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Dealloying

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DealloyingDeallo

    Dealloying

Dec.2008,Volume2,No.12(SerialNo.t3)JournalofMaterialsScienceandEngineering,ISS

    N1934-8959,USA

    ;DealloyingofCuCrFeSialloyanditsinfluencefactor ;SUNQiHal.LIYIIaFI3,PENGGui.rongiZHANGRui-junlLIUJianhual

    ;f,.StateKeyLaboratoryofMetastableMaterialsScienceandTechnology,Yanshan,

    f’ersity,Qinhuangdao066004,China

    ;2.DepartmentofEnvironmentalEngineering,EnvironmentalManagementCollegeofCh

    ina,Qinhuangdao066004,China,

    ;3.DepartmentofEnvironmental&ChemicalEngineering,YanshanUniversity.Qinh

    uangdao066004,China)

    ;Abstract:ThedealloyingbehaviorofCuCrFeSialloyinHC1 ;solutionisinvestigated.TheresultsshowsthatthecontentofCr ;decreasesobviouslyandotherslikeFeandSichangelittleunder ;apropercondition.CuCrFeSialloy’sdechromizationoccurred

    ;attheinterfacebetweenCuphaseandCrphaseinitially.and ;thenextendedinwardtheCr.phasejnsideunti1Crphase ;dissolvedentirely.Thebiggerthesample’sdeformationand

    ;surfaceroughness.theshortertheincubationtimeof ;dechromizationOfCuCrFeSialloy.andthetrendof

    ;dechromizationincreases.Simultaneously.thedeformationcan ;increasethedechromizationrateanddecreasethe

    ;compactibilityofthemicrostructureofthedechromization1ayer. ;Keywords:CuCrFeSialloy;dealloying;surfaceroughness; ;deformation

    ;1.Intr0ductiOn

    ;Cualloyiswidelyusedinocean.chemical

    ;engineering,mechanicalengineering,electricpower ;andotherfieldsforitsexcellentcorrosionresistance, ;goodelectricalandheatconductivity.Thoughthealloy ;hasbeenusedforalongtime.itoftenundertakes

    ;seriouscorrosionandleakageintheearlystageduring ;itsservice.whichlimitsitsapplication.Lotsofresearch ;onthedealloyingofcopperalloyisreported[‘?

    ;,

    ;but

    ;mostofthemareconcentratedondezincicationOf

    ;brassanddeatuminizationofaluminumbronze[4-6]. ;However,studyondechromizationbehaviorofCu

    ;alloyinsolutionshasscarcelybeenreported.Recently,

    ;intheinvestigationonbehaviorofCuCrNiAlalloyin ;Acknowledgement:Thisresearchisfinanciallysupposedby ;theScientificResearchFundofHebeiProvincialEducation ;Department,China(No.Z2007208).

    ;Correspondingauthor:ZHANGRui-jun(1962.),male, ;professor;researchfield:metallicmaterials.

    mail: ;E

    ;Zhango@ysu.edu.ca.

    ;HC1solution.ItlSfoundthatthealloydechrominates ;seriouslyunderpropertemperatureandconcentration[ ;,

    ;whichdecreasesthecorrosionresistanceofthealloy. ;AstheresearchonthecorrosionresistanceofCualloy ;containingCrinsolutionshasbeenattachedgreat ;attention81.andHC1isacOmmonacid.sO

    ;dechromizationcorrosionofCuCrFeSialloyisstudied ;inthisarticle,anditistheeffectsofsurfaceroughness ;andthedeformationonincubationtime,temperature ;andconcentrationofHC1solutionforthealloy ;dealloying,rateofdechromization,andmicrostructure ;ofthedechromizationlayerthatareinvestigated.The ;resultissignificantinprovidingcertainevidenceto ;clarifythefactorswhichhaveinfluenceon

    ;dechromizationandtowidentheapplicationofthe ;alloy.

    ;2.Experiment

    ;ACuCrFeSialloycontaining(massfraction,%) ;50.58Cu,48.43Cr,0.52Fe,0.31Si,and0.16otherswas ;usedtopreparesampleswiththesizeof

    ;5mm~5mm~10mm.Thesamplesweredeformedby

    ;W60omnipotenceexperimentalmachine.andthe ;deformationamountofsampleswas20%.60%and ;80%respectively(therewerecracksinthesurfaceof ;sampleswith80%deformationamount).Allthe ;specimenswererubbedwithl50#,600#,l200#grit ;abrasivepaperseparatelytogainthesurfacewith ;variousroughness,thenpolished,washedwithwater ;anddegreasedwithalcoho1.andthenwereimmersedin ;HClsolutionswithdifferentcOncentratiOnand ;35

    ;De

    ;

    ;a

    ;

    ;HoyingofCuCrFeSiahoyanditsinfluencefactor ;temperature.TestswerecarriedoutinaHHS..12type ;electricthermostaticwatercontainer.Thephenomenon ;ofthisexperimentwassurveyedandtheincubation ;timeofdechromization(fromthebeginningthatthe ;specimensimmersedinsolutiontothetimethat ;bubblesappearedonthesurface),thelowest ;concentrationandtemperatureweremeasuredfor ;variousstatespecimens.

    ;Thedechromizationratewas

    ;calculatedaccordingtothefollowingequation: ;

    ;V:h

    ;t

    ;wherehiSthethicknessofdechromization ;layer(distancefromthesurfacetoobviousinterfaceof ;thematrixstructure),tiSthedechromizationtime ;recordedfromthebeginningofbubbleevolution.Each ;dataistheaverageofthree.Thecorrosionmorphology, ;thecharacteristicsofdechromization,thecomposition ;ofphaseandmicrozonewereobservedandanalyzed

    ;bymeansofADVANTPXP?-381X?-rayfluorescence ;spectrometer,Neophot21metallomicroscope, ;KYKY-2800SEM(withEDS),andD/MAX-rBXRD ;(withgraphitemonochromator,Kczradiation). ;3.Resultsanddiscussion

    ;3.1Incubationtimeanddechromizationrateof ;CuCrFeSialloy

    ;Fig.1showsthemicrostructureOfCuCrFeSialloy. ;ItcanbeseenthatthemicrostructureiScomposedof ;CuphaseandtheirregularCrphasedispersedinCu ;matrix.ThesurfaceofCuCrFeSialloychangestolight ;greyandsilverywhiteparticlesareappearedafter ;immersedinHClsolutionwithlowerconcentration ;andlowertemperatureforaperiodoftime.ByXray

    ;fluorescencespectrometer,thecontentofCuiS ;decreasedandpercentofCrisincreased(asshownin ;Table11.ItcanbefoundthatCrprotrudesmore ;obviouslythanCuphase(asshowninFig.2)after ;immersedinHClsolution.whichindicatesthatCu ;phaseismoreeasilycorroded,comparedwithCrphase ;underthecondition.

    ;36

    ;Fig.1OriginalmicrostructureoftheCuCrNiAIahoy

;Table1Compositionofsample’Ssurfaceon

    ;differentcondition(massfraction,%)

    ;Fig.2CorrosioncharacteristicsofCuCrFeSialloyin ;1.2moHClsolutionsat20?for0.5h

    ;(No-dechromization)

    ;Whilethetemperatureandconcentrationofthe ;HC1solutionareseparatelyraisedtoapropervalue, ;dechromizationtakesplaceafteranincubationtime ;sincetheCuCrFeSialloyiskeptinthesolution,and ;oncethedechromizationtakesplace,itproceeds ;quickly.Alotofbubblesemergeonthespecimen ;surfacewhendechromizationtakesplace,thesolution ;graduallychangestodarkgreen,andthesurfaceofthe ;samplegraduallychangestothecolorofpureCu.The ;XrayfluorescencespectrometerandXRDanalyses ;DealloyingofCuCrFeSialloyanditsinfluencefactor ;indicatethatthecontentofCrphasedecreases ;obviously(asshowninFig.31.Incubationtimeandthe ;dechromizationratechangesignificantlywiththe ;specimenstate,ascanbeseenfromFig.4andFig.5. ;Forincubationtime.itdecreaseswiththeincreaseof ;defQlrmationandsurfaeeroughness.The

    ;dechromizationrateincreaseswiththeincreaseof ;deformation,butchangeslittlewithsurfaceroughness. ;Inaddition.theresultsindicatethatthealloyiSmore ;easilydechromatedwhenthereiScrackonthesurface. ;>,

    ;C

    ;Fig.3Xraydiffractionpatterns

    ;Deformation,5/%

    ;Fig.4Relationshipsbetweendeformationandincubation ;timeofdechromizationofCuCrFeSialloywifhdifferent ;surfaceroughnessin3.4mol/LHCIsolution.at20?

    ;3.6

    ;3.4

    ;32

    ;0

    ;

    ;

    ;3.0

    ;

    ;

    ;2.8

    ;

;

    ;2.6

    ;0206080

    ;Deformation.J/%

    ;Fig.5Relationshipbetweendeformationand ;dechromizationrateofCuCrFeSialloywithdifferent ;surfaceroughnessin3.4moi/LHCIsolution,at20~C ;3.2Effectsofspecimenstateonsolution

    ;concentrationandtemperatureforCuCrFeSialloy ;todechromate

    ;IfriodechromizationiSobservedfromthe ;specimenkeptfor24hoursinHC1solutionundersome ;temperature,itisconsideredthatthespecimencould ;notdechromateunderthecondition.Fig.6andFig.7 ;showrelationshipbetweenconcentrationofHCl ;solutionandthelowesttemperaturewhile ;dechromizationofsamplesundervariousstates.Itcan ;beseenthatthebiggerthedeformation,thelowerthe ;temperatureandconcentrationofthesolutionforthe ;CuCrFeSialloyspecimendechromizationwhenthe ;surfaceroughnessiskeptconstant.Whileforthe ;surfaceroughness.itsincreasewouldresultinthe ;lowertemperatureandconcentrationofthesolutionfor ;dechromization.

    ;37

    ;?0uI一葛0Dj0_|

    ;DealloyingofCuCrFeSiahoyanditsinfluencefactor ;Temperature,T/.C

    ;Fig.6RelationshipbetweenconcentrationofHCIsolution ;andthelowesttemperaturewhiledechromizationof ;sampleswithoutdeformationundergonedifferent ;surfaceroughness(0%deformation)

    ;3.5

    ;2.8

    ;2.1

    ;1.4

    ;0.7

    ;0.0

    ;020406080

    ;Temperature,T/.C

    ;Fig.7RelationshipbetweenconcentrationofHCIsolution ;andthelowesttemperaturewhiledechromizationof ;sampleswithdifferentdegreeofdeformation ;(polishedwith600#sandpaper)

    ;3.3Eflfectsofspecimenstateondechromization ;layermorphologyofCuCrFeSialloy

    ;Fig.8showsthestructureofthedechromization ;layerofCuCrFeSialloy.Itcanbeseenfromthefigure ;thatCuphaseisthemajorstructureofdechromization ;layer.andmanysmallcavitiescanbeobservedonthe ;surfaceofCuphase,whichismuchsmallerthanthatof ;theCrphase.Thesmallcavitiesareconsidered ;resultingfromthedechromization.Itisfoundthatfor ;thealloywithoutdeformation,theCuphaseistight ;38

    ;exceptthesmallcavitiesleftindechromization.While ;f0rthespecimendeformed.1ittlecracksareobserved ;ontheCumatrixphase.Thisindicatesthatdeformation ;couldfacilitatethedefectsproduction,whilethe ;surfaceroughnesshaslittleinfluenceonthetightness ;ofmatrixphase.Forfurtherunderstandingthe ;mechanismofdechromizationoftheCuCrFeSialloy. ;thestructureisobservedfurtherwithSEM.Itisfound ;thatlightwhitesectionobservedaroundtheCrphase ;(Fig.9)isof21.56wt%to41.61wt%Cr,whichismuch ;lowerthanthatofCrphaseof99.89wt%.The

    ;phenomenondemonstratesthattheprocessof ;dechromizationbeginsattheinterfaceofCuphaseand ;Crphase,andspreadgraduallytocenterofCrphasetill ;theCrphasedisappears.ByTEMinFig.10.itcanbe ;seenthatdeformationproducesmanydislocationson ;theCuphase.AUtheresultsindicatethatsurface ;roughnessanddeformationdon’tchangethe

    ;mechanismofdechromization.

    ;Fig.8DechromizationlayermorphologyofCuCrFeSi ;alloyin3.4mol/LHCIsolutionsfor1h.2O.C ;(samplespolishedwith800#sandpaper)

    ;Notes:(a)issamplewithoutdeformation;(b)issampleof ;80%thicknessreduction

    ;-

    ;1..I10舟扫I100I10_101100uI10U

    ;DealloyingofCuCrFeSialloy

    ;a

    ;

    ;nd————

    ;i

    ;——

    ;t

;——

    ;s

    ;————

    ;i

    ;..

    ;n

    ;....

    ;fl————

    ;u

    ;..

    ;e

    ;....

    ;n

    ;....

    ;c

    ;...

    ;e

    ;.....

    ;f...

    ;a

    ;....

    ;c

    ;...

    ;t

    ;...

    ;o

    ;——

    ;r

    ;Fig.9SEMmicrographofdechromizationareaof ;CuCrFeSialloyin3.4mol/LHCIsolutionsfor1h, ;20~C(nodeformationsamplespolished

    ;with800#sandpaper)

    ;Fig.10TEMphotographofCumatrixwith ;80%deformation

    ;3.4Discussion

    ;SincetheCrexposedintheairisveryeasytobe ;oxidized,asteadypassivationfilmgraduallyformson ;thesurfaceanditselectrodepotentialbecomesmore ;positiveafterbeingoxidized;sothedechromizationof ;Cu?Cralloysbecomesdifficultduetopassivation.In ;theHC1solutions,C1’couldtakepartintheanodic

    ;dissolving.Inaddition,becauseofhighpolarityand ;strongpenetrabilityofCI’[9.thepassivationfilmsin ;theCrsurfacearedestroyedwhentheconcentrationof

;CI’reachestoacriticalvalue.Moreover,thehigherthe

    ;concentrationandthetemperature,thegreaterthe ;activationofC1.,whichbenefittotheruptureofthe ;passivationfilm.OncethepassivationfilmontheCr ;surfaceisdestroyed.Crcanbeactivatedandforthe ;activityoftheactivatedCrishigherthanthatofCu,the ;dechromizationtakesplaceimmediately.Theprocess ;canbeillustratedasfollowing:

    ;Anodicaction:CrCr+3e

    ;Cathodeaction:H2eH,

    ;Sincetheatomdiametersandcrystalstructuresof ;theCuandCrphasesaredifferentfromeachother,at ;thebordersofthetwophases,atomarrangementIsnot ;continuous,withmanyholesexisting.Inaddition, ;latticedistortionattheinterfaceisbigger,andthe ;atomsareinhigherenergystateandeasilytransfer ;Outsidefromtheinterface[0..Therefore,the ;dechromizationoccursattheinterfaceofCuandCr ;phaseinitially,andthenextendstotheCrphaseinside ;untiltheCrphasedissolvesentirely.Forthesurface ;roughness,whenthesamples’surfaceispolishedby

    ;sandpapers,thebiggerthesizeofsands(therougher ;thesurface),thedeeperthenicksoftheCrsurface.The ;relativesurfaceareaofCrphaseisbiggerandthenthe ;localdeformationintheCrsurfaceisrelatively ;increased,thedislocationdensityofCrsurfaceis ;increasedtoo,therefore,thetightness,smoothdegree ;andthestabilityofthepassivationfilmontheCr ;surfacearedecreasedwhichfacilitatethepenetration ;ofC1.intothepassivationfilmandacceleratethe ;fractureofthepassivationfilmandshortenthe ;incubationtimeofdechromization.Ontheotherhand, ;deformationcanincreasethelatticedefectsofCr ;passivationfilmandfacilitatethepenetrationofC1and ;thenfacilitatethedechromization.Therefore,the ;biggerthedeformationandtherougherthesurface,the ;passivationfilmwillbemoreunstableandeasytobe ;ruptured~”.whichfacilitatethedechromizationand

    ;shortentheincubationtime.

    ;Inaddition,deformationcanresultinthe

    ;deformationofCuandCrphaseandsubsequentlymore ;cavitiesanddislocationwhichprovidetheconvenient ;channe1forC1’andCrtransference[12-13]and

    ;subsequentlyincreasethedechromizationrate.Forthe

    ;samplewithcracks,thedecreaseindechromization ;rateismoreobvious.Fordeformationinducesstressin ;theCuCrFeSialloy,stresscorrosionandstimulate ;crazecouldtakeplacewhenthealloyinHC1

    ;solution[41.whichresuItsinthecrackanddecreasethe ;39

    ;DealloyingofCuCrFeSiahoyanditsinfluencefactor ;densityofthedechromizationstructure.Whilethe ;roughnessofthesurfacecouldonlyhaveinfluenceon ;stabilityofthepassivationfilmandthushaveinfluence ;onthedechromizationoftheCuCrFeSialloy.andhave ;littleeffectsonthemicrostructure0fCuandCrphase. ;Therefore,theroughnesshaslessinfluenceonthe ;dechromizationrateandstructureofdechromization ;layer.

    ;4.Conclusion

    ;TheCuCrFeSialloycoulddechromizationinHCl ;solutionatapropertemperatureandconcentration ;range.Theincubationtime,thetemperatureand ;concenationofHClsolutionfordechromizationof ;theCuCrFeSialloydecreasewiththeincreaseof ;surfaceroughnessanddeformation.Theroughnessof ;thespecimenhaslittleinfluenceonthedechromization ;rateandthestructureofdechromizationlayer.but ;deformationcouldincreasethedechromizationrate, ;anddecreasethetightnessofthedechromizationlayer. ;References:

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