Theory of the effect of dynamic strain aging on mechanical properties
TL;DR: In this paper, the authors described dynamic strain aging (DSA) in solid solutions as diffusion of solute atoms to mobile dislocations, temporarily arrested at obstacles, and calculated the dependence of the flow stress on strain rate, temperature, and strain in the presence of DSA.
Abstract: 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.
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TL;DR: In this paper, the authors present a review of recent developments in the field of deformation behavior of high manganese face-centered cubic γ-Fe alloys, referred to as twinning-induced plasticity, or TWIP, steels.
884 citations
TL;DR: In this paper, the authors present 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).
Abstract: 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.
534 citations
TL;DR: In this article, the rate sensitivity of the flow stress was investigated as a function of pre-strain for a commercial nickel alloy (INCONEL 600) and for polycrystalline Al-1% Mg. over a wide temperature range encompassing the regime of jerky flow.
517 citations
TL;DR: In this paper, a model for the critical strains associated with the Portevin-Le Châtelier effect (PLC) in terms of the strain dependence of the densities of mobile and forest dislocations is proposed.
Abstract: A model is proposed for the critical strains associated with the Portevin-Le Châtelier effect (PLC) in terms of the strain dependence of the densities of mobile and forest dislocations. The classical critical condition for the onset of the PLC effect, viz. that of vanishing of the strain rate sensitivity of flow stress under the influence of dynamic strain aging is reexamined. The analysis takes into account the strain dependence of a key quantity: the elementary strain produced when all mobile dislocations perform a successful thermally activated step through the forest obstacles. This elementary strain is estimated by studying a system of coupled differential equations for the evolution of the two densities. Results are obtained in semi-quantitative form and compared with available data. It is shown that the following effects are consistently explained: the occurrence of critical strains for the onset and termination of jerky flow, occasional observation of two PLC regimes within the same deformation curve, the behaviour of the critical strains at high strain rates and low temperatures and, possibly, the particular behaviour exhibited by some alloys at low strain rates and high temperatures. Consequences for the “friction” and “forest” models of dynamic strain aging are discussed.
466 citations
TL;DR: In this paper, the localisation of plastic flow due to dynamic strain ageing is evaluated taking into account transient behaviour associated with the time dependence of the solute composition at mobile dislocations.
332 citations
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TL;DR: In this article, the authors derived a model for the onset of the Portevin-Le Chatelier effect in substitutional alloys, based on the solute locking of dislocations temporarily arrested at obstacles in the glide path.
570 citations
TL;DR: In this article, it is shown mathematically that the strain rate at any point in the tensile material must make jumps as a function of time, whenever the stress as the function of strain rate, for given strain, goes through a maximum and minimum.
294 citations
43 citations
TL;DR: In this article, the onset of serrated yielding in Au(Cu) alloys has been investigated as a function of strain rate, temperature, Cu concentration and initial state of order both in prequenched and furnace cooled specimens.
34 citations