improvingsite5

Pleasecitethisarticleinpressas:W.
Dai,etal.
,Microstructureandpropertyofdiamond-likecarbonlmswithAlandCrco-dopingdepositedusingahybridbeamssystem,Appl.
Surf.
Sci.
(2015),http://dx.
doi.
org/10.
1016/j.
apsusc.
2015.
11.
025ARTICLEINPRESSGModelAPSUSC-31742;No.
ofPages7AppliedSurfaceSciencexxx(2015)xxx–xxxContentslistsavailableatScienceDirectAppliedSurfaceSciencejournalhomepage:www.
elsevier.
com/locate/apsuscMicrostructureandpropertyofdiamond-likecarbonlmswithAlandCrco-dopingdepositedusingahybridbeamssystemWeiDaia,,JingmaoLiua,DongsenGenga,PengGuob,JunZhengc,QiminWanga,aSchoolofElectromechanicalEngineering,GuangdongUniversityofTechnology,Guangzhou510006,PRChinabKeyLaboratoryofMarineMaterialsandRelatedTechnologies,ZhejiangKeyLaboratoryofMarineMaterialsandProtectiveTechnologies,NingboInstituteofMaterialsTechnologyandEngineering,ChineseAcademyofSciences,Ningbo315201,PRChinacScienceandTechnologyonSurfaceEngineeringLaboratory,LanzhouInstituteofPhysics,Lanzhou730000,PRChinaarticleinfoArticlehistory:Received14July2015Accepted3November2015AvailableonlinexxxKeywords:Diamond-likecarbonAl:Crco-dopingResidualstressElasticrecoveryTribologyabstractDLClmswithweakcarbideformerAlandcarbideformerCrco-doping(Al:Cr-DLC)weredepositedbyahybridbeamssystemcomprisingananode-layerlinearionbeamsource(LIS)andhighpowerimpulsemagnetronsputteringusingagasmixtureofC2H2andArastheprecursor.
ThedopedAlandCrcontentswerecontrolledviaadjustingtheC2H2fractioninthegasmixture.
Thecomposition,microstruc-ture,compressivestress,mechanicalpropertiesandtribologicalbehaviorsoftheAl:Cr-DLClmswereresearchedcarefullyusingX-rayphotoelectronspectroscopy,transmissionelectronmicroscopy,Ramanspectroscopy,stress-tester,nanoindentationandball-on-platetribometerasfunctionoftheC2H2frac-tion.
TheresultsshowthattheAlandCrcontentsinthelmsincreasedcontinuouslyastheC2H2fractiondecreased.
ThedopedCratomspreferredtobondwiththecarbonwhiletheAlatomsmainlyexistedinmetallicstate.
StructuremodulationwithalternatemultilayerconsistedofAl-poorDLClayerandAl-richDLClayerwasfoundinthelms.
ThoseperiodicAl-richDLClayerscaneffectivelyreleasetheresidualstressofthelms.
Ontheotherhand,theformationofthecarbidecomponentduetoCrincorporationcanhelptoincreasethelmhardness.
Accordingly,theresidualstressoftheDLClmscanbereducedwithoutsacricingthelmhardnessthoughco-dopingAlandCratoms.
Furthermore,itwasfoundthattheperiodicAl-richlayercangreatlyimprovetheelasticresilienceoftheDLClmsandthusdecreasesthelmfrictioncoefcientandwearratesignicantly.
However,theexistenceofthecarbidecomponentwouldcauseabrasivewearandthusdeterioratethewearperformanceofthelms.
2015ElsevierB.
V.
Allrightsreserved.
1.
IntroductionMetal-containingdiamond-likecarbon(Me-DLC)lmshaveattractedagreatdealofresearchattentionowingtotheirexcellentmechanical,tribologicalandbiologicalproperties[1–3].
Further-more,comparingtopureDLClms,Me-DLClmsexhibitrelativelylowinternalstressandhighadhesionstrength[4–6].
Sofar,numerousMe-DLCwithdopingdifferentmetalatomshavebeendepositedusingvarioustechniques.
Itwasreportedthatthedopedmetalatomscouldcreateatwo-dimensionalarrayofnano-clusterswithintheDLCmatrixoranatomic-scalecompositedissolvingintheDLCmatrix,andthechemicalstateandexistenceformofthedopedmetalatomswouldpronouncedlyinuencethepropertiesoftheDLClms[7,8].
Forinstance,whentheweakcarbideformeratoms,likeAl[5]andAg[6],wereincorporatedintoDLC,theytendedtoformductilemetalphaseswithoutbondingwithC.
TheseCorrespondingauthors.
E-mailaddresses:popdw@126.
com(W.
Dai),qmwang@gdut.
edu.
cn(Q.
Wang).
softmetallicphasesimbeddedinthecarbonmatrixcaneffectivelyimprovedtoughnessandreleasedinternalstressviatheplasticdeformation.
However,thesoftandductilemetalphaseswouldalsocausethelmhardnesstodecrease.
Ontheotherhand,thecarbideformers,likeTi[4]andW[9],wouldbondwithCandformhardcarbidephaseinthecarbonmatrixwhentheyweredopedintotheDLC.
Thehardcompositecansignicantlyimprovethehardnessofthelms.
Nevertheless,theformationofMeCbondlengthwouldincreasethedisorderdegreeofthecarbonmatrixandthuscausetheresidualstresstoincrease.
Inaddition,theincreaseofthehard-nesswouldlimittheplasticityanddecreasethetoughnessofthelms.
ItisverydifculttoacquireaDLClmswithacombinationpropertyofhighhardnessandtoughness,andlowinternalstressviadopingonekindofweakcarbonformermetalatomsorcarbideformermetalatoms.
Nevertheless,theco-dopingofcarbideformerandweak-carbideformermetalatomshasbeenexpectedtobeagoodwayforimprovingtheDLClms[10,11].
Inthispaper,DLClmswiththeco-incorporationoftheweakcarbideformerAlandcarbideformerCr(Al:Cr-DLC)weredepositedusingahybridbeamssourcecomprisingananode-layerlinearhttp://dx.
doi.
org/10.
1016/j.
apsusc.
2015.
11.
0250169-4332/2015ElsevierB.
V.
Allrightsreserved.
Pleasecitethisarticleinpressas:W.
Dai,etal.
,Microstructureandpropertyofdiamond-likecarbonlmswithAlandCrco-dopingdepositedusingahybridbeamssystem,Appl.
Surf.
Sci.
(2015),http://dx.
doi.
org/10.
1016/j.
apsusc.
2015.
11.
025ARTICLEINPRESSGModelAPSUSC-31742;No.
ofPages72W.
Daietal.
/AppliedSurfaceSciencexxx(2015)xxx–xxxionbeamsource(LIS)andhighpowerimpulsemagnetronsput-tering(HIPIMS)whichcansignicantlyincreasetheionizationrateandenergyofthespeciesforthegrowthlmsascomparedtotheDCmagnetronsputtering(DCMS)[12].
Thecomposition,microstructure,internalstress,mechanicalpropertiesandtribo-logicalbehaviorsofthelmswerestudiedasafunctionoftheC2H2fractionwhichwasusedtocontroltheAlandCrcontentsinthelms.
Therelationshipsbetweenthemicrostructure,inter-nalstress,mechanicalpropertiesandtribologicalbehaviorswerediscussedindetail.
2.
ExperimentaldetailsSilicon(100)wafersofthicknessat525±15mwereusedasthesubstrates,whichwerecleanedultrasonicallyinacetone,ethanol,anddriedinairbeforebeingputintothevacuumcham-ber.
TheAl:Cr-DLClmswerepreparedbythehybridbeamssystemwhichconsistsoftheLISandtheHIPIMSequippedwithaAlCr(Al/Cr=70/30at.
%)revolvingtarget(purity99.
99%).
Priortodepo-sition,thesubstratesweresputter-cleanedfor20minusingArionsbytheLISatabiasvoltageof300V.
Thebasepressurewasevac-uatedtothevacuumof3*105Pa.
Duringdepositingprocess,thepressurewaskeptatabout0.
5Pa,andthesubstrateholderrotationspeedwassetat4rpm.
AgasmixtureofC2H2andArwasintroducedintothechamberasthegasprecursor.
ThemetalcontentsofAlandCrinthelmswerecontrolledbyvaryingtheC2H2fractionintheprecursorgasesandthetotalgasux(ArandC2H2)waskeptat100sccm.
TypicalvalueoftheLISpowerwas1kW(400Vand2.
5A).
FortheHIPIMSunit,anaveragetargetpowerof2kWwasmaintainedforallexperiments.
Thetargetpeakvoltagewaskeptaround655V.
Thepulserepetitionfrequencywas300Hzandthepulsewidthwasapproximately100s(3%dutycycle).
Abiasvolt-ageof100Vwasappliedtothesubstrate.
Thewholedepositionprocess-timewas2h.
Thethicknessesofthedepositedlmsweremeasuredbyacross-sectionSEM(NovananoSEM430,FEI)measuringscale,andthelmthicknessesarerangingfrom2.
5mto3m.
AnX-rayphotoelectronspectroscopy(XPS,ThermoESCALAB250Xi)withAl(mono)K(hv=1486.
6eV)wasusedtocharacterizethechemi-calcompositionandchemicalbondsofthedepositedlms.
TheXPSenergystepsizewas0.
05eVforthehigh-resolutionspectrums.
Beforecommencingthemeasurement,Ar+ionbeamwasusedtoetchthesamplesurfacefor5mintoremovecontaminants.
ThecontentsoftheelementsinthelmswerecalculatedaccordingtotheatomicsensitivityfactorsandtherelativearearatiosofthepeaksinXPSspectraofthelms.
Andthehydrogenconcentra-tioninthelmswasneglectedduetothelackofsignalintensityinthecurrentXPSdetectionmeasurement.
High-resolutiontransmis-sionelectronmicroscopyofthelmswasperformedonFEITecnaiG2F20S-Twinmicroscopewitha200kVaccelerationvoltage.
TheTEMspecimenwerepreparedbymechanicalpolishingandpreci-sionionpolishingsystem(GatanPIPS691).
ThecarbonatomicbonddetailsofthelmswerecharacterizedusingRamanspectroscopywithincidentlightfromaAr+laseratawavelengthof514.
5nm.
Mechanicalpropertiesweremeasuredbythenano-indentationtechniquewithaindentationdepthabout1/10thofthelmthicknesstominimizethesubstratecontribution.
Sixreplicateindentationsweremadeforeachsample.
Thetribologicalbehaviorsofthelmswasmeasuredusingaball-on-platetribometer(CenterforTribologyUMT-3)atroomtemperaturewiththehumidityof50%underdryslidingcondition.
Asteelball(GCr15,HRC60)withadiameterat6mmwasusedasthefrictioncounterbody.
Allthetestswereperformedat20mm/sslidingvelocityforaslidingtimeof1200sandtheappliedloadwas3N.
Thelengthoftheweartrackwas5mmandthereciprocatingfrequencywas2Hz.
Aftertests,Fig.
1.
Al,Cr,CandOcontentsofAl:Cr-DLClmsasafunctionoftheC2H2fractioninthegasmixture.
theweartrackprolesweremeasuredbythesurfaceprolometer.
Andthewearrateswereevaluatedasvolumeperslidingdistanceperload.
3.
ResultsanddiscussionTheevolutionoftheAl,Cr,CandOcontentsintheAl:Cr-DLClmsispresentedinFig.
1asafunctionoftheC2H2fraction.
ItcanbeseenthatastheC2H2fractionincreased,boththeAlandCrcontentsdecreasedcontinuouslyfrom31.
8at.
%to8.
9at.
%andfrom17.
2at.
%to4.
7at.
%,respectively,whiletheCcontentincreasedfrom44.
7at.
%to83.
7at.
%,indicatingthatwecancontrolthedopedAlandCrcontentsofthelmsviaadjustingtheC2H2fractioningasmixture.
TheratiosofCrandArinthelmswerekeptataround0.
54,higherthanthatinthetarget(Cr/Al=30/70at.
%)weused.
ThisphenomenonmightbeduetothehighersputteringrateofCrthanthatofAl.
Asmallamountofoxygen(nothigherthan5at.
%)wasfoundinthelms.
Theexistenceofoxygencanbemainlyattributedtotheresidualoxygeninthechamberduetotherelativelyhighbasepressure.
HighresolutionXPSspectrafortheAl2p,Cr2p,andC1sregionsofthelmsareplottedinFig.
2(a)–(c),respectively.
ItcanbeseenthattheintensitiesoftheAl2pandCr2ppeaksincreasedwithdecreasingC2H2fraction,indicatingthattheAlandCrcontentsincreased.
TheAl2pspectracouldbedeconvolutedintotwopeaks:amajorpeakaround73eVandaweakpeakaround75eV,correspondingtoAlinthemetallicstateandAlinoxidestate,respectively.
Thisresultindicatesthataluminumdidnotbondwithcarbontoformcar-bide,whichcanalsobeillustratedbytheC1sspectra.
Normally,aluminumcarbidehasabindingenergyat281.
5eVandaluminumoxycarbidehasabindingenergyat282.
5eV[13,14].
However,bothofthemwerenotobservedintheC1sspectraofthelms,asshowninFig.
2(c).
TheCr2pspectrarevealasymmetricalsharppeakcen-teredat574eV,asexpectedforthe2p3/2stateofthemetallicCr.
Asmallpeakat575eVdeconvolutedfromthemajorpeakcouldbeassignedtoCrObonds.
However,thereisnosignicantdif-ferencebetweentheCr2ppeaksinthoseAl:Cr-DLClms.
PerviouspaperindicatedthattheCr2ppeakcouldnotbeusedeffectivelytodifferentiatethechemicalbondsbetweenmetallicCrandCrcar-bide[7].
Nevertheless,theC1sspectrumcanbeusetodeterminetheexistenceofthecarbide.
TheC1sspectraofthelmscouldbettedwiththreepeaks.
Thepeakattherelativelylowerbindingenergyofabout283eVcouldbeassignedtoCrCbondingandthePleasecitethisarticleinpressas:W.
Dai,etal.
,Microstructureandpropertyofdiamond-likecarbonlmswithAlandCrco-dopingdepositedusingahybridbeamssystem,Appl.
Surf.
Sci.
(2015),http://dx.
doi.
org/10.
1016/j.
apsusc.
2015.
11.
025ARTICLEINPRESSGModelAPSUSC-31742;No.
ofPages7W.
Daietal.
/AppliedSurfaceSciencexxx(2015)xxx–xxx3Fig.
2.
HighresolutionXPSspectrafor(a)Al2p;(b)Cr2p;and(c)C1sregionsforthelms;(d)thebondingfractionsoftheCrC,CC/CHandCObondsinlmsweredeterminedbytherelativepeakareasofthettedpeaksoftheC1sspectrainFig.
2(c).
peakaround285eVwasexpectedtooriginatefromthetypicalCCorCHbondinginDLClms.
Aweakpeakappearsatthebindingenergyofabout286eVcorrespondingtoCObonds.
ItshouldbenotedthatashiftofthemajorpeakoftheC1sspectrafromthecarbidebondingenergytohigherCCorCHbondingenergywasobserved,astheC2H2fractionincreasedfrom40%to70%,imply-ingthatthelmstructuretransformedfromacarbidefeaturetoaamorphouscarbonfeature.
ThebondfractionsoftheCrC(carbidephase),CC/CH(DLCphase)andCObondsinlmsweredeterminedbytherelativepeakareasofthettedpeaksoftheC1sspectraandarepresentedinFig.
2(d).
TheCObondinthelmshadremainedfairlycon-stantwithavaluelowerthan1%sincetheresidualOfavoredtobondwithAlandCrratherthanC.
Initially,thecarbidebondfrac-tionwasabout53.
8%,higherthantheCC/CHbondfractionofabout44%.
ThismeansthatthelmdepositedattheC2H2frac-tionof30%wasdominantlyconsistedofcarbidephase.
AstheC2H2fractionincreased,thecarbidebondfractiondecreasedcon-tinuouslywhiletheCC/CHfractionchangedintheoppositetrendsimultaneously.
WhentheC2H2fractionreachedto70%,thecarbidebondfractiondecreasedto1.
4%andtheCC/CHbondfractionincreasedto93.
8%,indicatingthatthelmwasdominantlyconsistedofDLCphase.
ManypapersreportedthatthecarbidestructurescouldbeformedjustasthecontentofthedopedmetalatomexceededitssolidsolubilitylimitintheDLCmatrix,whichwassignicantlycor-relatedwiththenatureofthedopedmetalaswellasthedepositiontechnique[7,15–17].
ItisnoteworthythatCrCwasstillfoundintheas-depositedlmswhentheCrcontentwasaslowas4.
7at.
%,whichmeansthattheCratomsinthelmshadasolidsolubilitylimitof50%,whichismuchhigherthanthepureDLClmsofabout39%[28].
TheimprovementoftheelasticresilienceofthelmsmightbemainlyattributedtotheformationoftheductileAl-richmultilayeredstructuresinthecarbonmatrixasshownintheTEMimage.
TheseductilemetalstructureshavebeexpectedtoovercomethebrittlenessandimprovethetoughnessoftheDLClms[11,29].
ThehighH/EratioandelasticrecoveryRareveryconducivetotribologicalpropertiesofthelms[30].
ThetribologicaltestsofthedepositedAl:Cr-DLClmswereper-formedontheball-on-platetribometer.
ThefrictioncoefcientofthelmsasafunctionofslidingdurationwasshowninFig.
7(a),andtheaveragefrictioncoefcientsandwearrateregardingtotheC2H2fractionwerepresentedinFig.
7(b).
ItcanbeseenthatthelmsdepositedattheC2H2fractionof70%exhibitedarela-tivelysteadyandlowfrictioncoefcientlowerthan0.
12,andaverysmallwearratesofabout1.
7*1015mm3N1m1.
AstheC2H2fractiondecreased,thefrictioncoefcientandwearrateofthelmsincreased.
SpeciallyfortheC2H2fractionof40%,althoughthelmhasthehighesthardnessatthispoint,thefrictioncoef-cientandwearratareachedtothehighestvaluesofabout0.
25and2.
1*1013mm3N1m1,respectively.
AtarelativelyhightheC2H2fraction(i.
e.
70%),thelmspossessahighH/Eratioandelas-ticrecoveryR,whicharebelievedtoeffectivelyreducethecontactpressureofthefrictionpairsviadistributingtheappliedloadoveralargerarea[31].
Asaresult,thelmsdisplayedexcellenttri-bologicalpropertieswithalowfrictioncoefcientandwearrate.
Pleasecitethisarticleinpressas:W.
Dai,etal.
,Microstructureandpropertyofdiamond-likecarbonlmswithAlandCrco-dopingdepositedusingahybridbeamssystem,Appl.
Surf.
Sci.
(2015),http://dx.
doi.
org/10.
1016/j.
apsusc.
2015.
11.
025ARTICLEINPRESSGModelAPSUSC-31742;No.
ofPages76W.
Daietal.
/AppliedSurfaceSciencexxx(2015)xxx–xxxFig.
5.
ResidualstressoftheAl:Cr-DLClmsasafunctionoftheC2H2fraction.
Fig.
6.
(a)HardnessandelasticmodulusofthelmsasafunctionoftheC2H2fraction;and(b)thehardness-modulusratiosandelasticrecoveryRofthelmsdepositedatdifferentC2H2fractions.
TheRwasdenedastheratioofthepartoftheindentationdepththatcanberecoverytothemaximumindentationdepthinnano-indentationload-displacementcurves.
However,astheC2H2fractiondecreased,theH/EratioandelasticrecoveryRofthelmsdecreased,whichcausedthecontactpres-sureandweartoincrease.
Inaddition,asthedopedCrcontentsincreased,alargeamountofhardcarbidephasewasformedintheDLCmatrixandthelmwasgraduallytransformedintoaFig.
7.
(a)Thefrictioncoefcientofthelmsasafunctionofslidingduration;and(b)theaveragefrictioncoefcientsandwearrateregardingtotheC2H2fraction.
carbide-richlm.
Thiswouldcauseabrasivewearandthusdeterio-ratethewearperformance,asveriedbytheobtainedhighfrictioncoefcientandwearrate.
4.
ConclusionsAl:Cr-DLClmsweredepositedusingthehybridionbeamsys-temcompositedoftheLISandtheHIPIMSwiththeAlCrtarget(Al/Cr=70/30at.
%).
ThedopedAlandCrcontentsinthelmsrangedfrom8.
9at.
%to31.
8at.
%andfrom4.
7at.
%to17.
2at.
%,respectively,viaadjustingtheC2H2fractionfrom70%to40%ingasmixtureofC2H2andAr.
ThecarbideformerCrdopedintoDLCmatrixpre-ferredtobondwithCtoformcarbidecomponentswhichcouldbeconducivetoimprovingthehardnessofthelms,whiletheweakcarbideformerAlexistedinmetallicstateandpresentedasAl-richmultilayeredstructure.
TheresidualstressofthelmscanbesignicantlyreleasedbytheformationoftheseAl-richlayers.
Inaddition,theAl-richlayerwasexpectedtoimprovethelmelas-ticrecoverywhichwereproposedasakeyparameterinwear.
Asaresult,thelmwiththemaximumelasticrecoverydepositedatC2H2fractionof70%exhibitedanexcellenttribologicalper-formancewithverylowfrictioncoefcient(0.
12)andwearrate(1.
7*1015mm3N1m1).
However,theformationofthehardcarbideintheDLCmatrixwouldcauseabrasivewearandthusdete-rioratethewearperformance,resultinginhighfrictioncoefcientandwearrate.
Pleasecitethisarticleinpressas:W.
Dai,etal.
,Microstructureandpropertyofdiamond-likecarbonlmswithAlandCrco-dopingdepositedusingahybridbeamssystem,Appl.
Surf.
Sci.
(2015),http://dx.
doi.
org/10.
1016/j.
apsusc.
2015.
11.
025ARTICLEINPRESSGModelAPSUSC-31742;No.
ofPages7W.
Daietal.
/AppliedSurfaceSciencexxx(2015)xxx–xxx7AcknowledgmentsThisworkwasnanciallysupportedinpartbytheprojectsoftheNationalNaturalScienceFoundationofChina(GrantNo:51405088)andtheNationalNaturalScienceFoundationofGuang-dongprovince(GrantNo:2014A030313516).
ItwasalsosupportedinpartbyagrantfromtheZhujiangNewStarofScienceandTech-nologyofGuangzhouCity(GrantNo:201506010091).
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