Properties of consecutive energy barriers and the associated behavior in plastic flow

Abstract

The properties of consecutive energy-barrier systems are derived from the basic principles of deformation kinetics and from the rate theory as applied to plastic flow. It is shown that these properties are functions of well-defined relations between the activation energy and volumes of the different barriers. In particular, for a system of two consecutive energy barriers, it is shown that the usual equation used to calculate the strain rate ?=ε0/(t1+t2), where t1 and t2 are two waiting times, is only an approximation valid when backward activations are negligible. The behavior of materials, in which plastic flow is controlled by a system of two consecutive energy barriers, was determined rigorously for various experimental conditions. It is shown that the calculated temperature dependence of the flow stress as well as the stress and temperature dependence of the experimental activation volume and strain-rate sensitivity that follow from the properties of consecutive energy barriers are in agreement with experimental observations.