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外文翻译--基于温激光喷丸中动态应变时效和动态析出的AISI4140钢疲劳行为的改进 英文版.pdf

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外文翻译--基于温激光喷丸中动态应变时效和动态析出的AISI4140钢疲劳行为的改进 英文版.pdf

KimUniversitogy8WarmlasershockpeeningWLSPisathermomechanicaltreatmenttechniquecombiningtheadvantagesoflasershockpeeninganddynamicstrainagingDSA.ThroughDSA,WLSPofsteelincreasesthedislocationdensityandstabilizesthedislocationstructurebypeeningLSPhasbeensuccessfullyusedtoimprovetheafterLSPanddeeprollingDR.Hu5investigatedLSPofAISI1045steelbyANSYS,validatedbyexperiment.Chu6comparedthemicrostructure,hardnessandresidformationofahighdensityemartensitephase.effectoffatiguelifeimprovementbyLSPislimited.Thus,itisveryimportanttostabilizethemicrostructureandthecompressiveresidualstressgeneratedbyLSP.DynamicstrainagingDSAandDPcanbothimprovethemicrostructurestabilityofmetallicmaterials.DSA12,13,thediffusionofCcarbonandNnitrogenatoms⇑Correspondingauthor.Emailaddressgjchengpurdue.eduG.J.Cheng.Availableonlineatwww.sciencedirect.comActaMaterialia5920111014–1025fatigueperformanceofmetalliccomponents1.Bygeneratingaworkhardenedlayerandintroducingcompressiveresidualstressinthematerialsurfacethespeedofcrackinitiationandpropagationduringcyclicloadingissloweddown,whichresultsinafatigueperformanceimprovement.LSPisaneffectivewaytoimprovesurfacehardness,fatigueperformance,corrosionresistanceandwearresistance2.Steelsarewidelyusedinindustry.LSPofsteelhasbeenextensivelystudiedintheliterature.Forexample,Nikitin3,4comparedthenearsurfacemicrostructurechangeandfatiguelifeimprovementofAISI304stainlesssteelHowever,thecompressiveresidualstressgeneratedbysurfaceprocessingtechniquesSP,LSP,DP,etc.isnotstableduringcyclicloading7,8,especiallyathightestingtemperatures3,4,9,10.Forexample,Altenbergeretal.11investigatedthethermalstabilityofthecompressiveresidualstressandsurfacenanostructuregeneratedinAISI304stainlesssteelandTi64alloybydynamicprecipitationDPandLSPbyinsitutransmissionelectronmicroscopyTEMstudy.Itwasobservedthatcompleteresidualstressrelaxationat550–600C176Cwasrelatedtothethermalinstabilityofthenearsurfacemicrostructure.Inthisway,thepinningofmobiledislocationsbycarbonatoms.Inaddition,WLSPgeneratesnanoscalecarbideprecipitatesthroughstraininducedprecipitation.Thecarbideprecipitatesstabilizethemicrostructurebydislocationpinning.Thisresultsinhigherstabilityofthedislocationstructureandthusimprovesthestabilityofthecompressiveresidualstress.InthisstudythemechanismoffatigueperformanceimprovementinAISI4140steelbyWLSPisinvestigated.ItisfoundthatmicrostructuresformedafterWLSPleadtoahigherstabilityofdislocationstructuresandresidualstress,whicharebeneficialforfatigueperformance.C2112010ActaMaterialiaInc.PublishedbyElsevierLtd.Allrightsreserved.KeywordsWarmlasershockpeeningAISI4140steelDynamicstrainagingDynamicprecipitationCarbide1.IntroductionAsasuperiorsurfaceprocessingtechnique,lasershockualstressgeneratedbyLSP,DRandshotpeeningSPonHadfieldmanganesesteel.InChusstudyitwasfoundthatLSPresultedinalargehardnessincreaseduetotheFatigueperformanceimprovementstrainaginganddynamicprecipitationChangYea,SergeySuslovb,BongJoongaSchoolofIndustrialEngineering,PurduebSchoolofMaterialsEngineeringandBirckNanotechnolReceived30July2010receivedinrevisedformAvailableonlineAbstract13596454/36.00C2112010ActaMaterialiaInc.PublishedbyElsevierLtd.Alldoi10.1016/j.actamat.2010.10.032inAISI4140steelbydynamicduringwarmlasershockpeeningb,EricA.Stachb,GaryJ.Chenga,⇑y,WestLafayette,IN47906,USACenter,PurdueUniversity,WestLafayette,IN,USA13October2010accepted13October2010November2010www.elsevier.com/locate/actamatrightsreserved.todislocationcoresinthetemperaturerange150–300C176C,isanimportantstrengtheningmechanism14insteel.InDSAtheinteractionbetweendislocationsandsoluteatomsresultsinrepeatedpinningofdislocationsandthusleadstoenhancedworkhardening13,15.AttheDSAtemperaturethesoluteatomscarbonandnitrogenmigratetodislocationcores,whichformsocalledCottrellclouds16insteel.TheCottrellcloudsexertapinningforceondislocationsandinhibitdislocationmovementduringplasticdeformation.Forplasticdeformationtocontinue,newmobiledislocationsmustbegenerated.Thisleadstodislocationmultiplicationandresultsinahigherdislocationdensityandamoreuniformdislocationarrangement.SubstantialeffortshavebeenmadetotakeadvantageofDSAintreatingsteel.Forexample,Chen17improvedthefatigueperformanceofAISI304stainlesssteelbyplasticdeformationattheDSAtemperature.Kerscheretal.18increasedthefatiguelimitofSAE52100steelbyTMTattheDSAtemperature,andidentifiedtheoptimaltemperature335C176Cthatledtobestfatigueperformanceimprovement.Huangetal.19comparedthefatigueperformanceofSA533B3steelatroomtemperatureand300C176Candfoundthatthebetterfatigueperformanceat300C176CwasacombinedeffectofDSAandtheformationofcarbideprecipitatesduringcyclicloading.DynamicprecipitationduringhotdeformationisalsoknownasstraininducedprecipitationSIP.Dynamicprecipitationdiffersfromstaticprecipitationinthattheformerresultsintheformationofnanoscaleprecipitatesdynamicallyduringwarmdeformation.Indynamicprecipitationthedislocationsgeneratedbydeformationactasfavorablenucleationsitestogrowprecipitatesdynamically.Comparedwithstaticprecipitation,dynamicprecipitationismoreefficientinstrengtheninginthatittakesamuchshortertimetoreachpeakhardness.Tiittoetal.20investigatedtheeffectofdynamicprecipitationinsteelonthehotflowbehaviorofalloysteel.Itwasfoundthatthepeakpinningforceresultingfromdynamicprecipitationleadstoapeakintheflowcurveduringhotdeformation.Asdiscussedearlier,DSAcanincreasethedislocationdensitygeneratedbydeformation.Thehighdensitydislocations,inturn,canprovidenumerouspotentialnucleationsitesfordynamicprecipitation.Thus,theeffectivenessofDPcanbeimprovedthroughDSA.Liaoetal.21proposedanucleationmechanismtoexplaintheultrahighdensenanoprecipitationduringWLSP,andfoundthatdislocationsafterhighstrainratedeformationandelevatedtemperaturesarethetwomostimportantfactors.Thenucleationmodelwasvalidatedbyexperiments.Theperformanceofsurfaceprocessingtechniques,includingLSP,DRandSP,canbeimprovedbytakingadvantageofDSAandDP.Matlock15comparedtheeffectofDRofAISI4140steelatroomtemperatureand260C176CDSAtemperature.ItwasfoundthatDRattheDSAtemperaturesignificantlyincreasedthecorehardnessC.Yeetal./ActaMaterialiaandalsoledtoamorestabledislocationstructureandthusimprovedthefatigueperformance.HightemperatureDRofaluminumalloyswasalsoproventobemoreeffectiveinfatigueperformanceimprovementthanroomtemperatureDRbyJuijerm22–24.Harada25comparedshotpeeningofspringsteelatroomtemperatureandelevatedtemperatures100C176C,200C176C,300C176Cand400C176C.ItwasfoundthatSPattheoptimaltreatmenttemperature200C176Ctendstoincreasethenearsurfacecompressiveresidualstressmagnitudeandhardnessduetothedecreaseinflowstressathightemperature.Inaddition,itwasfoundthatthemagnitudeoftheresidualstressgeneratedbySPdecreasedduetorecoveryattreatmenttemperatureshigherthan200C176C.ThoughitwasnotmentionedbyHarada,theincreaseinhardnessat200C176CintheDSAtemperatureregimecouldalsobepartiallyattributabletoDSA,whichledtothepinningofdislocationsbyCottrellcloudsandresultedinahigherdislocationdensityandgreaterworkhardening.InthewarmshotpeeningworkonAISI4140steelcarriedoutbyWick26andMenigandSchulze27itwasdemonstratedthatSPatelevatedtemperaturearound300C176Cimprovedtheresidualstressstabilityandledtobetterfatigueperformance.AccordingtoWick26,inthewarmpeeningsamplesstaticanddynamicstrainagingoccursimultaneouslyduringandafterwarmpeening,whichleadstoahighersurfacehardness.Inaddition,DSAinwarmshotpeeningleadstotheformationofahighdensityofdislocationsandmoreuniformdislocationarrangement,whichcontributetoahigherresidualstressstabilityduringcyclicloading.AsasuperiorsurfaceprocessingtechniqueLSPcanalsotakeadvantageofTMTbytreatingsteelintheDSAtemperatureregime150–300C176C.Thus,itisofinteresttoinvestigatetheeffectoftreatingtemperatureonthefatigueperformanceimprovementbyLSP.Inapreviousstudybyourgroup28itwasfoundthatwarmlasershockpeeningWLSPcansignificantlyimprovethestabilityofthecompressiveresidualstressinAA6061alloysthroughthepinningofdislocationsbytheformationofahighdensityofnanoscaleprecipitatesgeneratedbydynamicprecipitation.InthisworkWLSPofAISI4140steelwascarriedoutanditseffectsonfatigueperformancewerestudied.ThemicrostructureofthesamplestreatedafterLSPandWLSPwascharacterizedbytransmissionelectronmicroscopyTEM.TheresidualstressanddislocationdensityweremeasuredbyXraydiffraction.2.Experiments2.1.MaterialsSampleswerecutandmachinedfromaAISI4140steelplatewiththechemicalcomposition0.41C,0.21Si,0.83Mn,0.025P,0.027S,0.91Cr,0.18Mo,theremainderFeallwt..Thesampledimensionswere76.2C210C22.38mm.BeforeLSPthesampleswereaustenitizedfor20minat850C176C,oilquencheddownto25C176C,5920111014–10251015temperedat450C176Cfor2handcooledinavacuumfurnace.ThisprocedureresultsinsteelwithaVickershardnessof310VHandamicrostructureoftemperedmartensiteFig.4.2.2.WarmlasershockpeeningexperimentsAschematicoftheWLSPprocessisshowninFig.1.BK7glasswasusedastheconfiningmediumduetoitshighshockimpedanceandhighmeltingpoint,makingitsuitableforLSPatelevatedtemperatures.Inthiscasewatercannotbeusedastheconfiningmediumduetoitslowevaporationpoint.Inpractice,siliconeoiltype710couldalsobeusedforconfinement,duetoitshighvaporpointC24300C176Ccomparedwithwater.Thinaluminumfoilisusedasanablativecoatingmaterialtoprotectthetargetmaterialfromsurfacemelting.TheworkingtemperaturesforWLSParemanipulatedusingahotplate.Athermometerisusedtomonitorthesampletemperature.Thelaserbeamsizeusedis1mm.Theoverlapratiois75.FurtherdetailsoftheWLSPexperimentcanbefoundinYeetal.28.2.3.Characterization2.3.1.MicrohardnessThemicrohardnesschangeofthesamplesbeforeandafterLSPorWLSPismeasuredusingaLecoM400Hmicrohardnesstestmachinewitha200gloadanda10sFig.1.Schematicofthelasershockpeeningprocess.1016C.Yeetal./ActaMaterialiaholdingtime.Theaverageoffivemeasurementswasusedforeachdatapoint.2.3.2.ResidualstressABrukerD8DiscoverXraymicrodiffractionsystemwasusedtomeasuretheresidualstressofthesample.TheXraycollimatorusedinthisworkis0.1mmindiameter.The{220}peakwasusedforstressanalysis,whichcorrespondstoa2hangleof123.916C176intheunstressedstate.Theinterferencelinesofthesteelphaseweredeterminedat11wanglesfromC050C176to50C176usingCoKa1radiationandanalyzedbythesin2wmethod29.TheXraypeakbroadeningswereevaluatedfromthefullwidthathalfmaximumFWHMintegralvaluesafterremovaloftheKa2signal.TheFWHMvalueatthe90C176XrayincidenceangleoftheBraggdiffraction{220}peakswasusedasameasureoftherelativedislocationdensity29,orworkhardeningrate.TomeasurethecoreresidualstressthematerialwasremovedlayerbylayerbyanelectrolyticpolisherProtoManufacturingInc..TheelectrolyticpolishingmediumwastheA1solutionfromProtoManufacturingInc.Toinvestigatethethermalstabilityofthecompressiveresidualstressthesampleswereputinafurnaceat350C176Cfordifferentannealingtimesandthentheresidualstressmeasured.Toinvestigatethecyclicstabilityofthecompressiveresidualstresstheresidualstresswasmeasuredafterdifferentnumbersofroundsofcyclicloading.2.3.3.TemTheTEMsampleswerepreparedbythefocusedionbeamFIBliftoutmethod30inaFEINovaLab200FIBsystem.TEMwascarriedoutinanFEITitanoperatedat300keV.2.3.4.FatiguetestA100KNMTSservohydraulicfatiguetestingmachinewasusedtocarryoutthethreepointbendingfatiguetest,inloadcontrolmode.Theloadingprofileisasinewavefunctionwithafrequencyof5Hz.ThestressratioRis0.1forallthefatiguetestsi.e.Rrmin/rmax,whererministheminimumstressandrmaxisthemaximumstress.Themaximalbendingstresswascalculatedbyr¼3PL2bh2,wherePistheappliedload,Listhespanforthebendingfatiguetestsetup,bisthewidthofthespecimenandhisthethicknessofthespecimen.Allthetestswerecarriedoutatroomtemperatureandinalaboratoryenvironment.3.Resultsanddiscussion3.1.Processconditionsforwarmlasershockpeening3.1.1.LaserprocessingconditionOneofthemostimportantparametersinLSPislaserintensity,whichcontrolstheshockpressure.InthisstudyBK7glassshockimpedance1.44e6gcmC02sC0131wasusedastheconfiningmedium,whichhasamuchhighershockimpedancecomparedwithwatershockimpedance0.1655e6gcmC02sC0132.AccordingtoFabbroetal.33thelaserinducedshockpressurecouldbeestimatedasPðGPaÞ¼001ffiffiffiffiffiffiffiffia2aþ3pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiZðgcm2sÞpffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiI0ðGWcm2Þp,whereaisthatportionofabsorbedenergycontributingtothethermalenergyoftheplasmaandZ2Z¼1Z1þ1Z2isthereducedshockimpedancebetweenthetargetmaterialsteel4140shockimpedance3.96gcmC02sC01,estimatedasZqD,whereqisthematerialdensityandDistheshockvelocity34andtheconfiningmedium.FromourcalculationstheshockpressureusingBK7astheconfinementwasabout2.7timeshigherthanthatusingwaterastheconfinement.Inthisstudythelaserintensitiesusedwerefrom1.5to4GWcmC02witha0.5GWcmC02interval.Itwasfound5920111014–1025thattheconfiningmediumBK7glasscrackedatlaserintensitiesabove4.0GWcmC02.TheresidualstressesforstressareveryclosebetweenLSPandWLSP,i.e.WLSPFig.2.SurfaceresidualstressesforLSPandWLSP250C176Catdifferentlaserintensitiesandcorrespondingpeakplasmapressures.Fig.3.Hardnessatdifferenttemperatureslaserintensity4GWcmC02.C.Yeetal./ActaMaterialia5920111014–10251017laserintensitiesfrom1.5to4.0GWcmC02underLSPandWLSPconditionsweremeasuredFig.2.TheestimatedpeakplasmapressureatdifferentlaserintensitieswerealsoplottedbasedonFabbrosmodel33seeFig.2.ItwasfoundthattheresidualstressmagnitudesincreasedalmostlinearlywithincreasinglaserintensityforbothLSPandWLSPfrom1.5to4.0GWcmC02.Inaddition,theresidualstressmagnitudesforLSPandWLSP250C176Careverycloseatalllaserintensities.Thecompressiveresidualstressmagnitudesreacharound500MPaforbothLSP501MPaandWLSP519MPaat4GWcmC02.Whileahighmagnitudeofcompressiveresidualstressisbeneficialforfatigueperformance,4GWcmC02waschosenasthelaserintensityinthefollowingexperimentsinthisstudy.AccordingtothestudybyJuijerm23,themagnitudeoftheresidualstressgeneratedbydeeprollingathightemperature250C176Cismuchlowerthanthatatroomtemperature50comparedwith260MPa.ThusitisworthmentioningthatthemagnitudesofcompressiveresidualFig.4.Initialmicrostructureofquenchedandtemperedsteel4140withoutprecipitates.didnotreducethemagnitudeofresidualstresscomparedwithLSP.However,whatismoreimportantisthestabilityofresidualstress,whichwillbeaddressedlater.3.1.2.WLSPworkingtemperatureItisnecessarytodeterminetheoptimalworkingtemperatureforWLSPintermsofcompressiveresidualstressmagnitudeandhardnessimprovement.AccordingtowarmSPworkonAISI4140steelbyMenigandSchulze27anoptimalpeeningtemperatureof300C176Cwasidentified.ConsideringthattheDSAtemperatureofmediumcarbonsteelisbetween150C176Cand300C176C,temperaturesfrom100C176Cto350C176Cwithanintervalof50C176Cweretestedinthisstudy.ItwasfoundthatLSPatalltemperaturesleadstoanimprovementinhardnesscomparedwithLSPatroomtemperatureseeFig.3.Forallexperimentsbelow300C176Cthehardnessincreaseswithincreasingtemperature.ThisisbecausehighertemperaturesleadtoahighermobilityofthesoluteatomsandthusmoreefficientDSA17.ThepeeningshowingaretainedmartensiticlathsandbFe3Ccementite

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