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英语文献Word文件下载.docx
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Laserweld:
micadeAraraquara-UNESP,C.P.355,14800-900Araraquara,Sa˜oPaulo,BrazilReceived10June2002;
accepted20June2002
Abstract
Thelaserweldingprocesswasintroducedintodentistrybytheendofthe1980s,resultingonagreatimpulsetothatareawiththedevelopmentofcheaperandsmallerequipment,usingsimplertechnique.Thisallowedgreateruseofthatprocessontheconfectionofprosthesescomparedtothebrazingprocesssincetheheatsourceforthatprocessisaconcentratedlightbeamofhighpower,whichminimizesdistortionproblemsontheprostheticpieces.Ag–Pd–Au–Cualloyusedontheconfectionofdentalimplantprostheseswasobservedbeforeandaftersubjectiontothelaserweldingprocess.
Themicrostructurewasanalyzedwiththeuseofopticmicroscopyandthecorrosionresistancewasstudiedbythetraditionalelectrochemicaltechniquesandbyelectrochemicalimpedance,underenvironmentalconditionssimulatingtheaggressivenessfoundinthemouthcavity.Astructuralchangewasdetectedontheweldarea,whichpresentedarefinedmicrostructurederivingfromthehigh-speedcooling.
Thebasemetaloutoftheweldareapresentedafusioncoarsemicrostructure.Theelectrochemicalessaysshoweddifferencesonthepotentiodynamicpolarizationbehaviorinbothweldandmetalbaseareas,indicatingsuperiorcorrosionresistanceinthe
weldarea.Theimpedancespectrawerecharacterizedbycapacitivedistortedcomponents,presentinglinearimpedanceinthelowfrequenciesarea.D2002ElsevierScienceB.V.Allrightsreserved.
Keywords:
Ag–Pd–Au–Cu;
Laser;
Corrosion;
Dentalalloys
1.Introduction
Insearchforalternativemetalalloysforodontologicalpurposes,someresearchershaveappliedtheAgPdalloytosubstitutethegoldalloys,tryingtoreducecostsandtoimprovemechanicalpropertiesandcorrosionresistance[1–4].Duetosomedifficultyinobtainingadaptationinprostheticpieces,mainlythelargeronessuchasmetallicstructuresmoltenintoonepiece,calledcastmonoblocks,theuseofweldingisnecessarysincethistechniqueacceptstheworkwithsegmentsoftheprosthesis,whichmakespossibleabalancedforcedistributionandthebestsuitableadaptation,occurringinanaccuratepassiveway
[4,5].
Theprocessoflaserweldingproducesacoherent,monochromatic,concentratedlightbeamofhighpower,andithasbeenappliedtosubstitutethebrazinginodontologicalprostheseswelding.Thelaserweldingprocesswasintroducedintodentistrybytheendofthe1980s,resultingonagreatimpulsetotheareawiththedevelopmentofcheaperandsmallerequipmentduetoitsadvantagesandwideapplication,whichmadepossibletouseweldinginawidevarietyofmetalsandprostheticpieces[6].
Theuseofelectrochemicaltechniquesinthecorrosionstudyisimportantfortheunderstandingofitsperformance,biocompatibilityandbiofunctionality,whenclinicallyapplied,fortheseareconstantlyexposedtoaggressiveenvironments.
ThisresearchobservesAg–Pd–Au–Cualloymicrostructurebehaviorandthematerial’sresistancetocorrosionunderenvironmentalconditionssimulatingtheaggressivenessfoundinthemouthcavity,whenusedondentalimplantprosthesesbeforeandafter
subjectedtothelaserweldingprocess.
2.Experimental
Table1presentsthemineralcompositionofthestudiedmaterial,usingWaveDispersiveSpectroscopy—WDS.Thecylindricaltestspecimens,with0.27-cmdiameterand1.0-cmlength,havebeensubjectedtotheweldingprocessonbuttjoints[7].Theweldingmachine,DentaurumDL20002S,usedforthelaserwelding,usesacrystalNdYAGassourceoflaser,andthebeampowerwasapproximately6.08kWin14ms,originatingaweldingenergyofapproximately85.12J.Thetestspecimensweremanuallyplacedinthechamber,withshieldatmosphereofargon,andspotsoflapwelding,inapproximately2/3ofthesurfaces,wereappliedinthewholesectionofthejoint,with60%ofbeampenetration.Aprecisediscmodel15HCDIAMONDwasusedtoobtainthetestspecimensofAg–Pd–Au–Cualloywithareacomprehendingonlytheweldingarea,andanISOMET1000-BUEHLERmachinewasusedtoseparatethebasemetalfromtheweldingareaafterthelaserprocess.Theexposedgeometric
areasoftheweldingcordandofthebasemetalwere0.057cm2.Themetallographicanalysisoftheexposedsurfaceofthebasemetalandtheweldingareawasdonewithopticmicroscopy,afterpolish
withemeryclothfrom180to1000mesh,aluminawithgranulation1and0.3Amandnitro-muriaticacidapplication[8].Theworkelectrodeswerepreparedfromthetestspecimensusedonthemetallographicanalysis.Measuresofopencircuitpotentialversus
timewereusedintheelectrochemicalessays,aswellaspotentiodynamicpolarizationandelectrochemicalimpedance.AnelectrochemicalcellcontainingNaCl0.15moll_1(0.9%)airysolutionwiththreeelectrodeswasalsoused,withthesaturatedcalomelelectrode(SCE)asreferencesystemandagraffiticylinderasauxiliaryelectrode.ElectrochemicalmeasuresofcorrosionweredonewithapotentiometerSolartronSI1287.Potentiodynamic
polarizationcurveswereobservedat0.001Vs_1immediately.Impedancemeasuresweredonewiththeanalyzeroffrequencyresponse,Solartron1255,connectedtoanelectrochemicalinterface,Solartron1287,andanamplitudeof10mVwasappliedtoafrequencychannelthatvariedfrom100kHzto6MHz,obtainingfivepointsforeachfrequencydecade,controlled
bythesoftwareZplot[9].ThesoftwareZveiw[10]wasresponsiblefortheadjustments
3.Resultsanddiscussion
Fig.1presentsacoarsebiphasicfusionmicrostructureinthebasemetalarea.
Fig.2illustratesarefineddendriticalmicrostructureinthelaserweldarea,derivingfromthehighspeedycoolingimposedbythelaserweldbecauseofalocatedfusionprocess,followedbyaquickcoolingduringthewelding,whichdoesnotallowthemicrostructuretoreturntoitsinitialbiphasicstructure.
Fig.3showstheopencircuitpotentialversustimecurvesforthebasemetalandlaserweldareasoftheAg–Pd–Au–Cualloy.Thestabilizationofthepotentialwasobserved3hafterimmersionforbothareas,andthelaserweldpresentedastabilizationpotential50mVhigher.SomeAgPdalloyresearchershaveobservedthat,usually,analloyopencircuitpotentialincreaseswiththeincreaseofthenoblemetalsconcentration[1].
showminutedetailstheobservation
Showminutedetailstheobservationtoincludetoscantogiveorgetanelectricshockthemirrorandgoldsgenerallymutuallyanalyticalwait.
Scanningtogiveorgetanelectricshockthemirroranalysisistowillbreaktheoraltestpiecetoplaceinscantogiveorgetanelectricshockthemirrorobservation
Itscrystalstructure,splitthecharacteristic,deep,pore,hotinfluenceareaSizeetc..ThegoldismutuallyanalyticaltotrythepiecetotheweldingtomakeintothegoldfirsttowhetmutuallySlice,throughthesoureclipse,clean,blowthestemtopostposeismutuallythemicroscopeinthegoldnext,Observeitsareaorganizationstructure,theisdeepandmeltstheareaandhotinfluenceareas
Sizeetc..Chaietc.theisinthegoldofthepieceofmutuallyanalyticallydetection,Connectthesetdisplaysthebrittlenessopenwoundshapeofsplitthe,butmatchedcontrolthenis.
Thetenacityopenwoundofthecupform,theconeformphenomenon.,thisisfromthetinyviewlastreflection
Thetenacityofthepieceoflower:
Discoverthelaserwhilestudythelaserwelding
Thehotinfluenceareagrainofthepieceofissmaller,appearingonlyonehorsesurnamebodystructure,
Butdealwithcontactfortheweldingofthe3mmsatthediameterallthenotyetfinishedwholeisdeeply
ThepolarizationcurvesonFig.4presentdifferencesontheanodicbehavior,withtheoccurrenceofanareacorrespondingtothefirsttranspassiveregion
closeto+0.07V(SCE)onthelaserweld.Thenumbersobtainedforthecorrosionpotentials,Ecor,indicatethatthelaserweldareapresentshigher
corrosionresistance.Theimpedanceresponsesoriginatedintheopen
circuitpotential,obtainedinthesteadystateforthebasemetalarea,presenttheoccurrenceofonedistortedsemicircleathighfrequencies(Fig.5).
TheequivalentelectricalcircuitmodelbetteradjustabletothecharacteristicsoftheresultingspectrumiscomposedofaparallelassociationofRTCand
CPE,whichrepresentstheelectrochemicalbehavioroftheinterfaceinthehighfrequenciesarea,include-includingonlyonechargetransferprocess.Inthelowfrequenciesareas,thespectrumiscontrolledbyth
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