27 Superalloy Case Study.ppt

530.352MaterialsSelection,Lecture#27:SuperalloyCaseStudyWednesdayNov16th,2005,TheBoeing777,PoweredbytwoGE90s,777sarepoweredby2GE90s:,LowPressureTurbine,HighPressureTurbine,Combustor,HighPressureCompressor,LowPressureCompressororBooster,Fan,FanAir,CoreAir,GE90JetEngine:,Efficiencyofaheatengine,Threewaystoincreaseefficiency:,DTBC,Improvementsinsuperalloycreepstrength:,Improvementsincreepstrength:,Alloydevelopmentbasedonfundamentalunderstandingofcreepappliedempirically.Formstableprecipitates(Ni3Al,Ni3Ti,M23C6,MoC,TaC)Haveasmanyheavyatomsinsolidsolutionaspossible(Hf,W,Co,Cr,Ta,etc.)Formaprotectiveoxidesurface(Cr2O3orAl2O3),Improvementsincreepstrength:,10mm,1mm,Secondaryg,Tertiaryg,Primaryg,Supersolvusheattreatment(no“primary”g)SecondarygdevelopsuponcoolingfromsupersolvustemperatureTertiarygformsuponcoolingandsubsequentaging,Microstructuredevelopment:,Ref.Millsetal,Superalloydevelopments:,Improvementsincreepstrength:,Changinggrainsizetomitigatecreep:,Equiaxed,Directionalsolidification,Singlecrystalturbineblade,Makingsingle-crystallineturbineblades:,Investmentcasting:,Sectionofabladewithcoolingchannels:,Internalcoolingchannels:casting:,“TBCsarebill-of-materialsinmanyGEAEproductlines:turbineblades,vanes,combustors.Designersloveit,andwantmore.”,EnginerunwithoutTBC,EnginerunwithTBC(150Freduction),Ref.RamDarolia,GEAircraftEngines,IndustrialperspectiveontheuseofTBCs:,StrengtheningofGammaTiAl:ProsandCons,CurtAustinandJimWilliamsTMSAnnualMeetingSanAntonio,TX2/17/98,AircraftEngines,g,OutlineofTalk,IntroductiontostrengtheningDefinitionPropertycorrelations:creep/yieldstrength;fatigue/yieldstrength;etc.Limitations,pertytrades&compromisesNeedsandapplicationsGeneraldiscussionofstrengtheningofGammaMechanismsTrade-offsBenefitsand“costs”ConsequencesofstrengthenedGammaDuctilityFatiguestrengthSummaryandConclusions,Strengthening,NarrowDefinition:Alterationsinthecompositionand/ormicrostructurethatincreasethetimeindependentflowstressatsmallplasticstrain(theyieldstress)BroaderDefinition:Alterationsinthecompositionand/ormicrostructurethatincreasethetimedependentflowstressatsmallplasticstrain(thecreepstrength),Theavailablemechanismsandopportunitiesforthesetwostrengtheningmodesarequitedifferent,EffectsAlloyingonProperties,DuctilityCr,Mn,VOxidationResistanceCr,Nb,Ta,ZrTensileStrengthCr,Ta,W,BCreepResistanceCr,W,Ta,C,Si,Somealloyingelementsaffectmorethanoneproperty,StrengthImprovement,Notdifficulttoimprovestrength:-mechanismsavail.Improvedstrengthwithconstantductilityverydifficult(complexissue)DKthincreasealsoreqd.torealizefullbenefit,AvailableStrengtheningMechanisms,SolidsolutionGenerallylowsolubility,secondphasescanbeharmfulNotamajorcontributorBoundaryStrongestcontributorCanuseheattreatmenttotailorstrength(withinlimits)Texture(preferredorientation)PossibleinprincipleforwroughtproductsDifficulttocontrolcost?Magnitudeofeffectnotwell-characterizedSecondphaseparticlestrengtheningRelativelylowGfinedispersionformuchstrengtheningCoarseningcouldbeanissue,Thereal“player”isboundarystrengthening,DuctilityVs.YieldStrength,IncreasingYieldStrengthhasalargeeffectonductility,FractureSurfacesinTi-48.9%Al,Transgranular,interdendriticfracturemode,withB2(1.2%elong.),withoutB2(1.5%elong.),B2,DuctilityofGamma-Issues,MajornegativedistinctionfromconventionalalloysCarefulcomponentselectioneliminatesthistechnicalconcernStillapsychologicalissuewithdesignersRequirementoftennotexplicitlyknownSeecomponentselectionaboveUsefulfor“margin”and“robustness”OftenimplicitlyrequiredatstressconcentrationsNeedenoughtorelaxstresswithoutcrackinitiationVeryhelpfulinavoidinghandlingandimpactdamageExplicitlyrequiredinafewcomponentsrotoroverspeedrelativelysmallamountrequired(but0!)containment,appliestocasingapplications,Ductilityisabiggerperceivedthanrealissue,Ductilityasf(Al,dT/dt),%Elong.,45,46,47,48,49,Allevel,a/o,Fractureasf(Al,dT/dt),Cr-Nb-Taassessedeffectsonductility,Deltalogelong.,Atomicpercent,Cr,Ta,Nb,B2erdendriticembritt.,Interdendriticstrengthening,Twodistinctdomainsincastalloys,YieldStrengthvs.HCFStrength,Dataforseveralalloysandseveraltemperatures,LimitingPropertyOftenDKth,Material1:Lofatiguestrength,BaselineFCG,baselineDKth(4.35)Material2:Hifatiguestrength,BaselineFCG,baselineDKthMaterial3:Hifatiguestrength,LowerFCG(0.4x),baselineDKthMaterial4:Hifatiguestrength,LowerFCG(0.4x),higherDKth(5.0),Life(Cycles),Max.Stress(ksi),Material4,th,80,Materials1,2,&3,fromKenWright,GE,Fat.Strength:Material1Materials2,3&4,FCG:Material1,2Material3,4,As-castsegregationpattern,Sutliffe,HuangandSitzman,NCG359E,0.15%elong,47Al-1.8Cr-0.8Nb-1.7Ta,0.6%elong,Highimpurityheat,LowAlheat,SpeculationRegardingCreep,Alloyingeffects:CrispotentstrengthenerStrengthensgammaVeryfineB2pptsmaybegoodNbHeavysoluteatomeffectoutweighedbyreducedgrainsizeTaHeavysoluteeffectoutweighsreducedgrainsizeMicrostructureeffects:GrainsizeisimportantGrainaspectratiomaybeimportantSecondphasecoarseningnotwellunderstood,Hardtoseparatecompositionandmicrostructurecontributions,SomePropertyCorrelations,Directcorrelations:Strength-HCFstrengthStrength-PartcostParticularlytrueforwroughtprocessingInversecorrelations:Strength-DuctilityDuctility-CrackgrowthCreep-DuctilityCaveat:AboveobservationscoloredbyGEfocusoncastmaterial,but:someveryinterestingwroughtpropertiesobtainedrecentlyGEfollowingcloselythoserelatedtocomponentsforwhichwroughtprocessingisamenableandaffordable.,BladeStatus,DesignreleasedCastingtrialsnearingcompletionRiskissuesunderstudyEconomicalproductionismajorconcern,SummaryandTake-aways,StrengtheningofGammaispossible:Standardmechanismspertain(tovaryingdegrees)Increasedstrengthhurtsductility:ComponentselectiontominimizeriskisessentialNeedtodealwithperceive