Thinfilmlubrication andmixedlubricationinnanoscaleLUOJianbinStateKeyLaboratoryofTribologyTsinghuaUniversity,Beijing,China,ContentsIntroductionTestingtechnologyPropertiesofthinfilmlubrication(TFL)FailureoffluidfilmsLubricationmodel&mapContactratioinnano-mixedlubricationConclusion,1.1What’sThinfilmlubrication(TFL)?HDL(1886)EHL(1950s)？BoundaryLurication(1921)Dryslide(Coulomb,1785)1.2Myquestions:What’sthestateoftheregion？What’sitslubricationmechanism?What’stherelationshipbetweensuchregimeandEHLorBoundarylubrication?1.Introduction(1),1.Introduction(2)1.3Jost’squestions(Tribology2000):What’sthedefinitionofboundarylubrication?1.4Granick’squestions(Science,1991)Whatdeterminestheeffectiveviscosityofsuchultra-thinfilm?Whatmakesthefilmchangeintosolidstatefromliquidwhenitisenoughthin?Whydosethesolidfilmcanendueacontinuoussliding？,1.Introduction(3)ExperimentonThinfilmlubrication(TFL)Spikes’sgroup(UK)WenandLuo’sgroup(SKLT,TU,China)Hartal’sgroup(Czechoslovakia)Israelachvili’sgroup(USA)Granick’sgroup(USA)CalculationinTFLTichy,Thompson,Robbins,Hu,Popov,etal.,2.Testingtechnology(1)Measurerange:0~500nmVerticalresolution:0.5nmHorizontalresolution:1mVelocity:0.2~1900mm/sFrictionforceresolution:0.1mNTemperaturerange:~120°CMainQualifications:SchematicofNGY-2,(a)Differentwavelengths(b)DifferentrefractiveindexesResolutionoffilmthicknessv.s.opticalinterferenceintensity2.Testingtechnology(2),Filmthicknessincontactregiona-b-c-d,3.TFLproperties3.1Filmthicknessv.s.influencingfactors3.2Filmthicknessv.s.solidsurfaceenergy3.3EffectofrunningtimeonTFL3.4EffectofexternalelectricfieldonTFL3.5Effectofnano-particlesonTFL3.6TFLviscosity,3.1Filmthicknessv.s.parametersFilmthicknessv.s.viscosityandspeed,FilmthicknesscurveFilmthicknessinthecentralcross-sectionLubricant:mineraloilwithviscosityof36mPa.sat20CTemperature:25C,Diameterofball:20mm,Load:6.05N,A:Decane+3%Palmitic,Load:4N,T=30C,v=0mm/sB:Decane+3%Palmitic,Load:4N,T=30C,v=3.12mm/sC:Whiteoil,Load:20N,T=20C,v=54.5mm/s3.2Effectoftime,FilmthicknesscurveFilmincrosssectionofHertzregionLubricant:Paraffinliquid,Load:Temperature:30ºC,Ball:23.5mmSpeed:18.6mm/sRunningtime:1minSpeed:3.12mm/sRunningtime:40min,Snowball,Lubricant:13604,Load:4N,Temperature:25C3.3Filmthicknesswithsubstrates,3.4TFLunderexternalelectricfieldFilmthicknessv.s.voltageFrictioncoefficientv.s.velocity,EffectofelectricvoltageonTFL,3.5Filmwithnanoparticles(1)EffectofUDPconcentrationonfilmthickness,TimeeffectofUDPconcentrationonfrictionforce3.5Filmwithnanoparticles(2),（a）Whiteoil+0.5%UDP（b）WhiteoilSEMphotosofballsurfaceLoad:4N，Runningtime:30min,3.6EffectiveviscosityofTFL(1)Floatingdeviceforfrictionmeasurement1.Carrierofstraingauge；2.Straingauge；3.Beam;4.Plank；5.Steelball；6.Oilcup;7.MandrilFrictionwithdifferentsubstratesLubrication:paraffinliquid;Load:2NEffectiveviscositywithfilmthickness,Effectiveviscosityv.s.filmthicknessConcentrationofadditive:2%;Load：0.174GPa3.6EffectiveviscosityofTFL(2),4.Thefailureofliquidfilm(1)Filmthicknessv.s.pressureLubricant:PolyglycoloilFilmthicknessv.s.viscosity,(1)L=kv0.69(2)Lf=23.510-4Pf2Failureofliquidfilm:4.Thefailureofliquidfilm(2),5Lubricationmodelandmap(1)HardymodelofboundarylubricationThinfilmlubricationSolidsurfaceFluidmoleculesOrderedmoleculesAdsorbedmolecules,5Lubricationmodelandmap(2)Lubricationmap,v0.69-kp2=0Transitionpoint:Failurepoint:5Lubricationmodelandmap(3),6.Contactratioinnano-mixedlubrication6.1Contactratiov.s.averagefilmthickness;6.2Contactratiov.s.speed,load,lubricantviscosityandpolaradditives;6.3Deformationofasperities;6.4Relationshipbetweenandinfluencefactors.2021/9/3Sept,2001SKLT,TsinghuaUniversity28/18,6.1Contactratioandfilmthickness(a)MaximumHertz(pressure:0.293GPa(b)Lubricant:13604Dynamiccontactratiovs.averagefilmthicknessCombinedsurfaceroughness:16.6nm,6.2Contactratioandinfluencefactors(1)Effectofspeedonthedynamiccontactratio;(2)Effectofloadonthedynamiccontactratio;(3)Effectoflubricantviscosityonthedynamiccontactratio;(4)Effectofsurfaceroughnessonthedynamiccontactratio.2021/9/3Sept,2001SKLT,TsinghuaUniversity30/18,(1)EffectofspeedDynamiccontactratiovs.speedCombinedsurfaceroughness:16.6nm,Lubricant:13604MaximumHertzpressure:0.293GP,(a)v=1.2mm/s,α=0.8(b)v=3.0mm/s,α=0.6(c)v=5.0mm/s,α=0.34(d)v=12.0mm/s,α=0Thefilmthicknessinmixedlubrication(Combinedsurfaceroughness:16.6nm,Lubricant:13604,Pressure:0.293GP),EffectofpressureonthedynamiccontactratioCombinedsurfaceroughness:16.6nm,Lubricant:136042021/9/3Sept,2001SKLT,TsinghuaUniversity33/15(2)Effectofload,(3)EffectofviscosityEffectofviscosityondynamiccontactratioCombinedsurfaceroughness:16.6nm,(4)EffectofsurfaceroughnessRelationbetweencontactratioandsurfaceroughnessLubricant:13604,MaximumHertzpressure:0.293GPa,Fig.10EffectofpolaradditivesoncontactratioCombinedsurfaceroughness:16.6nm，Pressure:0.293GPa(5)Effectofpolaradditives,6.3Deformationofasperities(a)Load:1.2N,=0.08(b)Load:3.6N,=0.24,(c)Load:6.0N,=0.37(d)Load:8.4N,=0.51(e)Load:10.8N,=0.61(f)Load:13.2N,=0.68,(g)Load:15.5N,=0.70(h)Load:17.9N,=0.73(i)Load:20.3N,=0.78Fig.4ContactregionSurfaceroughness:31.7nm,6.4RelationbetweenandinfluencefactorsStaticDynamic,7.Conclusions(1)Thinfilmlubrication(TFL)isanewlubricationregimebetweenboundarylubricationandEHL;InTFL,filmthicknessisnotonlyrelatedtofluidfactors,butalsotothephysicalandchemicalpropertiesofsolidsurfaceandlubricants;InTFL,electricvoltagehasinfluenceonthefilmthicknessinthenanoscale.,7.Conclusions(2)Theincreaseoflubricantviscosityandspeed,theadditionofpolaradditives,andthedecreaseofpressurewillreducethedynamiccontactratio.Thecontactratiobetweentheroughsurfacesislargerthanthatbetweensmoothsurfacesathigherspeed,butitsvaryingrateissmallerthanthatofsmoothsurfaces.,TableofContentsMaterialandTribologicalCharacterizationPhysicalPropertyCharacterizationofMaterialsPeterHodgsonChemicalCharacterizationofMaterialsKazuhisaMiyoshiMechanicalBehaviorofPlastics:SurfacePropertiesandTribologyMarkI.PetrokovetsandNikolaiMyshkinVisualisationandCharacterisationofSurfaceandBulkMorphologyofPolymericMaterialsbyMicrothermalAnalysisandAtomicForceMicroscopyNamitaChoudhuryMacroandMicromechanicsofCeramicsBesimBen-NissanScuffingandSeizureCharacterizationandInvestigationMarianSzczerek,TadeuszBurakowski,andWaldemarTuszynskiWearMappingandFrictionandWearCharacterizationMethodologyS.C.LimandChristinaLimMeasuringTechniqueandCharacteristicsofThinFilmLubricationatNanoScaleLuoJianbinandWenShizhuApplicationTribologyTribologyofMetalCuttingV.AstakhovTribologyofMetalFormingEmilevanderHeideandD.J.SchipperTribologyinTextileManufacturingandUseStephenMichielsenBiotribologyBingShiandHongLiangBiocompatibleMetalsandAlloys:PropertiesandDegradationPhenomenainBiologicalEnvironmentsAlexiaW.E.Hodgson,SannakaisaVirtanen,andHeimoWabussegMeasuringTechniqueandCharacteristicsofThinFilmLubricationatNanoScaleLuoJianbinandWenShizhuItwillbepublishedinApril,2004,Thankyouforattention!,CollisionofaparticletosurfaceParticle：Si，4×4×4crystalcells(512atoms);Surface：Si，22*22*10crystalcells(38720atoms);Insetangel:0º;Speed:50,1200,6000m/s.,Collisionprocess1.Adhesionphenomenon粘着阶段：若入射能量较高，颗粒的势能、热运动能在极短时间内增大到极大值，然后在一段时间内较快地减小，使粘附在表面上的颗粒形成稳定的形态2.Vibrationphenomenon振动阶段：与表面粘着在一起的、具有稳定形态的颗粒上下振动，随着能量的耗散，振幅缓慢减小，振动频率由单晶Si的性质决定,Adhesionprocess(atspeedof50m/s)Adhesionprocesswithin10psPotentialenergy:－Kineticenergy:－Time:0-50ps,Adhesionprocess0-10psAdhesionprocess(atspeedof6000m/s)Potentialenergy:－Kineticenergy:－Time:0-50ps,Vibrationprocessatspeedof1200m/s结合能和颗粒质心位置变化曲线（0～50ps）质心位置：－，结合能：－Vibrationprocess0-50ps振动过程:10~50ps,Vibrationprocess－振动幅度Variationsofparticle’scentralpositionincollisionprocessSpeed:1200m/s,Temperature：300K(－)，50K(－),Vibrationprocess―frequencyVariationsofparticle’scentralpositionincollisionprocess碰撞过程颗粒质心位置变化曲线Insetspeed:1200m/s(－)，6000m/s(－),Thankyouforattention!,为什么粘着？为什么不反弹?若变形颗粒释放的弹性势能小于颗粒与表面的结合能，则发生粘着；反之，颗粒将反弹出表面Si共价键的结合能很大颗粒的粒径越小，能量越易耗散颗粒的粒径越小，结合能越小，越易破碎
