CVD金刚石薄膜在水润滑条件下的摩擦磨损性能研究

CVD金刚石薄膜在水润滑条件下的摩擦磨损性能研究【Abstract】CVDdiamondfilmshaveexcellentmechanicalpropertiesandthermalconductivity.However,underwaterlubricationconditions,theirfrictionandwearperformancearegreatlyreduced.Inthisstudy,thewearbehaviorofCVDdiamondfilmsunderwaterlubricationconditionswasinvestigatedbyusingapin-on-diskfrictionandweartester.TheeffectofdifferentslidingspeedandloadonthefrictionandwearbehavioroftheCVDdiamondfilmswasstudied.TheresultsshowedthatthewearresistanceoftheCVDdiamondfilmsdecreasedsignificantlyunderwaterlubricationconditions,andthewearmechanismofthefilmswasmainlyabrasivewearandadhesionwear.

【Introduction】Diamondhasexcellentmechanicalpropertiessuchashighhardness,highwearresistanceandhighthermalconductivity.CVDdiamondfilmshavebeenwidelyusedinvariousindustrialfieldsduetotheirexcellentperformance.However,whenusedunderwaterlubricationconditions,thefrictionandwearperformanceofCVDdiamondfilmsisgreatlyreduced.Thisismainlyduetotheformationofwaterfilmonthesurfaceofthefilms,whichreducesthecontactbetweenthefilmandthecounterface,resultinginanincreaseinfrictioncoefficientandwearrateofthefilms.Therefore,itisnecessarytostudythefrictionandwearbehaviorofCVDdiamondfilmsunderwaterlubricationconditionstoimprovetheirperformance.

【Experimental】TheCVDdiamondfilmsweredepositedonsiliconsubstratesbyusingahot-filamentchemicalvapordeposition(HFCVD)process.Thepin-on-diskfrictionandweartesterwasusedtomeasurethefrictionandwearbehavioroftheCVDdiamondfilmsunderwaterlubricationconditions.Thefrictioncoefficientandwearrateofthefilmswerecalculatedbyusingtherecordedload-displacementandfrictionforcedata.Thesurfacemorphologychangesandwearmechanismsofthefilmswereobservedbyusingascanningelectronmicroscope(SEM)andtransmissionelectronmicroscope(TEM),respectively.

【Results】ThefrictioncoefficientoftheCVDdiamondfilmsincreasedsignificantlyunderwaterlubricationconditionscomparedwiththatunderdryslidingconditions.Thewearrateofthefilmsincreasedwiththeincreaseofloadandslidingspeed.Thewearmechanismofthefilmswasmainlyabrasivewearandadhesionwear.Theabrasivewearwascausedbytheslidingofhardabrasiveparticlesonthefilms,whiletheadhesivewearwascausedbythebondinganddelaminationofthefilmsduetothestrongadhesionbetweenthefilmsandthecounterfaceunderwaterlubricationconditions.

【Conclusions】TheperformanceofCVDdiamondfilmsunderwaterlubricationconditionsisgreatlyaffectedbytheformationofwaterfilmonthesurfaceofthefilms.Thefrictioncoefficientandwearrateofthefilmsincreasesignificantlyunderwaterlubricationconditions.ThewearmechanismoftheCVDdiamondfilmsunderwaterlubricationconditionsismainlyabrasivewearandadhesionwear.ToimprovetheperformanceofCVDdiamondfilmsunderwaterlubricationconditions,itisnecessarytodevelopnewlubricationsystemsormodifythesurfaceofthefilmstoreducetheadhesionbetweenthefilmsandthecounterface.ToimprovethewearresistanceofCVDdiamondfilmsunderwaterlubricationconditions,variousapproacheshavebeenproposed.Oneapproachistomodifythesurfaceofthefilmstoreducetheirinteractionwithwater.Surfacemodificationtechniquessuchasplasmatreatment,ionimplantation,andchemicaletchinghavebeenusedtochangethesurfacepropertiesofthefilms.Forexample,plasmatreatmentwithO2orN2gascanincreasethehydrophilicityorhydrophobicityofthefilms,respectively.Ithasbeenreportedthathydrophobicsurfaceshavebetterwearresistanceunderwaterlubricationconditionsthanhydrophilicsurfaces.Anotherapproachistousedifferentlubricantstoreducetheinteractionbetweenthefilmsandthecounterface.Forexample,ithasbeenreportedthattheuseofionicliquidsorfluorocarbon-basedlubricantscansignificantlyreducethefrictioncoefficientandwearrateofthefilmsunderwaterlubricationconditions.

Moreover,CVDdiamondfilmscanbecombinedwithothermaterialstoformcompositeswithsuperiorwearresistance.Forexample,CVDdiamondfilmscanbedepositedonmetalsubstrates,whichcanimprovethewearresistanceofthemetalcomponentsunderwaterlubricationconditions.ThecompositescanalsobeformedbyincorporatingothermaterialssuchasnanoparticlesorcarbonnanotubesintotheCVDdiamondfilms.Theaddedmaterialscanfillthegapsbetweenthediamondgrainsandenhancethemechanicalpropertiesofthefilms,whichcanimprovetheirwearresistanceunderwaterlubricationconditions.

Inconclusion,thewearbehaviorofCVDdiamondfilmsunderwaterlubricationconditionsisinfluencedbymultiplefactors,includingtheinteractionbetweenthefilmsandwater,theslidingspeedandload,andthewearmechanism.Variousapproacheshavebeenproposedtoimprovethewearresistanceofthefilms,suchassurfacemodification,lubricationsystemoptimization,andcompositeformation.However,thereisstillmuchroomforimprovement,andfurtherstudiesareneededtodevelopnewmethodstoenhancetheperformanceofCVDdiamondfilmsunderwaterlubricationconditions.AnotherapproachtoimprovingthewearresistanceofCVDdiamondfilmsunderwaterlubricationconditionsistointroducedefectsintothefilms.Ithasbeenreportedthatdefectssuchasvacancies,dislocations,orgrainboundariescanimprovethemechanicalpropertiesofthefilms,includingtheirwearresistance.Thedefectscanactasstressconcentratorsorbarrierlayerstoblockthepropagationofcracks,thusenhancingthetoughnessofthefilms.

Furthermore,themicrostructureofCVDdiamondfilmscanalsoaffecttheirwearbehaviorunderwaterlubricationconditions.Thegrainsizeandorientationofthefilmscaninfluencetheirmechanicalproperties,suchastheirhardness,toughness,andfractureresistance.Forexample,ithasbeenfoundthatCVDdiamondfilmswithsmallergrainsizeorhigherorientationexhibitbetterwearresistanceunderwaterlubricationconditionsthanthosewithlargergrainsizeorlowerorientation.

Besides,thewearresistanceofCVDdiamondfilmscanbeoptimizedbycontrollingthedepositionparameters,suchasthegasmixture,temperature,andpressure.Thedepositionparameterscanaffectthegrowthrate,structure,andpropertiesofthefilms,whichcanultimatelyinfluencetheirwearbehavior.Forinstance,ithasbeenreportedthatincreasingthemethaneconcentrationinthegasmixturecanenhancetheadhesionstrengthandwearresistanceofCVDdiamondfilmsunderwaterlubricationconditions.

Overall,improvingthewearresistanceofCVDdiamondfilmsunderwaterlubricationconditionsrequiresacomprehensiveunderstandingoftheunderlyingmechanismsandoptimizationofvariousfactors,includingthefilmproperties,lubricationsystem,andwearconditions.ThedevelopmentofnewtechniquesandmaterialstoenhancetheperformanceofCVDdiamondfilmsinharshenvironmentscanhavesignificantimplicationsforawiderangeofapplications,suchasmachining,cutting,drilling,andbiomedicalimplants.Inadditiontothefactorsmentionedearlier,surfacemodificationisanotherapproachforimprovingthewearresistanceofCVDdiamondfilmsunderwaterlubrication.Surfacemodificationcanalterthesurfacechemistryormorphologyofthefilms,whichcanaffecttheiradhesion,wettability,andtribologicalbehavior.CommonsurfacemodificationtechniquesforCVDdiamondfilmsincludeplasmatreatment,chemicalfunctionalization,andnanocompositecoating.

Plasmatreatmentinvolvesexposingthefilmstohigh-energyplasmatoinducesurfaceactivation,cleaning,orfunctionalization.Plasmatreatmentcanintroducefunctionalgroups,increasesurfaceroughness,orcreatemicro/nanostructuresonthesurfaceofthefilms,whichcanenhancetheirhydrophilicity,adhesion,ortribologicalperformanceunderwaterlubricationconditions.

Chemicalfunctionalizationinvolveschemicallybondingmoleculesorpolymerstothesurfaceofthefilms,whichcanmodifytheirsurfacepropertiesandimprovetheirinterfacialadhesionwiththelubricant.Forexample,silanizationisacommonmethodforfunctionalizingdiamondfilmswithsilanecouplingagents,whichcanenhancetheirwettabilityandlubricityunderwaterlubricationconditions.

NanocompositecoatinginvolvesdepositingathinlayerofanothermaterialonthesurfaceoftheCVDdiamondfilmstocreateacompositestructure.Thecoatingmaterialcanbeametal,ceramic,polymer,orhybridmaterial,whichcanprovideadditionalpropertiessuchashardness,wearresistance,corrosionresistance,oranti-fouling.Thecoatedfilmscanexhibitsuperiorwearperformancecomparedtouncoatedfilmsunderwaterlubricationconditions,duetothehybridstructureandsyn