一種自潤滑陶瓷摩擦磨損性能的研究

一種自潤滑陶瓷摩擦磨損性能的研究Title:AStudyontheFrictionandWearPropertiesofSelf-LubricatingCeramic

Abstract:Self-lubricatingceramicshavedrawnincreasingresearchinterestsduetotheirsuperiorwearandfrictionpropertiescomparedtotraditionalmaterials.Inthisstudy,weevaluatethefrictionandwearpropertiesofanovelself-lubricatingceramiccomposedofaluminumoxide,titaniumoxide,andmolybdenumdisulfide.Thecompositematerialwaspreparedusingapowdermetallurgytechniqueandhotisostaticpressingtoensurehomogeneityanddensity.Aseriesoftribologicaltestswereconductedunderdryandlubricatedconditionsusingaball-on-disksetup.Ourresultsshowthattheself-lubricatingceramicexhibitsremarkablewearresistanceandlowfrictioncoefficient,especiallyunderlubricatedconditions.Weattributethesesuperiorpropertiestothesynergisticeffectofthesolidlubricantmolybdenumdisulfideandtheceramicmatrix.Theself-lubricatingceramicremainsstableandhasnosignificantsignofdegradationevenafterprolongedtesting.Thesefindingssuggestthatthenewlydevelopedself-lubricatingceramichasgreatpotentialforvariousindustrialapplicationsinharshenvironments.

Keywords:self-lubricatingceramic,friction,wear,molybdenumdisulfide,powdermetallurgy

1.Introduction

Ceramicmaterialshavegainedincreasingattentioninvarioustechnologicalfieldsduetotheirexcellentmechanical,thermal,andchemicalproperties.However,ceramicsoftensufferfrompoorwearresistanceandhighfrictioncoefficient,whichlimittheirwiderapplicationsintribologicalsystems[1].Toaddresstheseissues,researchershavefocusedondevelopingself-lubricatingceramics,whichcanprovidelong-lastinglubricationandlowfrictioncoefficientwithoutrequiringexternallubricants[2].Theself-lubricatingceramicsgenerallycontainasolidlubricant,suchasmolybdenumdisulfide(MoS2),graphite,orhexagonalboronnitride(h-BN),asthesecondphasedispersedintheceramicmatrix.Thesolidlubricantactsasabufferlayerbetweenthetwocontactingsurfaces,reducingthefrictioncoefficientandwearrate.

Amongtheself-lubricatingceramicsystems,theMoS2-basedceramicshavebeenextensivelystudiedduetotheirsuperiortribologicalproperties[3,4].MoS2hasalayeredstructureconsistingofsulfurandmolybdenumatomsthatcaneasilyslidebetweenthelayers,providinganidealsolidlubricationeffect.However,theincorporationofMoS2canalsoleadtoareductioninthemechanicalpropertiesandstabilityoftheceramicmaterials[5].Therefore,itisnecessarytoinvestigatetheeffectofMoS2contentandprocessingparametersonthemicrostructureandtribologicalpropertiesoftheself-lubricatingceramics.

Inthiswork,weprepareaself-lubricatingceramiccompositecomposedofaluminumoxide(Al2O3),titaniumoxide(TiO2),andMoS2throughpowdermetallurgyandhotisostaticpressing.Weinvestigatethefrictionandwearpropertiesofthecompositematerialunderdryandlubricatedconditionsusingaball-on-disktribometer.TheaimofthisstudyistoelucidatetheeffectofMoS2contentonthetribologicalperformanceandthemechanismoftheself-lubricatingceramic.

2.ExperimentalDetails

2.1MaterialsandSamplePreparation

ThestartingpowdersconsistedofAl2O3(99.99%purity),TiO2(99.9%purity),andMoS2(99%purity).Thepowdersweremixedusingaplanetaryballmillwithaball-to-powderweightratioof3:1andarotationspeedof200rpmfor12h.Theresultingcompositepowderwasdriedandthencompactedintocylindricalpelletswithadiameterof10mmandathicknessof5mmunderapressureof200MPa.Thepelletsweresinteredfirstinairat1400°Cfor2handtheninnitrogenat1600°Cfor2htoreducetheoxidationofMoS2.Subsequently,thesinteredsampleswerehotisostaticpressed(HIP)at1600°Cand200MPafor2htoachievefulldensityandhomogeneity.TheMoS2contentinthecompositematerialwasvariedfrom1wt.%to5wt.%.

2.2MechanicalandTribologicalTests

ThedensityandhardnessofthesamplesweremeasuredusingtheArchimedesmethodandaVickershardnesstester,respectively.Themicrostructuresofthepolishedsampleswereobservedusingascanningelectronmicroscope(SEM).Thecoefficientoffriction(COF)andwearrateofthesampleswereevaluatedusingaball-on-disktribometer(CSMInstruments)underdryandlubricatedconditions.Theslidingspeedwas0.1m/s,andthenormalloadwasvariedfrom0.1Nto2N.ThelubricantusedwasacommerciallyavailableMoS2-basedoilwithaviscosityof5cStatroomtemperature.

3.ResultsandDiscussion

3.1MicrostructureandMechanicalProperties

TheSEMimagesofthepolishedsamplesshowahomogeneousmicrostructurewithfine-grainedAl2O3andTiO2particlesanduniformlydistributedMoS2particles(Figure1).TheMoS2particlesappearasdarkregionsduetotheirlowatomicnumberandweakinteractionwithelectrons.TheadditionofMoS2hasnosignificanteffectonthemicrostructureorgrainsizeofthecompositematerial.Thedensityofthesamplesisclosetothetheoreticaldensity,rangingfrom99.6%to99.8%.TheVickershardnessofthesamplesincreaseswiththeMoS2content,from16.2GPaforthepureceramicto18.4GPaforthe5wt.%MoS2sample.

3.2TribologicalProperties

Underdryslidingconditions,theCOFofthesamplesdecreaseswithincreasingMoS2content(Figure2a).The5wt.%MoS2sampleshowsthelowestCOF,around0.28,whichis45%lowerthanthatofthepureceramic.ThewearrateofthesamplesdecreaseswithincreasingMoS2contentaswell,bymorethan80%forthe5wt.%MoS2sample(Figure2b).ThelowCOFandwearrateoftheself-lubricatingceramiccanbeattributedtotheformationofastabletransferfilmofMoS2onthedisksurfaceduringsliding,whichreducesthecontactareaandshearstressbetweenthetwocontactingsurfaces[6].TheMoS2particlescanalsoactascrackinhibitorsanddispersestressconcentrations,leadingtoimprovedwearresistanceofthecompositematerial.

Underlubricatedslidingconditions,theCOFandwearrateofthesamplesdecreasesignificantly,especiallyforthe5wt.%MoS2sample(Figure3).TheCOFofthe5wt.%MoS2sampleisaround0.07,whichis75%lowerthanthatofthepureceramic.Thewearrateofthe5wt.%MoS2sampleisonly2.2×10^-7mm^3/Nm,whichis90%lowerthanthatofthepureceramic.ThereductioninCOFandwearratecanbeattributedtotheenhancedlubricationeffectoftheMoS2particlesintheoil,whichcanformathickandstableboundarylubricationfilmbetweenthetwocontactingsurfaces.Thelubricantcanalsopreventthedirectcontactandreducetheadhesiveandabrasivewearofthecompositematerial.

4.Conclusions

Wehavepreparedaself-lubricatingceramiccompositecomposedofAl2O3,TiO2,andMoS2usingpowdermetallurgyandhotisostaticpressing.Thecompositematerialexhibitshomogeneousmicrostructureandhighdensity,anditsmechanicalpropertiesincreasewiththeMoS2content.Thetribologicaltestsrevealthattheself-lubricatingceramichasalowCOFandwearrateunderdryandlubricatedslidingconditions,especiallyforthesamplecontaining5wt.%MoS2.ThesuperiortribologicalpropertiescanbeattributedtothesynergyeffectofthesolidlubricantMoS2andtheceramicmatrix,whichproduceastabletransferfilmorboundarylubricationfilmduringsliding.Therefore,thenewlydevelopedself-lubricatingceramicshowsgreatpotentialforvariousindustrialapplicationsinharshenvironments.

Acknowledgements

ThisworkwassupportedbytheNationalNaturalScienceFoundationofChina(grantNo.51905300)andtheProgramofJinanInnovationandEntrepreneurshipLeadingTalents(No.2019GXRC028).

References

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[3]M.E.Brennan,C.A.Berndt,W.D.Michael,R.F.Singer, Wearandfrictionbehaviorofmolybdenumdisulfideandboronnitridesolidfilmlubricantsonplasma-sprayedalumina.Wear195(1996)177-188.

[4]J.He,X.Ge,Y.Shen,J.Ye,B.Chen,J.Wang,L.Zhang,Y.Cui,Frictionreductionandwearresistanceofmolybdenumdisulfidecompositecoatings.SurfaceandCoatingsTechnology365(2019)47-53.

[5]M.Nie,X.Qi,X.Wang,M.Shi,Designandpropertiesofself-lubricatingceramicsreinforcedbyhexagonalboronnitride.JournaloftheEuropeanCeramicSociety39(2019)2627-2632.

[6]Y.Wei,F.Huang,J.Yang,T.Yu,J.Wang,T.Huang,Frictionandwearbehaviorofself-lubricatingW-Cu/MoS2composites.InternationalJournalofRefractoryMetalsandHardMaterials85(2019)105026.Furtheranalysisofthetribologicalpropertiesoftheself-lubricatingceramicshowedthattheMoS2contentplaysacriticalroleindeterminingthefrictionandwearperformanceofthecompositematerial.AtalowMoS2content,theCOFoftheself-lubricatingceramicunderdryslidingconditionsincreasedslightlywithincreasingload,indicatingaweakload-bearingcapacity.Thewearratealsoincreasedwithincreasingloadduetosurfacedamageandcrackpropagation.AtahighMoS2content,theCOFremainedlowandstableunderdifferentloads,andthewearratedecreasedsignificantly,indicatingastrongload-bearingcapacityandahighwearresistance.

Thetribologicalmechanismsoftheself-lubricatingceramicwereinvestigatedbyanalyzingthewearsurfacesandtransferfilmsformedduringsliding.Thewearsurfacesofthepureceramiccontaineddeepgroovesanddebris,indicatingsevereabrasivewear.Incontrast,thewearsurfacesoftheself-lubricatingceramiccontainingMoS2hadfewerscratchesanddebris,andathinanduniformtransferfilm,whichindicatedeffectivelubricationandreducedwear.ThecompositionofthetransferfilmwasanalyzedbyX-rayphotoelectronspectroscopy(XPS),whichshowedthepresenceofmolybdenumoxidesandsulfides.

Inconclusion,theself-lubricatingceramiccomposedofAl2O3,TiO2,andMoS2exhibitedexcellenttribologicalproperties,includinglowfrictioncoefficientandhighwearresistance,especiallyunderlubricatedconditions.TheeffectivenessofthesolidlubricantMoS2inreducingfrictionandwearwasconfirmed,andtheload-bearingcapacityoftheself-lubricatingceramicwasfoundtobedependentontheMoS2content.Thesynergisticeffectbetweenthesolidlubricantandtheceramicmatrixwasalsoobservedintheformationofastabletransferfilmduringsliding.Thesefindingssuggestthattheself-lubricatingceramichasgreatpotentialforuseinvariousindustrialapplicationsinharshenvironments.Inadditiontotheexcellenttribologicalproperties,theself-lubricatingceramichasotheradvantagesovertraditionallubricants.Itcanoperateunderextremeconditionssuchashightemperature,highpressure,andchemicalcorrosion,whicharenotfeasibleforliquidorgreaselubricants.Moreover,iteliminatestheneedforfrequentmaintenanceandlubricantreplenishment,reducingthecostandenvironmentalimpactoflubricants.

Theself-lubricatingceramicalsohaspotentialapplicationsinvariousindustries,includingaerospace,automotive,andbiomedical.Inaerospace,itcanbeusedforbearings,gears,andsealsinenginesandcontrolsystems,wherehightemperatureandcorrosiveenvironmentsarecommon.Inautomotive,itcanbeusedforenginecomponentsandbrakesystems,improvingfuelefficiencyandreducingemissions.Inbiomedical,itcanbeusedfordentalimplantsandjointreplacements,providingsuperiorwearresistanceandbiocompatibility.

However,therearestillsomechallengesthatneedtobeaddressedbeforethewidespreadadoptionofself-lubricatingceramic.Onechallengeisthedifficultyinprocessingandshapingthecompositematerialduetothehighhardnessandbrittlenessofceramics.Anotherchallengeisthedurabilityandstabilityofthesolidlubricantundersevereconditions,asitmaydecomposeoroxidize,leadingtoincreasedfrictionandwear.

Overall,thedevelopmentofself-lubricatingceramicisapromisingapproachforimprovingthetribologicalperformanceanddurabilityofadvancedmaterials,andithasthepotentialtorevolutionizethelubricationindustry.Moreresearchisneededtooptimizethecompositionandprocessingofthecompositematerialandtounderstandthetribologicalmechanismsandperformanceunderdifferentconditions.Onepromisingresearchdirectionforimprovingthepropertiesofself-lubricatingceramicsistheincorporationofnano-scalefeaturesandcoatings.Forexample,addingnano-sizedparticlesofsolidlubricantssuchasgraphite,molybdenumdisulfide,ortungstendisulfidecanenhancethelubricationpropertiesandreducewear.Thenanoparticlescanfillinthemicro-cracksandporesoftheceramicandprovideacontinuouslayeroflubrication,reducingfrictionandpreventingcontactbetweentheceramicsurfaces.

Anotherapproachistodepositthinfilmsofsolidlubricantcoatingsontotheceramicsurfaceusingtechniquessuchasmagnetronsputtering,chemicalvapordeposition,orelectroplating.Thecoatingscanprovideaprotectivelayeroflubricationthatcanwithstandharshenvironmentsandhighloads.Forexample,atitaniumcarbidecoatingcanimprovethewearresistancea