外文翻译--激光焊：Ag-Pd-Au-Cu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.doc

Laserweld:microstructureandcorrosionstudyofAgPdAuCualloyofthedentalapplicationM.L.Santos*,H.A.Acciari,L.C.O.Vercik,A.C.GuastaldiInstitutodeQumicadeAraraquara-UNESP,C.P.355,14800-900Araraquara,SaoPaulo,BrazilReceived10June2002；accepted20June2002AbstractThelaserweldingprocesswasintroducedintodentistrybytheendofthe1980s,resultingonagreatimpulsetothatareawiththedevelopmentofcheaperandsmallerequipment,usingsimplertechnique.Thisallowedgreateruseofthatprocessontheconfectionofprosthesescomparedtothebrazingprocesssincetheheatsourceforthatprocessisaconcentratedlightbeamofhighpower,whichminimizesdistortionproblemsontheprostheticpieces.AgPdAuCualloyusedontheconfectionofdentalimplantprostheseswasobservedbeforeandaftersubjectiontothelaserweldingprocess.Themicrostructurewasanalyzedwiththeuseofopticmicroscopyandthecorrosionresistancewasstudiedbythetraditionalelectrochemicaltechniquesandbyelectrochemicalimpedance,underenvironmentalconditionssimulatingtheaggressivenessfoundinthemouthcavity.Astructuralchangewasdetectedontheweldarea,whichpresentedarefinedmicrostructurederivingfromthehigh-speedcooling.Thebasemetaloutoftheweldareapresentedafusioncoarsemicrostructure.Theelectrochemicalessaysshoweddifferencesonthepotentiodynamicpolarizationbehaviorinbothweldandmetalbaseareas,indicatingsuperiorcorrosionresistanceintheweldarea.Theimpedancespectrawerecharacterizedbycapacitivedistortedcomponents,presentinglinearimpedanceinthelowfrequenciesarea.D2002ElsevierScienceB.V.Allrightsreserved.Keywords:AgPdAuCu；Laser；Corrosion；Dentalalloys1.IntroductionInsearchforalternativemetalalloysforodontologicalpurposes,someresearchershaveappliedtheAgPdalloytosubstitutethegoldalloys,tryingtoreducecostsandtoimprovemechanicalpropertiesandcorrosionresistance14.Duetosomedifficultyinobtainingadaptationinprostheticpieces,mainlythelargeronessuchasmetallicstructuresmoltenintoonepiece,calledcastmonoblocks,theuseofweldingisnecessarysincethistechniqueacceptstheworkwithsegmentsoftheprosthesis,whichmakespossibleabalancedforcedistributionandthebestsuitableadaptation,occurringinanaccuratepassiveway4,5.Theprocessoflaserweldingproducesacoherent,monochromatic,concentratedlightbeamofhighpower,andithasbeenappliedtosubstitutethebrazinginodontologicalprostheseswelding.Thelaserweldingprocesswasintroducedintodentistrybytheendofthe1980s,resultingonagreatimpulsetotheareawiththedevelopmentofcheaperandsmallerequipmentduetoitsadvantagesandwideapplication,whichmadepossibletouseweldinginawidevarietyofmetalsandprostheticpieces6.Theuseofelectrochemicaltechniquesinthecorrosionstudyisimportantfortheunderstandingofitsperformance,biocompatibilityandbiofunctionality,whenclinicallyapplied,fortheseareconstantlyexposedtoaggressiveenvironments.ThisresearchobservesAgPdAuCualloymicrostructurebehaviorandthematerialsresistancetocorrosionunderenvironmentalconditionssimulatingtheaggressivenessfoundinthemouthcavity,whenusedondentalimplantprosthesesbeforeandaftersubjectedtothelaserweldingprocess.2.ExperimentalTable1presentsthemineralcompositionofthestudiedmaterial,usingWaveDispersiveSpectroscopyWDS.Thecylindricaltestspecimens,with0.27-cmdiameterand1.0-cmlength,havebeensubjectedtotheweldingprocessonbuttjoints7.Theweldingmachine,DentaurumDL20002S,usedforthelaserwelding,usesacrystalNdYAGassourceoflaser,andthebeampowerwasapproximately6.08kWin14ms,originatingaweldingenergyofapproximately85.12J.Thetestspecimensweremanuallyplacedinthechamber,withshieldatmosphereofargon,andspotsoflapwelding,inapproximately2/3ofthesurfaces,wereappliedinthewholesectionofthejoint,with60%ofbeampenetration.Aprecisediscmodel15HCDIAMONDwasusedtoobtainthetestspecimensofAgPdAuCualloywithareacomprehendingonlytheweldingarea,andanISOMET1000-BUEHLERmachinewasusedtoseparatethebasemetalfromtheweldingareaafterthelaserprocess.Theexposedgeometricareasoftheweldingcordandofthebasemetalwere0.057cm2.Themetallographicanalysisoftheexposedsurfaceofthebasemetalandtheweldingareawasdonewithopticmicroscopy,afterpolishwithemeryclothfrom180to1000mesh,aluminawithgranulation1and0.3Amandnitro-muriaticacidapplication8.Theworkelectrodeswerepreparedfromthetestspecimensusedonthemetallographicanalysis.Measuresofopencircuitpotentialversustimewereusedintheelectrochemicalessays,aswellaspotentiodynamicpolarizationandelectrochemicalimpedance.AnelectrochemicalcellcontainingNaCl0.15moll_1(0.9%)airysolutionwiththreeelectrodeswasalsoused,withthesaturatedcalomelelectrode(SCE)asreferencesystemandagraffiticylinderasauxiliaryelectrode.ElectrochemicalmeasuresofcorrosionweredonewithapotentiometerSolartronSI1287.Potentiodynamicpolarizationcurveswereobservedat0.001Vs_1immediately.Impedancemeasuresweredonewiththeanalyzeroffrequencyresponse,Solartron1255,connectedtoanelectrochemicalinterface,Solartron1287,andanamplitudeof10mVwasappliedtoafrequencychannelthatvariedfrom100kHzto6MHz,obtainingfivepointsforeachfrequencydecade,controlledbythesoftwareZplot9.ThesoftwareZveiw10wasresponsiblefortheadjustments3.ResultsanddiscussionFig.1presentsacoarsebiphasicfusionmicrostructureinthebasemetalarea.Fig.2illustratesarefineddendriticalmicrostructureinthelaserweldarea,derivingfromthehighspeedycoolingimposedbythelaserweldbecauseofalocatedfusionprocess,followedbyaquickcoolingduringthewelding,whichdoesnotallowthemicrostructuretoreturntoitsinitialbiphasicstructure.Fig.3showstheopencircuitpo