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FABRICATIONOFPIEZOELECTRICCERAMlClPOLYMERCOMPOSITESBYINJECTIONMOLDING.LeslieJ.BowenandKennethW.French,MaterialsSystemsInc.53HillcrestRoad,Concord,MA01742AbstractResearchattheMaterialsResearchLaboratory,PennsylvaniaStateUniversityhasdemonstratedthepotentialforimprovinghydrophoneperformanceusingpiezoelectricceramic/polymercomposites.AspartofanONR-fundedinitiativetodevelopcost-effectivemanufacturingtechnologyforthesecomposites,MaterialsSystemsispursuinganinjectionmoldingceramicfabricationapproach.Thispaperbrieflyoverviewskeyfeaturesoftheceramicinjectionmoldingprocess,thendescribestheapproachandmethodologybeingusedtofabricatePZTceramic/polymercomposites.PropertiesandapplicationsofinjectionmoldedPZTceramicsarecomparedwithconventionallyprocessedmaterial.IntroductionPiezoelectricceramic/polymercompositesofferdesignversatilityandperformanceadvantagesoverbothsinglephaseceramicandpolymerpiezoelectricmaterialsinbothsensingandactuatingapplications.ThesecompositeshavefounduseinhighresolutionmedicalultrasoundaswellasdevelopmentalNavyapplications.Manycompositeconfigurationshavebeenconstructedandevaluatedonalaboratoryscaleoverthepastthirteenyears.Oneofthemostsuccessfulcombinations,designated1-3compositeinNewnhamsnotationl1,hasaone-dimensionallyconnectedceramicphase(PZTfibers)containedwithinathree-dimensionallyconnectedorganicpolymerphase.Hydrophonefiguresofmeritforthiscompositecanbemadeover10,000timesgreaterthanthoseofsolidPZTceramicbyappropriatelyselectingthephasecharacteristicsandcompositestructure.ThePennStatecompositeswerefabricatedlbyhand-aligningextrudedPZTceramicrodsinajigandencapsulatinginepoxyresin,followedbyslicingtotheappropriatethicknessandpolingtheceramic.Asidefromdemonstratingtheperformanceadvantagesofthismaterial,thePennStateworkhighlightedthedifficultiesinvolvedinfabricating1-3compositesonalargescale,orevenforprototypepurposes.Theseare:11TherequirementtoalignandsupportlargenumbersofPZTfibersduringencapsulationbythepolymer.2)Thehighincidenceofdielectricbreakdownduringpolingarisingfromthesignificantprobabilityofencounteringoneormoredefectivefibersinatypicallargearray.Overthepastfiveyearsseveralattemptshavebeenmadetosimplifytheassemblyprocessfor1-3transducerswiththeintentionofimprovingmanufacturingviabilityandloweringthematerialcost.EarlyattemptsinvolveddicingsolidblocksofPZTceramicintothedesiredconfigurationandback-fillingthespaceswithapolymerphase.Thistechniquehasfoundwideacceptanceinthemedicalultrasoundindustryformanufacturinghighfrequencytransducers2.Morerecently,FiberMaterialsCorp.hasdemonstratedtheapplicabilityofitsweavingtechnologyforfiber-reinforcedcompositestotheassemblyofpiezoelectriccomposites31.Anotherexploratorytechniqueinvolvesreplicatingporousfabricshavingtheappropriateconnectivity41.Forextremelyfinescalecomposites,fibershavingdiametersintheorderof25to100pnandaspectratiosinexcessoffivearerequiredtomeetdeviceperformanceobjectives.Asaresult,thesedifficultiesarecompoundedbytheadditionalchallengeofformingandhandlingextremelyfinefibersinlargequantitieswithoutdefects.Recently,researchersatSiemensCorp.haveshownthatveryfinescalecompositescanbeproducedbyafugitivemoldtechnique.However,thismethodrequiresfabricatinganewmoldforeverypart51.Thispaperdescribesanewapproachtopiezoelectriccompositefabrication,viz:Ceramicinjectionmolding.Ceramicinjectionmoldingisacost-effectivefabricationapproachforbothNavypiezoelectricceramic/polymercompositesandforthefabricationofultrafinescalepiezoelectriccomposites,suchasthoserequiredforhighfrequencymedicalultrasoundandnondestructiveevaluation.Theinjectionmoldingprocessovercomesthedifficultyofassemblingorientedceramicfibersintocompositetransducersbynet-shapepreformingceramicfiberarrays.Asidefromthisadvantage,theprocessmakespossibletheconstructionofcompositetransducershavingmorecomplexceramicelementgeometriesthanthosepreviouslyenvisioned,leadingtogreaterdesignflexibilityforimprovedacousticimpedancematchingandlateralmodecancellation.ProcessDescriotionInjectionmoldingiswidelyusedintheplasticsindustryasameansforrapidmassproductionofcomplexshapesatlowcost.Itsapplicationtoceramicshasbeenmostsuccessfulforsmallcross-sectionshapes,e.g.threadguides,andlarge,complexshapeswhichdonotrequiresinteringtohighdensity,suchasturbinebladecastinginserts.Morerecently,theprocesshasbeeninvestigatedasaproductiontechnologyforheat-engineturbinecomponents6,71.TheinjectionmoldingprocessusedforPZTmoldingisshownschematicallyinFigure1.Byinjectingahotthermoplasticmixtureofceramicpowderandorganicbinderintoacooledmold,complexshapescanbeformedwiththeeaseandrapiditynormallyassociatedwithplasticsmolding.Precautions,suchashard-facingthemetalcontactsurfaces,areimportanttominimizemetalliccontaminationfromthecompoundingandmoldingmachinery.Forceramics,thebindermustberemovednondestructively,necessitatinghighsolidsloading,carefulcontrolofthebinderremovalPowderProcessing-r-4CERAMICPREFORMOrganicBinder-IGranulateI-PREFORMLAY-UPTOFORMLARGERARRAYS-_Lu-i_-1-1andapplyelectrodesFigure1:InjectionMoldingProcessRcess,andproperfixturing.Oncethebinderisremoved,thesubsequentfiring,polingandepoxyencapsulationprocessesaresimilartothoseusedforconventionalPZTipolymercomposites11I.Thus,theprocessoffersthefollowingadvantagesoveralternativefabricationroutes:Complex,nearnet-shapecapabilityforhandlingmanyfiberssimultaneously;rapidthroughput(typicallysecondsperpart);compatibilitywithstatisticalprocesscontrol;lowmaterialwaste;flexibilitywithrespecttotransducerdesign(allowsvariationinPZTelementspacingandshape);andlowcostinmoderatetohighvolumes.Ingeneral,becauseofthehighinitialtoolingcost,theceramicsinjectionmoldingprocessisbestappliedtocomplex-shapedcomponentswhichrequirelowcostinhighvolumes.ComoositeFabricationandEvaluationTheapproachtakentofabricate1-3piezoelectriccompositesisshowninFigure2a,whichillustratesaPZTceramicpreformconceptinwhichfiberpositioningisachievedusingaco-moldedintegralceramicbase.Afterpolymerencapsulationtheceramicbaseisremovedbygrinding.Asidefromeaslngthehandlingofmanyfibers,thispreformapproachallowsbroadlatitudeintheselectionofpiezoelectricceramicelementgeometryforcompositeperformanceoptimization.Tooldesignisimportantforsuccessfulinjectionmoldingofpiezoelectriccomposites.TheapproachshowninFigure2busesshapedtoolinsertstoallowchangesinpartdesignwithoutincurringexcessiveretoolingcosts.Figure2cshowshowindividualpreformsareconfiguredtoformlargerarrays.Figure2a:PreformConfiguration(Approx.400ceramicelements)REMOVABLEINSERT:CAVITYTOOLBODYU*SPRUEFigure2b:InjectionMoldingToolConfigurationFigure2c:LargeAreaCompositeArraysmadefromPreformsFigure2:PreformApproachtoCompositeFabrication.Inpractice,materialandmoldingparametersmustbeoptimizedandintegratedwithinjectionmoldingtooldesigntorealizeintactpreformejectionaftermolding.Keyparametersinclude:PZT/binderratio,PZTelementdiameterandtaper,PZTbasethickness,toolsurfacefinish,andthemoldedpartejectionmechanismdesign.Inordertoevaluatetheseprocessparameterswithoutincurringexcessivetoolcost,atooldesignhavingonlytworowsof19PZTelementseachhasbeenadoptedforexperimentalpurposes.Eachrowcontainselementshavingthreetaperangles(0,1and2degrees)andtwodiameters(0.5andlmm).Toaccommodatemoldingshrinkage,thesizeofthepreformismaintainedat5Ox50mmtominimizethepossibilityofshearingofftheoutermostfibersduringthecoolingportionofthemoldingcycle.Figure3:InjectionMolded1-3CompositePreforms.161Figure3showsgreenceramicpreformsfabricatedusingthistoolconfiguration.NotethatallofthePZTelementsejectedintactaftermolding,includingthosehavingnolongitudinaltaperingtofacilitateejection.Slowheatinginairhasbeenfoundtobeasuitablemethodfororganicbinderremoval.Finally,theburned-outpreformsaresinteredinaPbO-richatmosphereto97-98%ofthetheoreticaldensity.Noproblemshavebeenencounteredwithcontrollingtheweightlossduringsinteringofthesecompositepreforms,evenforthosefine-scale,high-surfaceareapreformswhichareintendedforhighfrequencyultrasound.-.-.L.Figure4:ScanningElectronMicrographsofAs-molded(Upper)andAs-sintered(Lower)SurfacesofPZTFibers.Figure4illustratesthesurfacesofas-moldedandas-sinteredfibers,showingthepresenceofshallowfoldlinesapproximately10pmwide,whicharecharacteristicoftheinjectionmoldingprocess.Thefibersexhibitminorgroovingalongtheirlengthduetoejectionfromthetool.Figure5showsthecapabilityofnearnet-shapemoldingforfabricatingveryfinescalepreforms;PZTelementdimensionsonly30pmwidehavebeendemonstrated.Theas-sinteredsurfaceoftheseelementsindicatesthatthePZTceramicmicrostructureisdenseanduniform,consistingofequiaxedgrains2-3pmindiameter.Figure5:Fine-scale2-2CompositeformedbyNearNet-shapeMolding(UpperMicrograph).As-sinteredSurface(LowerMicrograph).Inordertodemonstratethelay-upapproachforcompositefabrication,compositesofapproximately10volumepercentPZT-5HfibersandSpurrsepoxyresinwerefabricatedbyepoxyencapsulatinglaid-uppairsofinjectionmoldedandsinteredfiberrowsfollowedbygrindingawaythePZTceramicstockusedtomoldthecompositepreform.Figure6showscompositesamplesmadefromfreshly-compoundedPZT/bindermixtureandfromreusedmaterial.Recyclingofthecompoundedandmoldedmaterialappearstobeentirelyfeasibleandresultsingreatlyenhancedmaterialutilization.Table1comparesthepiezoelectricanddielectricpropertiesofinjectionmoldedPZTceramicspecimenswiththosereportedforpressedPZT-5Hsamplespreparedbythepowdermanufacturer.WhenthesinteringconditionsareoptimizedforthePZT-5Hformulation,thepiezoelectricanddielectricpropertiesarecomparableforbothmaterials.Sincethedonor-dopedPZT-5Hformulationisexpectedtobeparticularlysensitivetoironcontaminationfromtheinjectionmoldingequipment,theimplicationofthesemeasurementsisthatsuchcontaminationisnegligibleinthisinjectionmoldedPZTmaterial.*PowdersuppliedbyMorganMatroc,Inc.,Bedford,Ohio;Lot105A.162Table1:PropertiesofInjectionMoldedPiezoelectricCeramics.SpecimenRelativeDielectricd33TYPePermittivityLoss(1kHz1(pC/N)Die-Pressed35840.018745Inj.Molded*35880.018755*Aged24hoursbeforemeasuremegt.*Polingconditions:2.4kV/mm,60C,2minutes.Figure6:InjectionMoldedPZTFiber/EpoxyResinCompositespreparedbythePreformLay-upMethod.SummarvCeramicinjectionmoldinghasbeenshowntobeaviableprocessforfabricatingbothPZTceramicsandpiezoelectricceramic/polymertransducers.TheelectricalpropertiesofinjectionmoldedPZTceramicsarecomparablewiththosepreparedbyconventionalpowderpressing,withnoevidenceofdeleteriouseffectsfrommetalliccontaminationarisingfromcontactwiththecompoundingandmoldingequipment.Byusingceramicinjectionmoldingtofabricatecompositepreforms,andthenlayingupthepreformstoformlargercompositearrays,anapproachhasbeendemonstratedfornet-shapemanufacturingofpiezoelectriccompositetransducersinlargequantities.AcknowledaementsThisworkwasfundedbytheOfficeofNavalResearchunderthedirectionofMr.StephenE.Newfield.TheauthorswishtothankMs.HongPhamfortechnicalassistance,andDr.ThomasShroutoftheMaterialsResearchLaboratory,Penn.StateUniversityforelectricalmeasurements.ReferenceslR.E.Newnhametal,CompositePiezoelectricTransducers,MaterialsinEngineering,Vol.2,pp.93-106,Dec.1980.21C.Nakayaetal,IEEEUltrasonicsSymposiumProc.,Oct.16-18,1985,p634.131S.D.Darrahetal,LargeAreaPiezoelectricComposites,Proc.oftheADPAConferenceonActiveMaterialsandStructures,Alexandria,Virginia,Nov.4-8,1991,Ed.G.Knowles,InstituteofPhysicsPublishing,pp139-142.A.SafariandD.J.Waller,FineScalePZTFiber/PolymerComposites,presentedattheADPAConferenceonActiveMaterialsandStructures,Alexandria,Virginia,Nov.414-8,1991.5U.Bast,D.CramerandA.Wolff,ANewTechniquefortheProductionofPiezoelectricCompositeswith1-3Connectivity,Proc.ofthe7thCIMTEC,Montecatini,Italy,June24-30,1990,Ed.P.Vincenzini,Elsevier,pp2005-2015.G.BandyopadhyayandK.W.French,FabricationofNear-netShapeSiliconNitridePartsforEngineApplication,J.Eng.forGasTurbinesAndPower,108,J.Greimetal,InjectionMoldedSinteredTurbochargerRotors,Proc.3rd.Int.Symp.onCeramicMaterialsandComponentsforHeatEngines,LasVegas,Nev.,pp.1365-1375,Amer.Cer.Soc.1989.61pp536-539,1986.171163制作压电陶瓷/聚合物复合注塑莱斯利J.Bowen和肯尼思W.法国,材料Systems公司53Hillcrest路,康科德,硕士01742摘要在材料研究实验室,宾州州立大学研究已经证明改进水听器表现的潜力使用压电的制陶艺术/聚合物合成物.为这些合成物,材料系统有成本效益的制造业技术正追求一制陶艺术的制造接近注射模塑.本文简要概述主要特征的陶瓷注塑成型工艺,接着介绍的方式和方法可以被用来制造压电陶瓷/聚合物复合材料.性能和应用注塑压电陶瓷与常规加工材料.简介压电的制陶艺术/聚合物合成物给予关于单相陶瓷和聚合物阶段制陶艺术压电的材料在遥感和实际应用两方面设计多技能和表现优势。这些合成物已经在以及发展的海军应用高分辨医学超声中找出使用.在过去13年对许多实验室进行了已建成组合配置和评价.全球最成功的组合,指定1-3复合冈维尔的五线谱l有一个连在尺寸上陶瓷相(压电纤维)控制在一个三维连通有机高分子阶段.水听器人物优异这种复合材料可取得超过一万倍以上的固体压电陶瓷由适当选择的阶段性特征和复合结构在宾夕法尼亚州立复合材料l进行手工调挤压压电陶瓷棒在跳汰及封装环氧树脂,然后切片到适当的厚度和极化的陶瓷.除了展现优越的技术性能,这种材料,在宾夕法尼亚州工作的突出困难,编造1-3复合材料的大规模甚至为原型的目的.这些措施包括:1）把许多的许多PZT纤维排成一排在包装期间经过聚合物和支撑要求.2）2)在滑行期间电介质故障,起源于遭遇在一典型大阵列.中一根或更多有缺陷纤维的重要可能性的高发生.过去五年已做了一些尝试,以简化装配过程1-3传感器与有意提高制造业的可行性,并降低材料成本.早期从事固体切丁块压电陶瓷成为理想的配置和回填土的空间内的一种高分子相.这项技术已广泛接受了超声医学业生产高频传感器2.最近,纤维材料股份有限公司已证明适用其织造工艺纤维复合材料向大会压电陶瓷复合材料3.另勘探技术涉及复制的多孔面料有适当的连通4.为极其好刻度合成物,纤维,大约25到100pn和超过五一个尺寸与另一个尺寸之比有直径需要来遭遇装置表现目标.因此,这些困难被附加挑战用形成没有缺点和处理在大数量中极其好纤维构成了.最近,研究人员在西门子公司已表明很细尺度复合材料可以产生一个逃犯模具技术.但是,这种方法需要制作一个新的模具,每部分5.本文描述了一种新方法,压电复合材料的制备,即:陶瓷注射成型.陶瓷注射成型技术是一种有成本效益的制备方法双方海军的压电陶瓷/聚合物复合材料的制备超细规模压电复合材料,例如那些需要高频医用超声和无损评价.注塑成型过程中,克服困难,装配为主的陶瓷纤维复合成换用网状预成型品陶瓷纤维阵列.除了这方面的优势,这一进程使得有可能建造复合传感器具有更复杂的陶瓷元件几何比原先设想导致更大的灵活性,设计为改进的声阻抗匹配和横向模式取消加工工艺注塑广泛应用于塑料业作为一种手段,快速大量生产,形状复杂,在成本低.应用陶瓷一直最成功的小型截面形状,例如:螺纹指南,及大型复杂形状不需要烧结密度高,如涡轮叶片铸造刀片.最近,这一进程已展开调查,作为生产工艺热发动机涡轮部件6,7图1:注射模塑过程路线.注塑成型用于PZT成型见图1.注的热点热塑性混合陶瓷粉及有机结合成一个冷却结晶复杂的形状,可以形成与方便与快捷通常与塑料成型.防范措施,如硬面临的金属接触面,这些都是重要的,以尽量减少金属污染的加剧和成型机器.陶瓷的粘结剂必须拆除非破坏性地,使成为必要高固体量,严格控制粘结剂,拆除过程中,和正确装夹.一旦粘结剂是拆掉,随后射击极化和环氧包封过程类似于常规pzti聚合物复合1.因此,过程具有以下优点替代加工路线:复杂近净形能力处理许多纤维同时发生;快速吞吐量(通常每秒);兼容性与统计过程控制;低的材料浪费;灵活应变传感器设计(允许变化压电元件间距和形状);成本低,在中度到高度卷.总的来说,由于高的初始成本,工装,陶瓷注射成型是最好的应用复杂形状零件需要低成本高产量制造和评价采取这种办法,编造1-3压电复合载在图2a,它说明了压电陶瓷预制棒的概念,光纤定位是实现以共同塑造积分陶瓷基地.聚合物后封装在陶瓷拆除磨.除了处理许多纤维这预制棒做法使广大纬度在选择压电陶瓷元件几何形状的综合性能优化.工具的设计是成功的重要注塑压电陶瓷复合材料.办法列于图2b用途形工具刀片允许改变部分设计,又不过分更换工具成本.图2c显示了个体预制棒配置,能够形成较大的阵列图2:预制棒的方法综合加工.在实践中,材料成型参数必须优化整合注塑模具设计实现完整的预制弹射后成型.关键参数,包括:压电/粘合剂比,压电元件直径和锥形,基地PZT的厚度,刀具表面光洁度,而塑造的一部分弹射机制设计.为了评价这些工艺参数,又不过分工具成本工具设计,仅有两排19PZT的每一分子已经通过实验目的.每一行包含有三个(0,1和2度)和两个直径(0.5lmm).容纳成型收缩,大小坯维持在5ox50mm以尽量剪过的最外层纤维在冷却部分的成型周期.图3:注射塑造1-3混合成的预成型品.图3显示绿色陶瓷预制装配使用此工具配置.看到所有的PZT分子赶出完好无损后成型,包括具有无纵一端渐渐变细变尖方便弹射.慢热空气已被认为是一种合适的方法有机结合搬迁.最后,烧出预制棒烧结在气氛97-98%的理论密度.没有遇到任何问题与控制体重烧结过程中,这些组合坯即使是这些优秀的尺度,比表面积高预制棒是为高频超声波.图4:扫描电子显微镜对所塑造(上)以及烧结(下)面压电纤维.图4说明了表面为成型和烧结纤
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