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CVD

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CVD

    CVD

    J.Mater.Sci.Techno1.,Vo1.19No.3,2003

    prenationareaofresintofiberreinforcementisdoubledin 5min.

    f31Whencoldplasmatreatmenttimeis5min,theval

    uesofILSSandbendingstrengthofthecompositeproduced duringRTMreachthemaximum,andtheyareimprovedby 18%and9%,respectively,comparedwiththoseofuntreated samples.

    REFERENCES

    l1J.S.HaywardandB.Harris:CompositeManufacturing,1990 283

    1,161.

    2s.R.wu,G.S.Sheuands.S.Shyu:J.AppliedPolymerScience, 1996,62,1347.

    31G.Nikos:in13thInt.Conf.onCompositeMaterials,2001.in

    Chinese)

    4U.Plawky,M.LondschienandW.Michaeli:J.Mater.Sci?,1996, 31,6043.

    51R.BentrashidandG.C.Tesoro:TextileResearchJ.,1990,62, 1347.

    6WeiQINandZhiqianZHANG:Mater.Sci.Technol?,2001,9, 23.finChinese)

    CVDSiCFiberElectrochemicallyTreatedbyACCurrent KunLUOt,

    NanlinSHIandYapeiZU

    InstituteofMetalResearch,ChineseAcademyofSciences,Shenyang110016,China

ManuscriptreceivedDecember26,2001,inrevisedformMarch5,2002

    ThetensilestrengthofCVDSiCfiberwasremarkablyimprovedbyelectrochemicaIsurfacetreatment.SEManalysesreveaI

    thatACcurrenttreatmentcouldformamorecornpactandcompleteSi02layerthanDCcurrentonthesurfaceoftheSiC

    fiber.whichwasbeneficiaItotheimprovementoftensilestrength.ItwasalsoverifiedthatACcurrentwasmoreeffectivefor

    producinghighperformanceSiCfiberwithSiO2surfacelayerthanDCcurrent.Thefrequencyisasensitiveparameterforthe

    Process;butthesignalsofinputcurrenthadrelativelysmaIIeffectonthetensilestrenIgthofSiCfiber.Afurtherdiscussion

    forthisphenomenonwascompleted.Theproposedoperationalparametersare0.3A,5kHzofsinewaveand91m/hofthe

    receivingraterespectively.

    KEYWORDS:SiCfiber,Electrochemicaltreatment,ACcurrent

    1.Introduction

    TheCVDSCfiberffabricatedbychemicalvapordeposit

    processing),typically100or140mindiameter,offersa.ttrac

    tivecombinationofhighspecifictensilestrength,stiffnessass

    wellaselevatedtemperaturestability.Itiswidelyusedinad

    vancedcompositematerialsl.However.thetensilestrength

    ofCVDSiCfiberdecreasesseriouslywhensomesurfacede

    fectsappear,suchasmicrovoidsandflaws,andtheinherent

    surfacetensionofthefiberalsomakesthefibersomewhat

    sansitivetosurfaceinjuries.Sometimesthetensilestrength

    caD.decreaseto2500MPaorlower[.

    Itiswidelyacceptedthatthetensilestrengthcanbeef-

    fectivelyincreasedbysurfacetreatment.Forexample,the

    tensilestrengthofSiCfibercanreachsohighas3500MPaor

higherifacarboncoatingwasproperlydepositedonthesur

    face,andthisoperationCallbesimultaneouslycompletedin theCVDprocessing.Bynow.almostallcommercialSiCfiber productsarewithcarboncoatingandcanmeetmostoftheir applications.Butinsomespecialcases,thecarboncoating generatesseriousinterfacialreactionswithactivemetalssuch asAlorTimatrix.AccordingtoadiscoveryonSiCrF,/Al compositestwhichbasedontheanalysesofacousticemis- sionandSEM.therewasasevereinterfacialreactionbetween carboncoatingofSiCfibersandAlmatrix.whichwasmost likeabrittlelayerofAl4C3formedanditobviouslyinflu

    encedtheper~rmanceofthecomposites.Onthecontrary, theelectrochemicallytreatedSiCfibersbuiltaratherstrong bindingtoAlmatrix,sincetheSiO2surfacefilmcould1)tufter theinterfacialreaction.Moreover,theSiO2surfacele~yeris alsobelievedtobepropitioustoenhancethebindingbetween SiCfiberandresinmatrix[4J.

    Electrochemicalsurfacetreatmentmaybethemosteffec

    tiveandeconomicwaytoobtaintheSiCfiberwithSiO:jsur

    facelayer.AlthoughaUKpatent[5Jreportedin1972thatthe tensilestrengthofSiCfibercouldbeimprovedfrom2352MPa to2548~3136MPabyelectrochemicaltreatment,thismethod stillhasnotcaughtthecompositeresearcherseyeyet.The mainreasonwasthatthetensilestrengthafterelectrochem

    tPh.D.candidate,towhomcorrespondenceshouldbeaddressed, E-mail:kluo@imr.aE.cn.

    Fig.1Sketchdiagramoftheexperimentalapparatus icaltreatmentwastoolowtofabricateadvancedcomposite materials.Inourpreviouswork,thestrengthwasfurther

improvedfrom2202MPato3519MPat.butitwasstillnot

    competitivewiththecarboncoatedones.Inordertogethigh

    performanceSiCfiberswithSiO2surfacelayer,aspecialde_ signedapparatuswasemployedinourwork,andACcurrent withdifierentinputfrequenciesandsignalswereappliedto continuouslytreattheasreceivedCVDSiCfiber.

    2.Experimental

    AsshowninFig.1,aspecialdesignedapparatuswasam

    ployed,whichconsistedoftwoelectrolyticcellsandaninsula- tivecel1.5wtpctKOHaqueoussolutionworkedaselectrolyte inroomtemperaturethatwasrecycledintotheelectrolytic cellsbyapump.ThepilotCVDSiCfiberwasdrawncon- tinuonslythroughtheapparatus.AHDV7Cpotentiostat

    andafunctiongeneratorTFG8101offeredconstantcurrents

    withdrentsignalsandfrequencies.whichwereappliedon thenickelelectrodesinthetwoelectrolyticcells.Thecurrent wastransferredintotheSiCfiberviatheelectrolyticsolution. ThetensilestrengthtestswerecarriedoutonaTENSILON UTM.II.20testmachinewithacrossheadspeedof2mm/min andagaugelengthof25mmfloreachspeciInen.TheInor

    phologyoftheSiC6berspecimenswasanalyzedbyscanning electricmicroscopy(SEM).

    3.RsultsandDiscussion

    3.jEfc0fACcufrent

    AfterelectrochemcalsurfacetreatmentbyACcurrent,

284J,Mater.Sci.Technol,,Vo1.19No.3,2003

    Table1Improvementoftensilestrengthafterelectrochemicaltreatment

    Fig.2SEMimagesofthefracturemorphologyforthe

treatedSiCfiberspecimens,(a)treatedbyACcLlr

    rent,(b)treatedbyDCcurrent

    Frequency{~ogf)/Hz

    Fig.3Effectoffrequenciesandsignalsontensilestrength thetensilestrengthofCVDSiCfiberincreasedfrom1925 to3910MPawithanincrementof103pctinaverageand adispersionratioof7.7pct(showninTable1).Compared withtheresultofDCcurrentinourpreviouswork[61.theAC currenttreatedfibercouldofferhighertensilestrengthand reliability.

    Itcouldbeexplainedbyfollowin.,_

    $tworeasonsFirstac

    cordingtothereactionmechanismtJfortheanodizationof SiCfiber:

    SiC+4OH=SiO2+C+2H2O+4e

    whichindicatedthattheconcentrationofOHionaround

    thefiberhadagreatinfluenceontheformationofSiO2S1.1r. facelayer.ItcouldbeimaginedthatOHionwouldbecon.

    sumedwhenthefiberworkedasananode,andgeneratedon thesurfaceofcathodeduetothedecompositionofwater. Inputcurrent/A

    Fig.4Effectofinputcurrentontensilestrength Therefore,whenDCcurrentwasapplied,theconcentrationof oHionintheanodiccellwouldgraduallydecreased,which coulddecreasetheemciencyoftheprocess.Howeverwhen ACcurrentwasapplied,theperiodicallyalternationofpolar

    itywouldmaketheconcentrationofOHionapproximately

    constant.Second,onlyoneofthetwoelectrolyticcellswasin useifDCcurrentwasapplied,butbothworkedbyACcur

    rent.Hence,thetreatingtimewasapproximatelydoubled.

    SEManalysesfFig.21verifiedtheassumptionabove. ComparedwithFig.2(b)(thefractureofSiCfibertreated byDCcurrent),Fig.2(a)showedthattheSi02surfacelayer wasmorecompactandcompleteafterthetreatmentofAC current.ThedifierencebetweenSiCandSi02inmolevolume couldproduceasurfacecompressionthatofieredadditional energyconsumptionduringthetensilebreakofSiCfiberand theformationofSiO2surfacelayercouldsmoothenthesur

    faceandhealedsomeinherentdefectssuchasmicroflaws.It hasbeendemonstratedinourpreviousworktJthatthetwo effectsabovewerebothpropitioustotheimprovementofSiC fiber.Apparently,theSiCfibertreatedbyACcurrentin Fig.2(a)wassuperiortothatbyDccurrentinFig.2(b). 3.2Frequencyoftheinputcurrent

    AsshowninFig.3.thetensilestrengthofthetreatedSiC fiberisgreatlyinfluencedbythefrequency.Thereisasharp increasefrom5Hzto5kHz,andabruptlydeclineswhenthe frequencymovesto500kHz.Ontheotherhand,thecurves ofsine(1efty-axis),triangular(righty-axis)andsquare(right yaxis1arerathersimilarfrom5kHzto500kHz.Thatisto say,thefrequencyisasensitiveparameterfortheimprove- mentoftensilestrength.andthesignalsthemselvestakeless eect.Itisclearthatthealternativepolarizationwillin- fluenceafluctuationofOHionaroundthefiber,whichis

    relatedtotheefficiencyoftheanodicprocess.Theinput frequencydeterminesthechangingrateofpolarization.Gen

    erally,arelativelyhigherfrequencyisinfavorofthestability ofoHion,butifitturnstoofast.thereactivetimewould betooshorttomeettheneedofanodicprocess.Thesignals themselveswerenotsosensitivetotheexperimentbecause

    thewayofchargeanddischargecouldnottakegreateffect ontheformationofSiO2surfacelayer.

    3.3Currentdensityandreceivingrate

    Currentdensityandtreatingtimearebothimportantop- erationalparameters.Figure4showedthattherewasapeak correspondingto0.3Aofsinewave,wherethetensilestrength ?芑『uEcmallscm

    何王c00ll?c0

    :cls0=c0

J.Mater.Sci.Techno1.,Vo1.19No.3,2003

    Receivingrate/(m/hl

    Fig.5Effectofreceivingrateontensilestrength ofthetreatedSiCfiberwashigherandmorereliable.Forthe samereason,therateof91m/hinFig.5wasselecteda.qwel1. Bothofthemwereconsideredastheproposedoperational parametersfortheprocessbesidestheinputfrequency. 4.Conclusion

    ThetensilestrengthofCVDSiCfiberisimprovedfrom 1925MPato3910MPaafterelectrochemicalsurfacetreat

    mentbyACcurrent.SEManalysesrevealthatACcurrent treatmentcouldformamorecompactandcompleteSiO2 layerthanDCcurrentonthesurfaceoftheSiCfiber.which isbeneficialtotheimprovementoftensilestrength. 285

    ItisalsoindicatedthatACcurrentismoreeffectivefor producinghighperformanceSiCfiberwithSiO2surfacelayer thanDCcurrent,becauseitcouldnotonlyelongatethetreat

    ingtimeinthespecialdesignedelectrochemicalapparatus,

butalsobeinfavorofthestabilityofOHionaroundthe

    SiCfiber.Thefrequencyisasensitiveparameterforthepro- cess,whichcouldinfluencethefluctuationofOHion.The

    signalofinputcurrenthassmalleffectonthetensilestrength ofSiCfiberintheexperiment.Theproposedoperationalpa- rametersare0.3A,5kHzofsinewaveand91m/hofthe receivingraterespectively.

    Acknowledgement

    Thisworkwassupportedby

    CommitteeofChina(NAMCC)

    0130.

    theNationa1AdvancedMaterials

    withthegrantNo.863-715011

    REFERENCES

    C.M.?rdCloseandJ.G.Robertson:Adv.Perform.Mater.. 1996,3251.

    R.LCraneandV.J.Krukonis:CeramicBulletin,1975,54(2), 184.

    Z.M.ZHoU.N.L.SHI.Z.G.?NGandY.LIANG:AetaMetaJJ.

    Sin.,1996,32(9),1003.(inChinese)

    KunLUo,NanlinSHI,YadingDUAN,YapeiZUandZhiming SHI:AerospaceMater.Techno1.,2001,31(3),45.(inChinese) C.Christan.C.Andre.M.Michel,V.MichelandG.Pierre:UK Patent,No.1269540,1972,4,6.

    KunLUo,NanlinSHI,ZhongshengWEN,YapeiZUandYad- ingDuAN:cn.J.Mater.Res.,2000,14(6),670.(inChi- nese)

    KunLUo,NanlinSHI,YapeiZU,YadingDUANandZhong- shengwEN:Chin.J.Mater.Res.,2001,15(1),105.(in Chinese)

DependenceofStructureandMagneticPropertiesonAnnealing

TemperatureinFe72.

    5Cu1Nb2V28i13.

    5B9Alloy

    ChunyanBA,WenqingGAO,GuiyiZENG,QixianBAandHualinzENG

    SchoolofMaterialsandMetallurgy,NortheasternUniw-rsity,Shenyang110004,China ManuscriptreceivedAugust30,2001,inrevisedformJanuary28,2002

    ThemagneticpropertiesofFe72.

    5CutNb2V2Sil3.

    5B9alloyareinvestigatedfromanamorphoustoananocrystallineandcomplete crystallinestate.Thesampleannealedat550.CforO.5hshowsahomogeneousnanocrystallinestructureandpresentsexcellent

    softmagneticproperties.Whenthespecimenswereannealedatatemperatureabove600.C, themagneticpropertiesare

    obviouslydeterioratedbecausethegrainsizegrowsup,exceedingtheexchangelength. KEYWORDS:Fe72.

    5CulNb2V2Sil3.

    5B9alloy,Softmagneticproperties,Nanocrystallinestructure,Grainsize 1.Introductlon

    Fe-basednanocrystallinematerials,obtainedbyappropri.

    atelyannealingamorphousribbonsabovethecrvstallization temperature,consistofahomogeneousultrafinegrainstruc. tureofo/.FIeSiwithgrainsizesofD?1020nmandsome

    residualamorphousphase.Thisnanostructureleadstotheir

    excellentsoftmagneticproperties,suchashighsaturation

    magnetizationandhighpermeability[.Theformationof

    thenanocrystallinestructureisascribedtothecombinedad. ditionofCuandNb,allofwhicharenotsolublein0Fe.

    TheCuisthoughttoenhancethenucleationof(9/FeSigrain

    whereasNbhindersitsgrowtht5,6J.

AlthoughthenanocrystallineFe73.

    5Cu,Nb3Sil35B9alloy

    hasexcellentmagneticproperties,theamorphousribbonsof thealloyareverybrittle.WhenVpartiallytakestheplace ofNb.thebrittlenessoftheamorphousribbonsisobviously improved.Inthiswork.themagneticpropertiesandthe tLecturer,Ph.D.,towhomcorrespondenceshouldbeaddressed E-maihchyban@sina.com.

    microstructureofalloyannealedatdifferenttemperaturehave beeninvestigated.

    2.Experimental

    Amorphousribbonswiththenormalcompositionof Fen.

    5CulNb2V28i13.5B9(at.pct),10mmwideand35m

    thick,werepreparedbytherapidquenchingtechniqueona singleroller.Forthemeasurementofthemagneticproperties, amorphousribbonsofabout300cmlongwerewoundinto toroidalsampleswithaveragediameter1.8cm.Thesamples wereannealedattemperaturer,abetween450.Cto750.Cfor 0.5hinthevacuum.Ineachcase,thesameheattreatments werealsoappliedtothesampleswhichwere5cmlength. whichwereusedforthemicrostructurestudies. 1.hemicrostructureofthespecimenswasexaminedby RigakuXraydiffractometerwithCuKradiationanda graph[ticmonochromaticcrysta1.Thedirectcurrentmag- neticpropertiesweremeasuredwiththeballisticmethod. ?暑fucIIsc

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