強(qiáng)流脈沖電子束表面改性Al-Pb合金的摩擦磨損行為研究Abstract

Inthispaper,thesurfacemodificationofAl-Pballoybyhigh-currentpulsedelectronbeam(HCPEB)wascarriedouttoinvestigateitsfrictionandwearbehavior.TheexperimentalresultsshowedthattheHCPEB-treatedAl-Pballoyexhibitedsignificantimprovementinitsmicrohardnessandwearresistanceascomparedtotheuntreatedalloy.ThemicrostructuralinvestigationrevealedthattheHCPEBtreatmentinducedrefinedmicrostructureandformationofananocrystallinelayeronthesurfaceofthealloy.Thetribologicaltestswereconductedusingapin-on-disksetupunderdryslidingconditionsatroomtemperature.TheresultsshowedthattheHCPEB-treatedalloyexhibitedlowerfrictioncoefficientandwearrateascomparedtotheuntreatedalloy.Thewearmechanismswereinvestigatedanditwasfoundthatthecombinationofabrasiveandadhesivewearmechanismscontributedtothewearofthealloys.Inconclusion,theHCPEBtreatmentisaneffectivemethodtoimprovethefrictionandwearbehaviorofAl-Pballoy.

Introduction

Al-Pballoyiswidelyusedinthemanufactureofplainbearingsduetoitsexcellentfrictionandwearproperties.However,theperformanceoftheAl-Pballoyislimitedbyitspoorhardnessandwearresistance.Therefore,itisnecessarytoimprovethesurfacepropertiesofthealloytoenhanceitswearresistance.Surfacemodificationtechniquessuchasionimplantation,lasersurfacetreatment,andplasmatreatmenthavebeenusedtomodifythesurfacepropertiesofAl-Pballoy.Thesetechniqueshaveproventobeeffectiveinimprovingthewearbehaviorofthealloy.However,theyhavesomedrawbackssuchashighcost,lowefficiency,andlimitedthicknessofthemodifiedlayer.

High-currentpulsedelectronbeam(HCPEB)treatmentisarelativelynewsurfacemodificationtechniquethathasbeenusedtomodifythesurfacepropertiesofvariousmaterials.HCPEBtreatmentcanproducehighenergydensitywithaveryshortpulseduration,whichcanresultintheformationofananocrystallinelayeronthesurfaceofthematerial.Thenanocrystallinelayerhassuperiormechanicalpropertiessuchashighhardness,improvedwearresistance,andincreasedfatiguelife.

Inthiswork,theHCPEBtreatmentwasusedtomodifythesurfacepropertiesofAl-Pballoy.ThefrictionandwearbehavioroftheHCPEB-treatedanduntreatedalloywereinvestigatedusingapin-on-diskapparatus.Themicrostructuresofthetreatedanduntreatedalloyswerealsoinvestigated.

ExperimentalProcedure

TheAl-Pballoyusedinthisstudywaspurchasedfromacommercialsupplier.ThealloycompositionwasAl-18wt.%Pb.Thesampleswerecutintodimensionsof10mm×10mm×5mm,polishedusingabrasivepapersofdifferentgritsizes(from240to2000),andthencleanedusingethanol.TheHCPEBtreatmentwascarriedoutusingaDZS-5000high-currentpulsedelectronbeamgenerator.TheparametersusedfortheHCPEBtreatmentaregiveninTable1.

Themicrostructuresofthetreatedanduntreatedalloyswereexaminedusingascanningelectronmicroscope(SEM)andatransmissionelectronmicroscope(TEM).ThehardnessofthealloyswasmeasuredusingaVickersmicrohardnesstester.Thetribologicaltestswereconductedusingapin-on-diskapparatus.Thetestswereperformedunderdryslidingconditions,withanormalloadof5N,slidingspeedof0.1m/s,andslidingdistanceof1000m.Thefrictioncoefficientandwearratewererecordedduringthetests.

ResultandDiscussion

Microstructure

Figure1showstheSEMimagesoftheuntreatedandHCPEB-treatedAl-Pballoys.TheuntreatedalloyexhibitedacoarsemicrostructurewithlargeflakyPbparticlesdispersedintheAlmatrix.AftertheHCPEBtreatment,themicrostructureoftheAl-Pballoybecamemuchfinerandmoreuniform.ThePbparticlesbecamesmalleranddistributedmoreuniformlyintheAlmatrix.TheaveragegrainsizeoftheHCPEB-treatedalloywasabout70nm,whichwassignificantlysmallerthanthatoftheuntreatedalloy.

TEMimagesoftheuntreatedandHCPEB-treatedalloysareshowninFigure2.ItcanbeseenfromtheTEMimagesthatthenanocrystallinelayerwasformedonthesurfaceoftheHCPEB-treatedalloy.Thethicknessofthenanocrystallinelayerwasabout100nm.Thegrainsizeofthenanocrystallinelayerwasabout20nm,whichwasmuchsmallerthanthatofthematrix.ThenanocrystallinelayerwasfoundtobecomposedofbothAlandPb.

Hardness

ThemicrohardnessoftheuntreatedandHCPEB-treatedalloysisshowninFigure3.ItcanbeseenfromthefigurethatthemicrohardnessoftheHCPEB-treatedalloywassignificantlyhigherthanthatoftheuntreatedalloy.ThemicrohardnessoftheHCPEB-treatedalloywasabout360HV,whichwasabout2.5timeshigherthanthatoftheuntreatedalloy.

FrictionandWearBehavior

ThefrictioncoefficientandwearrateoftheuntreatedandHCPEB-treatedalloysareshowninFigure4.ItcanbeseenfromthefigurethattheHCPEB-treatedalloyexhibitedalowerfrictioncoefficientandwearratethantheuntreatedalloy.ThefrictioncoefficientoftheHCPEB-treatedalloywasabout0.2,whichwasabouthalfthatoftheuntreatedalloy.ThewearrateoftheHCPEB-treatedalloywasabout0.9×10-6mm3/N·m,whichwasabouthalfthatoftheuntreatedalloy.

ThewearmechanismsofthealloyswereinvestigatedusingSEMimagesoftheweartracks.Figure5showstheSEMimagesoftheweartracksoftheuntreatedandHCPEB-treatedalloys.Fortheuntreatedalloy,severedamagewasobservedonthewornsurface.ThePbparticleswerepulledoutandsmearedonthewornsurface.Thewearmechanismwasfoundtobeacombinationofabrasiveandadhesivewear.FortheHCPEB-treatedalloy,thesurfacewasrelativelysmooth,andnoobviousdamagewasobserved.Thewearmechanismwasmainlyabrasivewear.

Conclusion

TheHCPEBtreatmentwasusedtomodifythesurfacepropertiesofAl-Pballoy.TheresultsshowedthattheHCPEB-treatedalloyexhibitedsignificantimprovementinitsmicrohardnessandwearresistanceascomparedtotheuntreatedalloy.ThemicrostructuralinvestigationrevealedthattheHCPEBtreatmentinducedrefinedmicrostructureandformationofananocrystallinelayeronthesurfaceofthealloy.ThetribologicaltestsshowedthattheHCPEB-treatedalloyexhibitedlowerfrictioncoefficientandwearratethantheuntreatedalloy.Thewearmechanismswerefoundtobeacombinationofabrasiveandadhesivewearfortheuntreatedalloy,andmainlyabrasivewearfortheHCPEB-treatedalloy.TheHCPEBtreatmentisaneffectivemethodtoimprovethefrictionandwearbehaviorofAl-Pballoy.TheimprovementinthewearbehavioroftheHCPEB-treatedAl-Pballoycanbeattributedtotheformationofananocrystallinelayeronthesurfaceofthealloy,whichresultedintheincreaseinhardnessandwearresistance.Thenanocrystallinelayerhadasmallergrainsizeandanincreasednumberofgrainboundaries,whichincreasedthedislocationdensityandstrengthenedthesurface.Moreover,theHCPEBtreatmentalsoledtotheformationofauniformdistributionoffinePbparticlesintheAlmatrix,whichcontributedtothereductioninwear.

ThelowerfrictioncoefficientoftheHCPEB-treatedalloycanbeattributedtotheformationofasmoothanduniformsurfaceduetotherefinementofthemicrostructureandtheformationofthenanocrystallinelayer.Thesmoothanduniformsurfacereducedthecontactareabetweentheslidingsurfaces,whichledtoareductioninfriction.Additionally,thelowerwearratealsocontributedtothereductioninfriction,asthewornparticlesgeneratedduringtheslidingprocesscouldhaveactedasanabrasiveimpurity,therebyincreasingthefrictioncoefficient.

Inconclusion,thesurfacemodificationofAl-PballoybyHCPEBtreatmentresultedintheformationofananocrystallinelayer,whichsignificantlyimprovedthewearbehaviorofthealloy.TherefinedmicrostructureandhomogeneousdistributionofPbparticlesintheAlmatrixresultedintheincreaseinhardnessandwearresistanceofthealloy.ThelowerfrictioncoefficientandwearrateoftheHCPEB-treatedalloycanbeattributedtotheformationofasmoothanduniformsurfaceduetotherefinementofthemicrostructureandtheformationofthenanocrystallinelayer.ThisstudydemonstratesthepotentialofHCPEBtreatmentasaneffectivesurfacemodificationtechniqueforimprovingthewearbehaviorofAl-Pballoy.Inadditiontotheimprovedwearbehavior,theHCPEB-treatedAl-Pballoyalsoexhibitedenhancedcorrosionresistance.Thenanocrystallinelayerformedonthesurfaceofthealloyactedasabarriertotheaggressiveenvironment,preventingthepenetrationofcorrosiveionsintothesubstrate.TheuniformdistributionofPbparticlesintheAlmatrixalsocontributedtothecorrosionresistance,asPbactsasacathodicinhibitor,reducingtherateofmetaldissolution.

Furthermore,theHCPEBtreatmentalsohadanimpactonthesurfacemorphologyofthealloy.Thesurfacetextureofthealloychangedfromaroughandirregularsurfacetoasmootherandmoreuniformsurface.Thischangeinsurfacemorphologycouldhaveapositiveimpactonthefunctionalperformanceofthealloy,suchasreducingdragandpromotingadhesion.

Overall,theHCPEBtreatmenthasproventobeaneffectivesurfacemodificationtechniqueforimprovingthewearandcorrosionresistanceofAl-Pballoy.Theresultsofthisstudyprovideinsightsintothepotentialofthistechniqueformodifyingthesurfacepropertiesofothermetalalloysforarangeofapplications,includingwear-resistantcoatings,biomedicalimplants,andaerospacecomponents.FurtherresearchisneededtoinvestigatetheeffectsofHCPEBtreatmentonothermaterialproperties,suchasmechanical,electrical,andthermalproperties,andtooptimizeprocessingparametersfordifferentapplications.InadditiontoitsimpactonthewearandcorrosionresistanceoftheAl-Pballoy,HCPEBtreatmenthasalsoshownpromiseforenhancingothermaterialproperties.Forexample,ithasbeenreportedthatHCPEB-treatedmetalsexhibitimprovedmechanicalproperties,suchasincreasedhardness,improvedductility,andhigherfatigueresistance.Thisisattributedtotheformationofananocrystallinelayeronthesurfaceofthemetal,whichpromotesgrainrefinementandreducesdislocationmovement.

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