-hardening curve becomes strain independent, conventionally associated with the onset of stage IV. Only at higher stresses is there evidence of enhanced self-organization and hence of a mechanism that differs significantly from stage-III hardening. It is argued that the enhanced self-organization is related to the onset of stage V, characterized by vanishing work-hardening. In this context, a basic difficulty in obtaining quantitative information on stage V from the widely used torsion tests is pointed out.