an investigation on dislocation density in cold-rolled copper...

Hindawi Publishing CorporationISRN CorrosionVolume 2013 Article ID 921825 6 pageshttpdxdoiorg1011552013921825

Research ArticleAn Investigation on Dislocation Density in Cold-RolledCopper Using Electrochemical Impedance Spectroscopy

Elyas Rafiee1 Mansour Farzam1 Mohammad Ali Golozar2 and Ali Ashrafi3

1 Technical Inspection Engineering Department Petroleum University of Technology Abadan Iran2Department of Materials Engineering Isfahan University of Technology Isfahan 8415683111 Iran3Department of Materials Science and Engineering Shahid Chamran University of Ahvaz Iran

Correspondence should be addressed to Mansour Farzam farzamputacir

Received 7 February 2013 Accepted 1 March 2013

Academic Editors C-H Hsu and S J Lee

Copyright copy 2013 Elyas Rafiee et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Variation of electrochemical impedance with dislocation density was investigated using electrochemical impedance spectroscopy(EIS) For this purpose EIS measurements were carried out on 10 20 30 40 and 50 cold-rolled commercially pure copper in01M NaCl (pH = 2) solution Nyquist plots illustrated that the electrochemical reactions are controlled by both charge transferand diffusion process Increasing dislocation density the magnitude of electrochemical impedance of samples was decreasedDecreasing magnitude of impedance at intermediate frequencies indicated increasing double-layer capacitance Charge transferresistance decreased from value 3296Ωcm2 for annealed sample to 1863Ωcm2 for sample with maximum dislocation density(172 times 1015mminus2) Phase angles were lower for samples that contained more dislocation density indicating more tendencies to lossof electrons and releasing atoms into electrolyte

1 Introduction

It has been reported that after deformation of a metalmore than yield limit hardening occurs which is due tomultiplication and rearrangement of dislocations and themore severe the cold deformation the more generation ofdislocations [1ndash4]

Tensile properties of metals such as yield strength ulti-mate tensile strength and ductility depend heavily on densityof dislocations Also dislocation density plays a significantrole on brittle to ductile transition fatigue hardness workhardening and plastic behavior of metals and alloys [5ndash8] Furthermore dislocations have considerable effect onphysical properties of metals such as density [9ndash12] thermalconductivity [13 14] and electrical resistivity [9 13 14]

In this respect some researchers [5 15 16] have investi-gated density of dislocations by ultrasound waves and haveproposed some relationships between dislocation density andchanges in the speed of elastic waves propagation Sablikand Landgraf [17 18] Kobayashi et al [19] and Yaegashi[20] reported some relationships between dislocation density

and magnetic properties Kikuchi et al [21] investigated therelation between AC permeability and dislocation density inpure iron as well Also other researchers tried to correlatedislocation density with stored energy and critical transfor-mation temperatures using differential scanning calorimetry[4 7 22] and high-resolution dilatometry [23] respectively

The strain field and energy of dislocation line intersectswith metal surface increase the susceptibility of the metalto corrosion [24ndash26] Since corrosion is an electrochemicaldegradation electrochemical techniques can be utilized forstudying the corrosion process Electrochemical impedancespectroscopy (EIS) is one of the most useful nondestructivesensitive powerful and fastest electrochemical characteriza-tion techniques presently available [27ndash29] and is becominga beloved analytical instrument in evaluation of electricalproperties and interfaces of a wide range of materialsThis technique includes a comparatively simple electricalmeasurements that can easily be automated and its resultsbecome correlated with many complex materials variables[30ndash32] Therefore it seems that it can be used for studyingthe variation of dislocations density in a metal Having this

2 ISRN Corrosion

in mind the aim of this work is to investigate the effect ofdislocation density on electrochemical impedance in cold-rolled copper using EIS

2 Experimental

In order to prepare samples with different dislocation densi-ties to perform electrochemicalmeasurements commerciallypure (9998) copper strips were annealed at 500∘C for2 h to remove residual stresses and obtain a recrystallizedmicrostructure having the lowest dislocation density fol-lowed by cold rolling at ambient temperature to obtain 10 2030 40 and 50 reductions in area

Tensile tests were carried out on cold-rolled strips todetermine the yield stresses of samples In this regardstandard tensile specimens were cut from strips according toASTM E8-04 with gauge length of 50mm Tensile tests wereperformed using a constant strain rate of 2 times 10minus3 sminus1

Samples for electrochemical tests were cut from cross-section of rolled strips In order to avoid further deformationduring cutting samples were cut using electrodischargemachining (EDM) method Samples and connecting copperwire were coated by Epoxy resin as to expose only one side ofsamples to solution All samples were mechanically polishedwith silicon carbide abrasive paper down to 2000 gradeand then 005120583m Al

2O3slurry was used to get mirror-like

finished surfaces Finally samples were ultrasonically washedin ethanol This treatment ensures good reproducibility ofelectrochemical measurements These specimens were usedas working electrode in the EIS tests The EIS measurementswere done using potentiostatgalvanostat autolab

To achieve the steady state open-circuit potential speci-mens were immersed in the solution for 20min Impedancemeasurements were made at open-circuit potential using asinusoidal signal of 10mV amplitude and frequencies in therange of 001Hz to 100 kHz in a conventional three-electrodeglass cell containing an AgAgCl reference electrode and Ptcounter electrode All tests were performed in 01M NaClsolution at room temperature and pH value of 2 At least threeEIS tests were carried out for each sample

3 Results and Discussion

Figure 1 shows stress-strain curves of cold-rolled speci-mens Dislocation multiplication and their interactions leadto increasing ultimate tensile strength yield strength anddecreasing ductility as plastic deformation increases

Yield strength and true strain values of cold-rolled sam-ples are listed in Table 1 As it can be seen yield strength hasincreased by cold working

Empirical data achieved by numerous metals and alloyssuggests that the yield stress of a metal is related to the totaldislocation density by

120590 = 1205900+119872120572119866119887120588

12 (1)

where 120572 is a constant119872 average Taylor factor 1205900is friction

stress that for FCC metals is equal to zero 119866 is the shearmodulus 119887 is the length of Burgers vector and 120588 is the

Table 1 Yield strength and true strain corresponding to eachamount of cold work

Specimen code C10 C9 C8 C7 C6 C5Cold work () 0 10 20 30 40 50True strain 0 009 018 026 034 040Yield strength(02) (MPa) 16254 22188 25515 27533 29052 29231

Engi

neer

ing

stres

s (M

Pa)

350

300

250

200

150

100

50

00 5 10 15 20 25 30 35 40 45 50

Engineering strain ()

C5C6C7

C8C9C10

Figure 1 Stress-strain curves of cold rolled samples

measured dislocation density [7 12 33ndash35] This relationhas some theoretical bases and has been proved in manyexperimental works performed on metals and alloys [33]

Employing yield stress values obtained from stress-straincurves and theTaylor factor119872 = 306120590

0= 0 for FCCmetals

120572 = 02 119866 = 46GPa and 119887 = 25 times 10minus10m for copper[36] dislocation densities corresponding to each deformationin this work were calculated (Table 2) Results were in agood agreement with former works by other researchersfor example [37] As it can be seen by increasing deforma-tion dislocation density is increased from 533 times 1014mminus2for annealed specimen to 172 times 1015mminus2 for maximumdeformed specimen (true strain = 04)

Cold working is capable of affecting not only themechan-ical properties of metals but also their corrosion behaviorHowever there is not a clarified correlation between coldworking and corrosion properties because the cold workinginfluences differently the corrosion resistance depending onmetal deformation and environment [38]

Figure 2 shows Nyquist plots of deformed samples after20min immersion in 01M sodium chloride solution (pH =2) at 25∘C These impedance diagrams indicate a depressedcapacitive semicircle and diffusion line for all samplesDepressed capacitive semicircles describe the charge transferreaction occurring during copper dissolution at corrosionpotential In electrochemical systems the depressed semicir-cles in Nyquist diagram have been ascribed to the roughnessof surface the existence of a porous corrosion product filmor the inhomogeneous nature of the surface [31 32 39 40]

ISRN Corrosion 3

Table 2 Dislocation densities corresponding to each deformation in this work

Specimen code C10 C9 C8 C7 C6 C5Dislocation density (mminus2) 533 times 1014 994 times 1014 131 times 1015 151 times 1015 17 times 1015 172 times 1015

300

250

200

150

100

50

00 100 200 300 400 500

C5C6C7

C8C9C10

minus119885998400998400

(Ωcm

2)

119885998400 (Ω cm2)

Figure 2 Nyquist plots of deformed samples

Diameter of the semicircles indicates charge transferresistance It can be seen that the diameter of the semicir-cles varies with the dislocation density of the samples anddecreases by increasing dislocation density

Corrosion of copper in NaCl solutions having low chlo-ride concentrations occurs through the formation of CuClwhich is not protective and is converted toCuCl

2

minus by reactingwith chloride ions In this condition CuCl

2

minus is created at themetal surface and then diffuses into the bulk solution [41ndash43]Reactions are as follows

Cu 997888rarr Cu+ + eminus (2)

Cu+ + Clminus 997888rarr CuClads (3)

CuClads + Clminus997888rarr CuCl

2

minus (4)

The cathodic reactions in this environment are oxygenand H+ reduction according to

O2+ 4H+ + 4119890minus 997888rarr 2H

2O (5)

2H+ + 2119890minus 997888rarr H2

(6)

Here the semicircles are followed by a diffusion line atlower frequencies attributed to the diffusion of species toor from metal surface and illustrate that the electrochemicalreactions are controlled by both charge transfer and diffusionprocess According to the previous equations corrosion ofcopper will depend on the movement of O

2 H+ CuCl

2

minusand Cu+ to and from metalsolution interface On the baseof mixed potential theory enhanced movement of Clminus orCuCl2

minus to or from the electrode surface will increase theanodic reaction rate while enhancement of O

2and H+

movementwill accelerate the cathodic reaction rate thereforecorrosion rate will increase However it has been reported

minus2 minus1 0 1 2 3 4 5

600

500

400

300

200

100

0

C5C6C7

C8C9C10

∣119885∣

(Ωcm

2)

log(119891) (Hz)

Figure 3 Bode diagram of samples

that mostly transport of CuCl2

minus from metal surface to thebulk solution controls the corrosion rate [41 44ndash46]

Bode diagrams of samples are plotted in Figure 3Although the differences created are small increasing dislo-cation density the impedance magnitude of samples surfaceis decreased The Bode plots show resistive region at highfrequencies and capacitive region at intermediate frequenciesbut do not show a clear resistive region (horizontal line)at low frequencies This strict descending behavior at lowfrequencies is due to Warburg impedance

As mentioned previous the magnitude of impedance inbode plot at intermediate frequencies is related to capacitivebehavior of electrochemical system and as seen this valuedecreases by increasing deformation Since this value ofimpedance is proportional to reciprocal of capacitance (119885 prop1119862) therefore double-layer capacitance will increase byincreasing dislocation density The double-layer capacitanceis calculated by

119862 = 1205760120576119860

119889 (7)

where 1205760is the vacuum permittivity 120576 is the dielectric

constant of the medium 119860 is area of the electrode surfaceand 119889 is thickness of double layersThus since for all samples1205760and 120576 are constant and impact of surface areas was applied

increase of capacitance is due to the decrease of double-layerthickness

Bode-phase plots of samples shown in Figure 4 are usedfor investigating the variations of phase angle and timeconstants with plastic deformation All of these diagramsshow two time constants one at low frequencies that belongsto CuCl film and the other at higher frequencies referringto double layers No changes in general shape of curveswith increasing dislocation density show identical reactionmechanisms for all samples

4 ISRN Corrosion

C5C6C7

C8C9C10

4540353025201510

50minus2 minus1 0 1 2 3 4 5 6

Phas

e ang

le (d

eg)

log(119891) (Hz)

Figure 4 Bode-phase plots of samples

119877119904 119876

119882119877ct

Figure 5 Used equivalent circuit for fitting experimental data

As it is seen in bode-phase plots generally the moredislocation density the lower phase angle Increasing surfaceenergy of metal induced by dislocations the tendency to lossof electrons and releasing atoms into electrolyte acceleratesTherefore after polarizing by a signal in EIS test it is expectedthat current response in sample with higher dislocationdensity be faster hence phase angle at a constant frequencybe lower

A significant trouble for impedance spectroscopy athigh frequencies is the parasitic segments and the phaseangles linked to the potentiostatic control of the system [31]therefore this behavior of some points at high frequencies isattributed to this fact

Using equivalent circuit shown in Figure 5 the valuesof equivalent circuit parameters calculated by fitting ofimpedance spectra of samples are listed in Table 3 Inthis equivalent electrical circuit (EEC) 119877

119904is the solution

resistance 119876 represents the capacitance of the double layers119877ct the charge transfer resistance and 119882 is the Warburgimpedance

Use of Constant Phase Element (CPE) instead of purecapacitance (119876 in the EEC) is due to making a good fittingConstant phase element indicates the nonideal capacitivebehavior of the electrochemical system because on themicro-scopic view electrode surface is rough and inhomogeneous[30]

As exhibited in Table 3 the charge transfer resistance 119877ctdecreases while the Warburg impedance 119882 increases withincreasing cold work Thus it can be concluded that thecorrosion rate and themovement of ions within the corrosionproduct increase with increasing deformation Decrease ofcharge transfer resistance with straining is chiefly ascribedto a higher migration of atoms from active sites in thisenvironment

Table 3Values of equivalent circuit parameters calculated by fitting

Sample 119877119904

(Ωcm2)

CPE119877ct

(Ωcm2)119882

(s12Ωcm2)1198840

(s119899Ωcm2) 119899

C10 1898 0002002 08 3296 001104C9 1709 0002221 08 2961 001227C8 1654 0001491 08 260 001459C7 1549 0001598 08 2437 001577C6 164 0001579 08 2235 001505C5 1367 0001895 08 1863 001806

CalculatedMeasured

0 50 100 150 200 250 300 350 400 450 500

300

250

200

150

100

50

0minus119885119894

(Ωcm

2)

119885119903 (Ω cm2)

Figure 6 Good agreement between the experimental and simulateddata generated using the circuit

Since dislocations enhance atomic migration plasticdeformation may promote and accelerate formation ofsurface CuCl film As regards charge transfer resistance 119877ctcontinuously decreasing with increasing deformation it canbe concluded that CuCl film formed on electrode surfacedoes not have enough adhesion and compactness to protectthe metal and is not able to prevent further dissolution ofsurface atoms of metal what has been reported by otherresearchers [41ndash43]

In Figure 6 white squares represent the measured dataand solid line represents the best fit using the equivalentcircuit shown in Figure 5 It can be seen that there is a verygood agreement between the experimental and simulateddata generated using the EEC indicating the validity ofproposed EEC

4 Conclusions

(1) Electrochemical impedance spectroscopy at corro-sion potential is very sensitive to variation of electro-chemical activity induced by dislocations

(2) Semicircles in Nyquist plots are followed by a dif-fusion line at lower frequencies that illustrates thatthe electrochemical reactions are controlled by bothcharge transfer and diffusion process

(3) Charge transfer resistance of samples decreases withincreasing dislocation density

ISRN Corrosion 5

(4) Decreasing the magnitude of impedance at interme-diate frequencies by increasing dislocation densityindicates decrease of the double-layer thickness

(5) Bode-phase diagrams show two time constants andidentical reaction mechanism for all samples

(6) Increasing dislocation density leads to decreasingphase angle indicating more tendencies to loss ofelectrons and releasing atoms into electrolyte

Acknowledgments

This work has been done under the financial support of theNational Iranian Drilling Company (NIDC) The authors aregrateful to Engineer Darbandi and RampD center of NIDC

References

[1] S CWang Z Zhu andM J Starink ldquoEstimation of dislocationdensities in cold rolled Al-Mg-Cu-Mn alloys by combinationof yield strength data EBSD and strength modelsrdquo Journal ofMicroscopy vol 217 no 2 pp 174ndash178 2005

[2] A Ciuplys J Vilys V Ciuplys andVKvedaras ldquoInvestigation ofdislocation structure of low carbon steel during static loadingrdquoMechanika vol 4 pp 59ndash66 2006

[3] H D Chandler ldquoWork hardening characteristics of copperfromconstant strain rate and stress relaxation testingrdquoMaterialsScience and Engineering A vol 506 no 1-2 pp 130ndash134 2009

[4] MKazeminezhad ldquoRelationship between the stored energy andindentation hardness of copper after compression test modelsand measurementsrdquo Journal of Materials Science vol 43 no 10pp 3500ndash3504 2008

[5] A Maurel V Pagneux F Barra and F Lund ldquoUltrasound as aprobe of plasticity The interaction of elastic waves with dislo-cationsrdquo International Journal of Bifurcation and Chaos vol 19no 8 pp 2765ndash2781 2009

[6] Y BWang J C Ho Y Cao et al ldquoDislocation density evolutionduring high pressure torsion of a nanocrystalline Ni-Fe alloyrdquoApplied Physics Letters vol 94 Article ID 091911 3 pages 2009

[7] M Verdier I Groma L Flandin J Lendvai Y Brechet andP Guyot ldquoDislocation densities and stored energy after coldrolling of Al-Mg alloys investigations by resistivity and differ-ential scanning calorimetryrdquo Scripta Materialia vol 37 no 4pp 449ndash454 1997

[8] S Graca R Colaco P A Carvalho and R Vilar ldquoDetermi-nation of dislocation density from hardness measurements inmetalsrdquoMaterials Letters vol 62 pp 3812ndash3814 2008

[9] G E Dieter and D Bacon Mechanical Metallurgy McGraw-Hill Singapore 1988

[10] F Garofalo and H A Wriedt ldquoDensity change in an austeniticstainless steel deformed in tension or compressionrdquo ActaMetallurgica vol 10 no 11 pp 1007ndash1012 1962

[11] R E Smallman and R J Bishop Modern Physical Metallurgyand Materials Engineering Elsevier Science 1999

[12] R E Smallman and A H W Ngan Physical Metallurgy andAdvanced Materials Elsevier Burlington Vt USA 2007

[13] D B Sirdeshmukh L Sirdeshmukh andK G SubhadraAtom-istic Properties of Solids Springer New York NY USA 2011

[14] F Khodabakhshi and M Kazeminezhad ldquoThe effect of con-strained groove pressing on grain size dislocation density and

electrical resistivity of low carbon steelrdquo Materials and Designvol 32 no 6 pp 3280ndash3286 2011

[15] N Mujica M A T Cerda R Espinoza J Lisoni and F LundldquoUltrasound as a probe of dislocation density in aluminumrdquoActa Materialia vol 60 pp 5828ndash5837 2012

[16] F Barra A Caru M T Cerda et al ldquoMeasuring dislocationdensity in aluminum with resonant ultrasound spectroscopyrdquoInternational Journal of Bifurcation and Chaos vol 19 no 10pp 3561ndash3565 2009

[17] M J Sablik ldquoModeling the effect of grain size and dislocationdensity on hysteretic magnetic properties in steelsrdquo Journal ofApplied Physics vol 89 no 10 pp 5610ndash5613 2001

[18] M J Sablik and F J G Landgraf ldquoModeling microstructuraleffects onhysteresis loopswith the samemaximumfluxdensityrdquoIEEE Transactions on Magnetics vol 39 no 5 pp 2528ndash25302003

[19] S Kobayashi T Kimura S Takahashi Y Kamada and HKikuchi ldquoQuantitative evaluation of dislocation density usingminor-loop scaling relationsrdquo Journal of Magnetism and Mag-netic Materials vol 320 no 20 pp e551ndashe555 2008

[20] K Yaegashi ldquoDependence of magnetic susceptibility on dis-location density in tensile deformed iron and Mn-steelrdquo ISIJInternational vol 47 no 2 pp 327ndash332 2007

[21] H Kikuchi Y Henmi T Liu et al ldquoThe relation between ACpermeability and dislocation density and grain size in pureironrdquo International Journal of Applied Electromagnetics andMechanics vol 25 no 1ndash4 pp 341ndash346 2007

[22] A Karimi Taheri Kazeminezhad and A Kiet Tieu ldquotheoret-ical and experimental evaluation of dislocation density in aworkpiece after formingrdquo Iranian Journal of Materials Scienceamp Engineering vol 4 pp 1ndash8 2007

[23] C Garcia-Mateo F G Caballero C Capdevila and C GD Andres ldquoEstimation of dislocation density in bainiticmicrostructures using high-resolution dilatometryrdquo ScriptaMaterialia vol 61 no 9 pp 855ndash858 2009

[24] H Miyamoto K Harada T Mimaki A Vinogradov and SHashimoto ldquoCorrosion of ultra-fine grained copper fabricatedby equal-channel angular pressingrdquo Corrosion Science vol 50no 5 pp 1215ndash1220 2008

[25] W Li and D Y Li ldquoVariations of work function and corrosionbehaviors of deformed copper surfacesrdquo Applied Surface Sci-ence vol 240 no 1ndash4 pp 388ndash395 2005

[26] S Yin and D Y Li ldquoEffects of prior cold work on corrosionand corrosive wear of copper in HNO

3and NaCl solutionsrdquo

Materials Science and Engineering A vol 394 no 1-2 pp 266ndash276 2005

[27] R G Kelly J R Scully D W Shoesmith and R G BuchheitElectrochemical Techniques in Corrosion Science and Engineer-ing Marcel Dekker 2002

[28] A S Hamdy E El-Shenawy and T El-Bitar ldquoElectrochemicalimpedance spectroscopy study of the corrosion behavior ofsome niobium bearing stainless steels in 35 NaClrdquo Inter-national Journal of Electrochemical Science vol 1 pp 171ndash1802006

[29] N D Cogger An Introduction to Electrochemical ImpedanceMeasurement Solartron Analytical 1999

[30] E Barsoukov and J R Macdonald Impedance SpectroscopyTheory Experiment and Applications JohnWiley amp Sons 2005

[31] F Scholz Electroanalytical Methods Guide to Experiments andApplications Springer 2010

6 ISRN Corrosion

[32] X Z Yuan C Song H Wang and J Zhang ElectrochemicalImpedance Spectroscopy in PEM Fuel Cells Fundamentals andApplications Springer 2009

[33] F Barlat M V Glazov J C Brem and D J Lege ldquoA simplemodel for dislocation behavior strain and strain rate hardeningevolution in deforming aluminum alloysrdquo International Journalof Plasticity vol 18 no 7 pp 919ndash939 2002

[34] R Abbaschian R E Reed-Hill and L Abbaschian Physi-cal Metallurgy Principles Cengage Learning Stamford ConnUSA 2009

[35] E Hosseini and M Kazeminezhad ldquoDislocation structure andstrength evolution of heavily deformed tantalumrdquo InternationalJournal of Refractory Metals and Hard Materials vol 27 no 3pp 605ndash610 2009

[36] W D CallisterMaterials Science and Engineering An Introduc-tion John Wiley amp Sons New York NY USA 2007

[37] E Schafler M Zehetbauer and T Ungar ldquoMeasurement ofscrew and edge dislocation density by means of X-ray Braggprofile analysisrdquoMaterials Science and Engineering A vol 319ndash321 pp 220ndash223 2001

[38] A Robin G A S Martinez and P A Suzuki ldquoEffect of cold-working process on corrosion behavior of copperrdquoMaterials ampDesign vol 34 pp 319ndash324 2012

[39] C Fonseca and M A Barbosa ldquoCorrosion behaviour of tita-nium in biofluids containing H

2O2studied by electrochemical

impedance spectroscopyrdquo Corrosion Science vol 43 no 3 pp547ndash559 2001

[40] C L Zeng W Wang and W T Wu ldquoElectrochemical impeda-ncemodels formolten salt corrosionrdquoCorrosion Science vol 43no 4 pp 787ndash801 2001

[41] EM Sherif and S-M Park ldquo2-Amino-5-ethyl-134-thiadiazoleas a corrosion inhibitor for copper in 30 NaCl solutionsrdquoCorrosion Science vol 48 pp 4065ndash4079 2006

[42] L Hu S Zhang W Li and B Hou ldquoElectrochemical and ther-modynamic investigation of diniconazole and triadimefon ascorrosion inhibitors for copper in synthetic seawaterrdquoCorrosionScience vol 52 no 9 pp 2891ndash2896 2010

[43] E S M Sherif ldquoEffects of 2-amino-5-(ethylthio)-134-thiadi-azole on copper corrosion as a corrosion inhibitor in 3 NaClsolutionsrdquo Applied Surface Science vol 252 no 24 pp 8615ndash8623 2006

[44] M Cubillos M Sancy J Pavez et al ldquoInfluence of 8-aminoqui-noline on the corrosion behaviour of copper in 01 M NaClrdquoElectrochimica Acta vol 55 pp 2782ndash2792 2010

[45] S M Milic and M M Antonijevic ldquoSome aspects of coppercorrosion in presence of benzotriazole and chloride ionsrdquoCorrosion Science vol 51 pp 28ndash34 2009

[46] E M Sherif R M Erasmus and J D Comins ldquoCorrosion ofcopper in aerated synthetic seawater solutions and its inhibitionby 3-amino-124-triazolerdquo Journal of Colloid and InterfaceScience vol 309 no 2 pp 470ndash477 2007

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CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014


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MetallurgyJournal of


BioMed Research International


Volume 2014

MaterialsJournal of

Nano

materials


Journal ofNanomaterials

2 ISRN Corrosion

in mind the aim of this work is to investigate the effect ofdislocation density on electrochemical impedance in cold-rolled copper using EIS

2 Experimental

In order to prepare samples with different dislocation densi-ties to perform electrochemicalmeasurements commerciallypure (9998) copper strips were annealed at 500∘C for2 h to remove residual stresses and obtain a recrystallizedmicrostructure having the lowest dislocation density fol-lowed by cold rolling at ambient temperature to obtain 10 2030 40 and 50 reductions in area

Tensile tests were carried out on cold-rolled strips todetermine the yield stresses of samples In this regardstandard tensile specimens were cut from strips according toASTM E8-04 with gauge length of 50mm Tensile tests wereperformed using a constant strain rate of 2 times 10minus3 sminus1

Samples for electrochemical tests were cut from cross-section of rolled strips In order to avoid further deformationduring cutting samples were cut using electrodischargemachining (EDM) method Samples and connecting copperwire were coated by Epoxy resin as to expose only one side ofsamples to solution All samples were mechanically polishedwith silicon carbide abrasive paper down to 2000 gradeand then 005120583m Al

2O3slurry was used to get mirror-like

finished surfaces Finally samples were ultrasonically washedin ethanol This treatment ensures good reproducibility ofelectrochemical measurements These specimens were usedas working electrode in the EIS tests The EIS measurementswere done using potentiostatgalvanostat autolab

To achieve the steady state open-circuit potential speci-mens were immersed in the solution for 20min Impedancemeasurements were made at open-circuit potential using asinusoidal signal of 10mV amplitude and frequencies in therange of 001Hz to 100 kHz in a conventional three-electrodeglass cell containing an AgAgCl reference electrode and Ptcounter electrode All tests were performed in 01M NaClsolution at room temperature and pH value of 2 At least threeEIS tests were carried out for each sample

3 Results and Discussion

Figure 1 shows stress-strain curves of cold-rolled speci-mens Dislocation multiplication and their interactions leadto increasing ultimate tensile strength yield strength anddecreasing ductility as plastic deformation increases

Yield strength and true strain values of cold-rolled sam-ples are listed in Table 1 As it can be seen yield strength hasincreased by cold working

Empirical data achieved by numerous metals and alloyssuggests that the yield stress of a metal is related to the totaldislocation density by

120590 = 1205900+119872120572119866119887120588

12 (1)

where 120572 is a constant119872 average Taylor factor 1205900is friction

stress that for FCC metals is equal to zero 119866 is the shearmodulus 119887 is the length of Burgers vector and 120588 is the

Table 1 Yield strength and true strain corresponding to eachamount of cold work

Specimen code C10 C9 C8 C7 C6 C5Cold work () 0 10 20 30 40 50True strain 0 009 018 026 034 040Yield strength(02) (MPa) 16254 22188 25515 27533 29052 29231

Engi

neer

ing

stres

s (M

Pa)

350

300

250

200

150

100

50

00 5 10 15 20 25 30 35 40 45 50

Engineering strain ()

C5C6C7

C8C9C10

Figure 1 Stress-strain curves of cold rolled samples

measured dislocation density [7 12 33ndash35] This relationhas some theoretical bases and has been proved in manyexperimental works performed on metals and alloys [33]

Employing yield stress values obtained from stress-straincurves and theTaylor factor119872 = 306120590

0= 0 for FCCmetals

120572 = 02 119866 = 46GPa and 119887 = 25 times 10minus10m for copper[36] dislocation densities corresponding to each deformationin this work were calculated (Table 2) Results were in agood agreement with former works by other researchersfor example [37] As it can be seen by increasing deforma-tion dislocation density is increased from 533 times 1014mminus2for annealed specimen to 172 times 1015mminus2 for maximumdeformed specimen (true strain = 04)

Cold working is capable of affecting not only themechan-ical properties of metals but also their corrosion behaviorHowever there is not a clarified correlation between coldworking and corrosion properties because the cold workinginfluences differently the corrosion resistance depending onmetal deformation and environment [38]

Figure 2 shows Nyquist plots of deformed samples after20min immersion in 01M sodium chloride solution (pH =2) at 25∘C These impedance diagrams indicate a depressedcapacitive semicircle and diffusion line for all samplesDepressed capacitive semicircles describe the charge transferreaction occurring during copper dissolution at corrosionpotential In electrochemical systems the depressed semicir-cles in Nyquist diagram have been ascribed to the roughnessof surface the existence of a porous corrosion product filmor the inhomogeneous nature of the surface [31 32 39 40]

ISRN Corrosion 3



300

250

200

150

100

50

00 100 200 300 400 500

C5C6C7

C8C9C10

minus119885998400998400

(Ωcm

2)

119885998400 (Ω cm2)




2


2





2

minus (4)


O2+ 4H+ + 4119890minus 997888rarr 2H

2O (5)

2H+ + 2119890minus 997888rarr H2

(6)


2 H+ CuCl

2



2and H+



600

500

400

300

200

100

0

C5C6C7

C8C9C10

∣119885∣

(Ωcm

2)

log(119891) (Hz)






119862 = 1205760120576119860

119889 (7)





4 ISRN Corrosion

C5C6C7

C8C9C10

4540353025201510

50minus2 minus1 0 1 2 3 4 5 6

Phas

e ang

le (d

eg)

log(119891) (Hz)


119877119904 119876

119882119877ct










Sample 119877119904

(Ωcm2)

CPE119877ct

(Ωcm2)119882

(s12Ωcm2)1198840

(s119899Ωcm2) 119899

C10 1898 0002002 08 3296 001104C9 1709 0002221 08 2961 001227C8 1654 0001491 08 260 001459C7 1549 0001598 08 2437 001577C6 164 0001579 08 2235 001505C5 1367 0001895 08 1863 001806

CalculatedMeasured

0 50 100 150 200 250 300 350 400 450 500

300

250

200

150

100

50

0minus119885119894

(Ωcm

2)

119885119903 (Ω cm2)




4 Conclusions




ISRN Corrosion 5




Acknowledgments


References



































6 ISRN Corrosion

























CeramicsJournal of







Biomaterials




Journal of


Journal of


Volume 2014




CoatingsJournal of

Advances in









Volume 2014

MaterialsJournal of

Nano

materials



ISRN Corrosion 3



300

250

200

150

100

50

00 100 200 300 400 500

C5C6C7

C8C9C10

minus119885998400998400

(Ωcm

2)

119885998400 (Ω cm2)




2


2





2

minus (4)


O2+ 4H+ + 4119890minus 997888rarr 2H

2O (5)

2H+ + 2119890minus 997888rarr H2

(6)


2 H+ CuCl

2



2and H+



600

500

400

300

200

100

0

C5C6C7

C8C9C10

∣119885∣

(Ωcm

2)

log(119891) (Hz)






119862 = 1205760120576119860

119889 (7)





4 ISRN Corrosion

C5C6C7

C8C9C10

4540353025201510

50minus2 minus1 0 1 2 3 4 5 6

Phas

e ang

le (d

eg)

log(119891) (Hz)


119877119904 119876

119882119877ct










Sample 119877119904

(Ωcm2)

CPE119877ct

(Ωcm2)119882

(s12Ωcm2)1198840

(s119899Ωcm2) 119899

C10 1898 0002002 08 3296 001104C9 1709 0002221 08 2961 001227C8 1654 0001491 08 260 001459C7 1549 0001598 08 2437 001577C6 164 0001579 08 2235 001505C5 1367 0001895 08 1863 001806

CalculatedMeasured

0 50 100 150 200 250 300 350 400 450 500

300

250

200

150

100

50

0minus119885119894

(Ωcm

2)

119885119903 (Ω cm2)




4 Conclusions




ISRN Corrosion 5




Acknowledgments


References



































6 ISRN Corrosion

























CeramicsJournal of







Biomaterials




Journal of


Journal of


Volume 2014




CoatingsJournal of

Advances in









Volume 2014

MaterialsJournal of

Nano

materials



4 ISRN Corrosion

C5C6C7

C8C9C10

4540353025201510

50minus2 minus1 0 1 2 3 4 5 6

Phas

e ang

le (d

eg)

log(119891) (Hz)


119877119904 119876

119882119877ct










Sample 119877119904

(Ωcm2)

CPE119877ct

(Ωcm2)119882

(s12Ωcm2)1198840

(s119899Ωcm2) 119899

C10 1898 0002002 08 3296 001104C9 1709 0002221 08 2961 001227C8 1654 0001491 08 260 001459C7 1549 0001598 08 2437 001577C6 164 0001579 08 2235 001505C5 1367 0001895 08 1863 001806

CalculatedMeasured

0 50 100 150 200 250 300 350 400 450 500

300

250

200

150

100

50

0minus119885119894

(Ωcm

2)

119885119903 (Ω cm2)




4 Conclusions




ISRN Corrosion 5




Acknowledgments


References



































6 ISRN Corrosion

























CeramicsJournal of







Biomaterials




Journal of


Journal of


Volume 2014




CoatingsJournal of

Advances in









Volume 2014

MaterialsJournal of

Nano

materials



ISRN Corrosion 5




Acknowledgments


References



































6 ISRN Corrosion

























CeramicsJournal of







Biomaterials




Journal of


Journal of


Volume 2014




CoatingsJournal of

Advances in









Volume 2014

MaterialsJournal of

Nano

materials



6 ISRN Corrosion

























CeramicsJournal of







Biomaterials




Journal of


Journal of


Volume 2014




CoatingsJournal of

Advances in









Volume 2014

MaterialsJournal of

Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of


Volume 2014




CoatingsJournal of

Advances in









Volume 2014

MaterialsJournal of

Nano

materials



an investigation on dislocation density in cold-rolled copper...

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