外文翻译激光焊AGPDAUCU合金显微结构和腐蚀状态的研究在牙科领域的应用英文版精品.docx

外文翻译激光焊AGPDAUCU合金显微结构和腐蚀状态的研究在牙科领域的应用英文版精品.docx

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外文翻译激光焊AGPDAUCU合金显微结构和腐蚀状态的研究在牙科领域的应用英文版精品

Laserweld:

microstructureandcorrosionstudyofAg–Pd–Au–Cualloyofthedentalapplication

M.L.Santos*,H.A.Acciari,L.C.O.Vercik,A.C.GuastaldiInstitutodeQuı´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,thespectrumiscontrolledbythe

occurrenceofastraightline,andanewRpandCPEpcompositionwasusedtorepresenttheformationofapermeablenatureinterfacesincethisdispersion,observedduringthefrequencyvariation,mayhavebeenoriginatedfromtheformationofpitsonthesurface,thusconfirmedbytheopticmicroscopyanalysisafterthecorrosionessays（notshowed）andbythesignificantdecreaseonthepolarizationresistancenumberfromaround10kVcm2to100Vcm2（Table2）.Accordingtothe

correspondentimpedancediagramsobtainedwiththeBodeformat,fairconcordancebetweentheexperimentalandcalculatednumbersisobserved.

TheuseofoneCPEtosubstitutethedoubleelectricallayerisduetoacorrectionofthedistortionscausedbytheuniformityinthecurrent

distributioncausedbythegeometryoftheelectrodicsurface[11–13].Adiffusionprocessrepresented

byastraightlineonthecomplexplaneandbythedistortiondegree,ac0.5（Table2）,isobs