EDM machinability and frictional behavior of ZrO2-WC composi

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IntJAdvManufTechnol(2009)41:1085–1093DOI10.1007/s00170-008-1551-0

ORIGINALARTICLE

EDMmachinabilityandfrictionalbehaviorofZrO2-WCcomposites

K.Bonny&P.DeBaets&J.Vleugels&A.Salehi&O.VanderBiest&http://doc.guandang.netuwers&W.Liu

Received:20December2007/Accepted:28April2008/Publishedonline:7June2008#Springer-VerlagLondonLimited2008

AbstractZirconiumdioxide(ZrO2)-basedcompositeswithWCadditionaredemonstratedtobesuitableforelectricaldischargemachining(EDM)indeionizedwater.ZrO2-basedcompositeswith40vol.%WC,obtainedfromdistinctiveWCpowdersources,wereproducedinordertoderivecorrelationsbetweenmaterialremovalrate(MRR),surfacefinish,wireEDMparametersandmaterialproperties.Dryreciprocatingslidingexperimentsonwire-electricaldis-chargemachinedZrO2-WCcompositesamplesagainstWC-Cocementedcarbide,performedusingapin-on-platetestingrig,revealedasignificantinfluenceofthemicro-structureofthesecondaryWC-phaseonwireEDMbehaviorandfrictionalcharacteristics.

KeywordsZrO2-WCcomposite.Nanocrystalline.Wire-EDM.Surfaceintegrity.Dryreciprocativefriction

1Introduction

Zirconiaceramicshavebeendemonstratedtodisplaythehigheststrengthandtoughnessamongstoxideceramicsduetothestress-inducedphasetransformationfromtetragonaltomonocliniczirconia[1].Combiningthesepropertieswithlowdensityandexcellentresistanceagainsterosion,frictionandthermalshockmakesthesematerialsveryattractiveforawiderangeofapplications[2]inthefieldsofmanufac-turingandcuttingtools[3–6],punches[7],biomedicalapplications[8–12]andevenautomobileandaerospace[13].Themodesthardnessofzirconiahoweverlimitsitsuseinsomeadvancedtribologicalapplications.ElectricallyconductivematerialssuchasWC,TiB2,TiNandTiC0.5N0.5ontheotherhandexhibithighintrinsichardness,butsufferfromlowtoughnessandstrength.Therefore,itwasthoughtthatelectricallyconductivezirconia-basedcompositeswithexcellentstrengthandtoughnessproperties,combinedwithimprovedhardness,couldbeobtainedbytheincorporationofthesesecondaryphasesintothezirconiamatrix[14–19].PreviousinvestigationonZrO2-WCcompositeshasyieldedpromisingresults[20–22].Moreover,thesecondaryphaseofWCrendersthemmanufacturablebysparkerosion,i.e.,electricaldischargemachining(EDM)[23].Oneofthekeyfeaturesofthiselectro-thermalprocessisthepossibilitytomachinecomplexshapesindependentlyofthehardnessofthebasematerial[24,25],makingitveryattractivetobeemployedonengineeringceramics.Moreover,thistechnol-ogyallowsonetooperatewithhighprecisionandonafullautomaticbasis,thussignificantlyreducingproductioncosts.Anumberofresearchinvestigationshavealreadybeenpublishedinthefieldofelectricaldischargemachiningofceramics[26–32]andmoreparticularlyzirconiaceramics[5,33].InthecurrentworkanumberofZrO2-WCcompositeswerecompletelylaboratory-madeusingdistinctiveWC

K.Bonny(*)P.DeBaets

DepartmentMechanicalConstructionandProduction,GhentUniversity(UGent),

IR04,Sint-Pietersnieuwstraat41,B-9000Gent,Belgium

e-mail:koenraad.bonny@UGent.be

J.Vleugels:A.Salehi:O.VanderBiest

DepartmentMetallurgyandMaterialsEngineering,CatholicUniversityLeuven(K.U.Leuven),MTM,KasteelparkArenberg44,B-3001Leuven,Belgium

http://doc.guandang.netuwers:W.Liu

DepartmentMechanicalEngineering,

CatholicUniversityLeuven(K.U.Leuven),PMA,Celestijnenlaan300B,B-3001Leuven,Belgium

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1086startingpowders.FlatsamplesoftheobtainedZrO2-WCmaterialswerein-depthmanufacturedbywireEDM.ThecorrespondingEDMmachinabilityoftwoZrO2-WCgradesunderroughandgraduallyfinerEDMcuttingregimeswascompared.Thecorrelationbetweenmaterialremovalrate(MRR)andwireEDMparameterswaselucidated.Observa-tionsoftopographyandcross-sectionhavebeenperformedandthesurface/sub-surfaceintegritywasanalyzed.

DryslidingexperimentsonflatsamplesoftwoZrO2-WCgradessurfacefinishedbythefinestEDMregimehavebeenexecutedonaPlintTE77tribometerusingWC-Cocementedcarbidepins,withthegoaltodeterminethefrictioncoefficientforbothZrO2-WCgradesand,moreparticularly,toinvestigatetheinfluenceofthesecondaryWC-phaseandloadingconditionsonthefrictionalcharac-teristicsoftheZrO2-WCcomposites.

2Experimentalprocedure

TheZrO2-WCcompositeswereobtainedbyhotpressingamixtureoftwozirconiapowders,i.e.,puremonoclinicZrO2(TosohgradeTZ-0,Japan,crystalsize27nm)and3mol%Y2O3co-precipitatedZrO2(DaiichigradeHSY-3U,Japan,crystalsize30nm),with40vol.%WCpowderand0.75wt.%alumina(BaikowskigradeSM8,France,crystalsize0.6µm)additivebothactingasZrO2graingrowthinhibitorandsinteringaid.TwodifferentWCstartingpowderswereused,i.e.,eitherMBNgradeJ550(Mechano-madenanocrystalline20nmpowderagglomerates<10µm)orEurotungstenegradeCW5000(sub-micrometer-sizeddeagglomeratedWCwithacrystalsizeof0.8–1.0µm).ThetwocorrespondingZrO2-WCgradesarereferredtoas“fine”and“coarse”throughoutthetext.Theyttriastabilizercontentofbothgradeswasfixedat2mol%,asthisamountwasfoundtoresultinthebestcombinationofmechanicalproperties.Moreinformationontheprocessingandcharac-terisationoftheZrO2-WCcompositesisgivenelsewhere[20,21].RepresentativescanningelectronmicrographsofthecoarseandfineZrO2-WCcompositesareshowninFig.1.Themechanicalandphysicalpropertiesofthesecomposites,togetherwithgrain/agglomeratesizeofthesecondaryWCphaseinthecomposites,obtainedusingImagine-ProPlussoftware,arelistedinTable1.Ascanbeseen,theZrO2-WCcompositescombinehightoughnesswithhighhardness.ThefineZrO2-WCcompositehasalowerYoung’smodulus,buthigherhardnessandequalfracturetoughness,comparedtothecoarsegradeZrO2-WCcompos-ite.Itisworthnotingthatthermalconductivitywasmeasuredusingthelaserflashtechnique(AnterFlashline3000,BelgianCeramicResearchCentre,Mons,Belgium).TheWCgrainsizedistributioninthecoarseZrO2-WCgrade,with50%ofthegrainsbeingsmallerthan0.18µmand90%

IntJAdvManufTechnol(2009)41:1085–1093

Fig.1Microstructureof(a)Coarsegradeand(b)FinegradeZrO2-WCcompositeswith40vol.%WC:greyphaserepresentstheZrO2matrix,whitephaseisWC,blackphaseisAl2O3

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