Dynamic strain aging (DSA) in solid solutions is described as diffusion of solute atoms to mobile dislocations, temporarily arrested at obstacles. As a consequence the solute concentration experienced locally by the dislocations depends on the time of arrest and the solute diffusion coefficient. Starting from this idea the dependence of the flow stress on strain rate, temperature, and strain in the presence of DSA is calculated. A criterion for the onset of serrated yielding is formulated. Finally the change in strain rate sensitivity due to DSA is calculated. The theory allows a qualitative and in some respects a quantitative comparison with experimental results of which some examples are given.

Theory of the effect of dynamic strain aging on mechanical properties

This paper attempts an assessment of the current understanding of the phenomenon of “serrated plastic flow”, which manifests itself as serrations, load drops, jerkiness or other discontinuities in the stress-strain curves obtained in constant extension rate tensile tests, and as sudden bursts of strain in constant loading rate tests and in constant load (stress) creep tests (the so called staircase creep). Though one can identify at least seven physical processes that can cause serrations, the discussion here is restricted mainly to serrated yielding in tension tests originating from dynamic strain ageing (dsa). The characteristics of the five types of serrations that have been identified so far and the experimental conditions under which they occur are discussed. The various models of serrated flow that have been put forward are reviewed critically. Some recent results on 316 stainless steel are presented to illustrate the effects of grain size, temperature and strain rate on serrated flow. Manifestations ofdsa other than serrations such as a negative strain rate sensitivity, positive temperature dependence for flow stress and work hardening, and the ductility minimum are also discussed. Finally the various issues to be resolved are enumerated.

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Serrated plastic flow

New observations on the mechanisms of dynamic strain aging and of jerky flow

Mathematics of the portevin-le chatelier effect

The thermo-mechanical properties of low stacking fault energy austenitic Fe18Mn0.6C steel exhibiting twinning-induced plasticity were investigated during uniaxial tensile deformation using infrared thermography. Over a wide strain range, the plastic deformation was by the movement of very few well-defined localized deformation bands. The formation and propagation of Portevin–LeChatelier (PLC) bands lead to type A and type B serrated stress–strain curves, exhibiting a negative strain rate sensitivity. The PLC band properties were analyzed in detail: strain, strain rate and mobile dislocation density within the bands were determined. The microstructures of the un-deformed and deformed Fe18Mn0.6C TWIP steel were studied by transmission electron microscopy. The possible dynamic strain aging processes causing the localized deformation are reviewed.

Localized Deformation due to Portevin-LeChatelier Effect in 18Mn-0.6C TWIP Austenitic Steel

A new type of stress-strain curve and the Portevin-Le Chatelier effect in Au (14 at.% Cu)

The onset of serrated yielding in Au(Cu) alloys

Mobile dislocation density during inhomogenous deformation in Au(14at%Cu)

Determination of the characteristics of portevin-le chatelier bands in Au(14at.%Cu)

Some recent attempts to use the properties of propagating deformation bands in order to obtain information on dislocation parameters are critically discussed.

A. Wijler

Papers

A new type of stress-strain curve and the Portevin-Le Chatelier effect in Au (14 at.% Cu)

The onset of serrated yielding in Au(Cu) alloys

Mobile dislocation density during inhomogenous deformation in Au(14at%Cu)

Determination of the characteristics of portevin-le chatelier bands in Au(14at.%Cu)

Comment on ``Determination of dislocation velocities and densities''