The nature of the electroplastic effect in metals

Kopanev, A. A.

doi:10.1007/bf00769953

Cited by 19 publications

(4 citation statements)

References 2 publications

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“…All the equivalent temperatures obtained are near or over the limit of the equilibrium melting temperatures, even though no sign of melt has appeared up to now in the metallographical analyses of the sintered samples. Kopanev (1991) gives us a hint as to the possibility to explain a lower temperature than predicted with EPE.…”

Section: Discussionmentioning

confidence: 94%

Processing characteristics and parameters in capacitor discharge sintering

Fais

2010

Journal of Materials Processing Technology

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Section: Discussionmentioning

confidence: 94%

Processing characteristics and parameters in capacitor discharge sintering

Fais

2010

Journal of Materials Processing Technology

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“…Judging by known data, it may be defined as a specific pulse current effect leading to nonuniform changes in the material at the microlevel because of localized heat release on structural defects [4,5], micrononuniform material properties, deformations [6], and direct interaction of electrons with defects of the crystal lattice [7][8][9][10]. A nonthermal pulse current effect decreases with an increase in current pulse duration or a decrease in microvolume sizes: at a sufficient heating time, temperature in microvolumes equalizes and approaches the average one, which explains only a thermal low-density current effect.…”

Section: Introductionmentioning

confidence: 99%

Simulation of high-density pulse current-induced stress relaxation

Степанов

Babutskii

2007

Strength Mater

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The phenomenological equation relating pulse current-induced relaxation of elastic tensile stresses to current density, initial stresses, and temperature is proposed. The equation allows approximation of experimental data on positive and negative tensile stress relaxation with the above parameters.Keywords: pulse current, positive and negative stress relaxation, phenomenological equation. Introduction.High-density pulse current-based technology is widely used for shaping difficult-to-form metals [1,2]. Its application is determined by several factors. First of all, it is a known thermal current effect in the conducting material involving its uniform heating through energy spent by the current source for charge transfer: collision of charge carriers between themselves and crystal lattice elements results in the transfer of current source work to electrons and the crystal lattice as kinetic energy of chaotic motion or, according to the molecular-kinetic theory, as heat [1]. Moreover, numerous experimental data point to a specific high-density pulse current effect on the metal, which results in a significant decrease in deformation resistance and stress relaxation [2,3]. Such a decrease cannot be explained by an increase in average temperature of the metal since, as a rule, it changes inconsiderably. In the literature this phenomenon was termed the electroplastic effect [2,3].The nature of this effect is as yet little understood. Judging by known data, it may be defined as a specific pulse current effect leading to nonuniform changes in the material at the microlevel because of localized heat release on structural defects [4,5], micrononuniform material properties, deformations [6], and direct interaction of electrons with defects of the crystal lattice [7][8][9][10]. A nonthermal pulse current effect decreases with an increase in current pulse duration or a decrease in microvolume sizes: at a sufficient heating time, temperature in microvolumes equalizes and approaches the average one, which explains only a thermal low-density current effect.Evaluation of a nonthermal pulse current effect should account for the nonuniformity of physicomechanical material properties determining the micrononuniformity of heating and deformation. Pulse current-induced temperature arising in a micrononuniform material may be evaluated in terms of the thermal effect on electrical resistance, heat capacity, and heat conduction of the metal only by numerical methods. The absence of data on material properties necessary for such evaluation is evidence that the development of phenomenological equations for calculating deformation kinetics of the metal with the account of thermal and nonthermal pulse current effects is currently central.Phenomenological equations used in analysis of positive relaxation, when loads decrease under the action of pulse current, and negative relaxation, when loads are growing rather than decreasing after loading, partial unloading, and further pulse current action, are proposed below [11]. Similar behavior of the...

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“…The effect of high-density pulse current on the stress-strain state and mechanical behavior of metals was investigated with a set of physical and phenomenological models, which was detailed in the literature [2][3][4][5][6][7][8][9][10]. However, a knowledge of physical processes determining the change in the stress-strain state of metals on the current passage still remains indeterminate.…”

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confidence: 99%

Evaluation of the high-density pulse current effect on the plastic strain rate in metals

Степанов

Babutskii

2006

Strength Mater

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A direct (nonthermal) high-density pulse current effect on the plastic strain rate in the metal under loading and on the relaxation of elastic stresses in it is evaluated. The evaluation is based on existing notions of electronic conductivity and thermally activated dislocation motion-controlled plastic strain mechanisms in metals. The effect of pulse current on the plastic strain rate is shown to become more and more pronounced with current density, elastic stress levels, and temperature; at low current densities and applied loads its effect is inessential.Keywords: high-density pulse current, plastic strain rate, elastic stress relaxation, thermal activation energy. Notation U -electric potential, V E -electric field intensity, V/m ρ -resistivity, Ω ⋅ m i -current density, A/m 2 n -number of atoms in a unit volume, 1/m 3 n 0 -number of conduction electrons in a unit volume, 1/m 3 b -valency v -mean velocity of electron motion, m/s v -velocity of electron drift, m/s l 0 -mean free electron path, m t 0 -mean time of free electron motion, s t r -time of thermodynamic relaxation, s Q -thermal activation energy, eV/atom Universal physical constants used in calculations [1]: A -Avogadro number, A = ⋅ 6 022 10 23 . mole −1 k -Boltzmann constant, k = ⋅ − 1 380 10 23 . J ( K ) ⋅ −1 m e -rest electron mass, m e = ⋅ − 9 1081 10 31 .Introduction. The effect of high-density pulse current on the stress-strain state and mechanical behavior of metals was investigated with a set of physical and phenomenological models, which was detailed in the literature [2][3][4][5][6][7][8][9][10]. However, a knowledge of physical processes determining the change in the stress-strain state of metals on the current passage still remains indeterminate. The action of pulse current is accompanied by several physical phenomena. At the macrolevel they are -change in plastic strain resistance and plasticity characteristics as a result of a direct (nonthermal) pulse current effect, -nonuniform heating of material areas with current concentrators (cracks and others) as a result of a thermal pulse current effect, -development of nonuniform plastic deformation and formation of residual local stress fields as a result of the pulse current effect and aftereffect.At the microlevel the following phenomena take place: -temperature and stress variations in the vicinity of microdefects as a result of thermal and nonthermal pulse current effects, -microstructure changes, including microcrack healing and grain boundary rearrangement, as a result of intensive thermal activation.The present communication analyzes the mechanism of a direct (nonthermal) high-density pulse current effect on the change in the stress-strain state and on the relaxation of elastic stresses in the metal. Existing notions of electronic conductivity [11,12] and thermally activated dislocation motion-controlled plastic strain [13,14] mechanisms were used to qualitatively evaluate such an effect.Evaluation of the Pulse Current Effect on the Crystal Lattice of the Metal. The basic relationshi...

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The nature of the electroplastic effect in metals

Cited by 19 publications

References 2 publications

Processing characteristics and parameters in capacitor discharge sintering

Processing characteristics and parameters in capacitor discharge sintering

Simulation of high-density pulse current-induced stress relaxation

Evaluation of the high-density pulse current effect on the plastic strain rate in metals

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