1、Laserweld/microstructureandcorrosionstudyofAgPdAuCualloyofthedentalapplicationM/L/Santos*/H/A/Acciari/L/C/O/Vercik/A/C/GuastaldiInstitutodeQumicadeAraraquara-UNESP/C/P/355/14800-900Araraquara/SaoPaulo/BrazilReceived10June2002；accepted20June2002AbstractThelaserweldingprocesswasintroducedintodentistry
2、bytheendofthe1980s/resultingonagreatimpulsetothatareawiththedevelopmentofcheaperandsmallerequipment/usingsimplertechnique/Thisallowedgreateruseofthatprocessontheconfectionofprosthesescomparedtothebrazingprocesssincetheheatsourceforthatprocessisaconcentratedlightbeamofhighpower/whichminimizesdistorti
3、onproblemsontheprostheticpieces/AgPdAuCualloyusedontheconfectionofdentalimplantprostheseswasobservedbeforeandaftersubjectiontothelaserweldingprocess/Themicrostructurewasanalyzedwiththeuseofopticmicroscopyandthecorrosionresistancewasstudiedbythetraditionalelectrochemicaltechniquesandbyelectrochemical
4、impedance/underenvironmentalconditionssimulatingtheaggressivenessfoundinthemouthcavity/Astructuralchangewasdetectedontheweldarea/whichpresentedarefinedmicrostructurederivingfromthehigh-speedcooling/Thebasemetaloutoftheweldareapresentedafusioncoarsemicrostructure/Theelectrochemicalessaysshoweddiffere
5、ncesonthepotentiodynamicpolarizationbehaviorinbothweldandmetalbaseareas/indicatingsuperiorcorrosionresistanceintheweldarea/Theimpedancespectrawerecharacterizedbycapacitivedistortedcomponents/presentinglinearimpedanceinthelowfrequenciesarea/D2002ElsevierScienceB/V/Allrightsreserved/Keywords/AgPdAuCu；
6、Laser；Corrosion；Dentalalloys1/IntroductionInsearchforalternativemetalalloysforodontologicalpurposes/someresearchershaveappliedtheAgPdalloytosubstitutethegoldalloys/tryingtoreducecostsandtoimprovemechanicalpropertiesandcorrosionresistance14/Duetosomedifficultyinobtainingadaptationinprostheticpieces/m
7、ainlythelargeronessuchasmetallicstructuresmoltenintoonepiece/calledcastmonoblocks/theuseofweldingisnecessarysincethistechniqueacceptstheworkwithsegmentsoftheprosthesis/whichmakespossibleabalancedforcedistributionandthebestsuitableadaptation/occurringinanaccuratepassiveway4/5/Theprocessoflaserwelding
8、producesacoherent/monochromatic/concentratedlightbeamofhighpower/andithasbeenappliedtosubstitutethebrazinginodontologicalprostheseswelding/Thelaserweldingprocesswasintroducedintodentistrybytheendofthe1980s/resultingonagreatimpulsetotheareawiththedevelopmentofcheaperandsmallerequipmentduetoitsadvanta
9、gesandwideapplication/whichmadepossibletouseweldinginawidevarietyofmetalsandprostheticpieces6/Theuseofelectrochemicaltechniquesinthecorrosionstudyisimportantfortheunderstandingofitsperformance/biocompatibilityandbiofunctionality/whenclinicallyapplied/fortheseareconstantlyexposedtoaggressiveenvironme
10、nts/ThisresearchobservesAgPdAuCualloymicrostructurebehaviorandthematerialsresistancetocorrosionunderenvironmentalconditionssimulatingtheaggressivenessfoundinthemouthcavity/whenusedondentalimplantprosthesesbeforeandaftersubjectedtothelaserweldingprocess/2/ExperimentalTable1presentsthemineralcompositi
11、onofthestudiedmaterial/usingWaveDispersiveSpectroscopyWDS/Thecylindricaltestspecimens/with0/27-cmdiameterand1/0-cmlength/havebeensubjectedtotheweldingprocessonbuttjoints7/Theweldingmachine/DentaurumDL20002S/usedforthelaserwelding/usesacrystalNdYAGassourceoflaser/andthebeampowerwasapproximately6/08kW
12、in14ms/originatingaweldingenergyofapproximately85/12J/Thetestspecimensweremanuallyplacedinthechamber/withshieldatmosphereofargon/andspotsoflapwelding/inapproximately2/3ofthesurfaces/wereappliedinthewholesectionofthejoint/with60%ofbeampenetration/Aprecisediscmodel15HCDIAMONDwasusedtoobtainthetestspec
13、imensofAgPdAuCualloywithareacomprehendingonlytheweldingarea/andanISOMET1000-BUEHLERmachinewasusedtoseparatethebasemetalfromtheweldingareaafterthelaserprocess/Theexposedgeometricareasoftheweldingcordandofthebasemetalwere0/057cm2/Themetallographicanalysisoftheexposedsurfaceofthebasemetalandtheweldinga
14、reawasdonewithopticmicroscopy/afterpolishwithemeryclothfrom180to1000mesh/aluminawithgranulation1and0/3Amandnitro-muriaticacidapplication8/Theworkelectrodeswerepreparedfromthetestspecimensusedonthemetallographicanalysis/Measuresofopencircuitpotentialversustimewereusedintheelectrochemicalessays/aswell
15、aspotentiodynamicpolarizationandelectrochemicalimpedance/AnelectrochemicalcellcontainingNaCl0/15moll_1(0/9%)airysolutionwiththreeelectrodeswasalsoused/withthesaturatedcalomelelectrode(SCE)asreferencesystemandagraffiticylinderasauxiliaryelectrode/Electrochemicalmeasuresofcorrosionweredonewithapotenti
16、ometerSolartronSI1287/Potentiodynamicpolarizationcurveswereobservedat0/001Vs_1immediately/Impedancemeasuresweredonewiththeanalyzeroffrequencyresponse/Solartron1255/connectedtoanelectrochemicalinterface/Solartron1287/andanamplitudeof10mVwasappliedtoafrequencychannelthatvariedfrom100kHzto6MHz/obtainin
17、gfivepointsforeachfrequencydecade/controlledbythesoftwareZplot9/ThesoftwareZveiw10wasresponsiblefortheadjustments3/ResultsanddiscussionFig/1presentsacoarsebiphasicfusionmicrostructureinthebasemetalarea/Fig/2illustratesarefineddendriticalmicrostructureinthelaserweldarea/derivingfromthehighspeedycooli
18、ngimposedbythelaserweldbecauseofalocatedfusionprocess/followedbyaquickcoolingduringthewelding/whichdoesnotallowthemicrostructuretoreturntoitsinitialbiphasicstructure/Fig/3showstheopencircuitpotentialversustimecurvesforthebasemetalandlaserweldareasoftheAgPdAuCualloy/Thestabilizationofthepotentialwasobserved3hafterimmersionforbothareas/andthelaserweldpresentedastabilizationpotential50mVhigher/SomeAgPdalloyresearchershaveobservedthat/usually/analloyopencircuitpotential
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