Aero Engine Materials

Developmenthistory

Aeroenginematerialsarestructuralmaterialsusedinthemanufactureofmaincomponentssuchasaeroenginecylinders,pistons,compressors,combustionchambers,turbines,shafts,andexhaustnozzles.Intheearlystage,aeroenginesweremadeofaluminumalloy,magnesiumalloy,high-strengthsteelandstainlesssteel.Inthelaterstage,titaniumalloy,high-temperaturealloyandcompositematerialswereappliedinsuccessiontomeettheneedsofincreasingenginethrustandimprovingaircraftflightspeed.Inaero-engines,turbinebladesarelistedasthefirstkeycomponentbecausetheyareinthepositionwiththehighesttemperature,themostcomplexstress,andtheworstenvironment,andareknownasthe"jewelinthecrown".Theperformancelevelofturbineblades,especiallythetemperature-bearingcapacity,hasbecomeanimportantindicatoroftheadvancedlevelofamodelofengine,andinacertainsense,itisalsoasignificantindicatorofthelevelofacountry’saviationindustry.

Thedevelopmentofturbinebladematerials

Inthe1940s,theprincipleofjetengineshasbeenproposed,butthereisnosuitablehigh-temperaturematerialforthemanufactureofturbines,andthedevelopmentisslow.

Inthe1950sand1960s,theBritishWhiteCompanydevelopednickel-basedsuperalloys.Inaddition,thepurityofthehigh-temperaturealloyproducedbythevacuummeltingmethodisimprovedandtheperformanceisbetter.Aeroengineturbinebladesusedeformedsuperalloysandcastsuperalloys.

Inthe1970s,withthecontinuouspursuitofhighthrust-to-weightratiosforaeroengines,high-temperaturecomponentmanufacturingprocessessuchasdirectionalsolidificationandsinglecrystalcastingweredevelopedtofurtherimprovethemaximumoperatingtemperatureandfatigueresistanceoftheblades.Foreignactiveenginebladematerialsmainlyusesecond-generationandthird-generationsinglecrystalalloys.Thesesinglecrystalalloysarepronetoproducebrittlephasesduetotherichrhenium.Inrecentyears,ithasbeenstudiedtoaddrutheniumoriridiumtoreducethebrittlenesstendency,andthefourthgenerationofsinglecrystalalloyshavebeendeveloped.Thedevelopmenttrendofbladetechnologyistoconsiderthestructure,materialandprocessinaunifiedway,andusecastingandlaserdrillingprocessestodirectlymanufacturedivergentcoolingchannels.

Inthe1980s,thedevelopmentofceramicbladematerialsbegan.Inadditiontoimprovingthetemperatureresistanceofbladematerials,micro-laminatedcompositematerialscomposedofintermetalliccompoundsandductilemetalswereusedasthe"thermalbarriercoating"ofblades.Payattentionto.Thistechnologyreliesonhigh-temperature-resistantintermetalliccompoundstoprovidehigh-temperaturestrengthandcreepresistance,anduseshigh-temperaturemetalsastougheningelements,therebywellovercomingthebrittlenessofintermetalliccompounds.Severalmicro-levelmicro-laminatedcompositematerialshavebeendevelopedusingvacuumhot-pressedfoil,physicalvapordeposition,castingandsolid-statereactionmethods,includingNb-Cr₂Nb,NB-NbsSi₃andNB-MoSi₂etc.Micro-laminatednanothermalbarriercoatingsareexpectedtoincreasethetemperatureresistanceofbladesby260°C.Exceptforblades,micro-laminatedcompositematerialsareusedinfatigue-freealloycoatings,sand-resistantresin-basedcompositefanbladecoatings,etc.Therearealsoapplicationopportunities.

Thedevelopmenttrendofenginebladematerialsinmycountryisgood.Therearemorethan20kindsofmaterialsforcastingturbinebladesalone,andthedevelopmentofsinglecrystalnickel-basedsuperalloys,intermetalliccompounds,ceramicsandC/Ccompositematerialshasbeencarriedout.Theperformanceofthelow-density,low-costfirst-generationsinglecrystalalloyDD3inmycountryisequivalenttothatofthesame-generationforeignalloys,andhasbeenusedinsmallhelicopterengineturbineblades;thesecond-generationsinglecrystalsuperalloyDD6isbeingpromotedforuseinadvancedturbineengineblades.Itstemperaturebearingcapacityisequivalenttothatofforeignalloysofthesamegeneration,andthecostislower.Asfarasturbinediskmaterialsareconcerned,inadditiontothewidelyusedpowderdisksandtheirdevelopeddual-performancepowderdisksandthree-performancepowderdisks,fine-graindeformeddisksarealsofavoredduetotheirlowcost.TheRussianmanufacturingindustryinsiststhattheuseoftraditionalfusion-castdeformeddiscscanfullymeettheneedsofthefourthandfifthgenerationengines.Asanewturbinediscsolution,ajetdiscwithoutinclusionshasbeendevelopedinrecentyears.Comparedwiththepowdermetallurgyprocess,thistechnologyhastheadvantagesofsimplificationandcostreduction.Itsfast-settingmicrostructurehasestablisheditsperformanceadvantages,includingfarsuperiortothecastingandforgingprocess,thestrengthanddurabilityoftheequivalentorhighFpowdermetallurgyprocess,Betterplasticity,toughnessandlow-cyclefatiguelifethanpowdermetallurgyprocesses,andimprovedhotworkabilityduetograinrefinement.Sincealltheprocessingequipmentofthetraditionaldeformeddisccanbeused,thematerialutilizationrateishigh,andthecostissignificantlylowerthanthatofthepowderdisc.Therefore,thejetdiscmaybecomeastrongopponentofthepowderdisc.

Thedevelopmentofturbinediscmaterials

Inthe1940s,theturbineinlettemperaturewasabout800~900C°,whichused16-25-6iron-basedalloy.

Inthe1950s,astheturbineinlettemperatureincreasedto950°C,precipitationhardenedalloysappeared.Theprincipleofprecipitationstrengtheningwasappliedtomakethealloyshavehigherhightemperaturestrength.

Inthe1970s,theinlettemperatureincreasedto1240℃,andRene95alloyandpowdermetallurgysuperalloysappeared.

Intheseadvancedaero-engines,high-temperaturematerialsarestillthecoretechnology.Suchashigh-temperaturetitaniumalloys(compressordiscsandblades),high-temperaturealloyplates(combustionchambers),powdermetallurgymaterials,andsingle-crystalbladematerials(turbines)inmilitaryengines,andsingle-crystalbladematerialsandpowderedhigh-temperaturealloysusedincivilenginesTurbinediscmaterial.

Developmenttrend

Thematerialsforthehotendpartsoftheenginearemainlyhigh-temperaturealloys.Forexample,theapplicationoftitaniumalloybeganintheengine,anditisstillthemainmaterialoftheenginecompressor.Theintroductionofvacuumsmelting,directionalsolidificationandsinglecrystalcastingincreasedtheinlettemperatureoftheengineturbinefrom700°Cin1940to1,650°Cin2000,andtheservicelifeoftheenginewasalsogreatlyincreased.Inthenextstep,theturbineinlettemperaturewillincreasefrom1650°Cto1715°C,andmayriseto1977°Cafter2020.Inordertoachievethesedemandingrequirements,itisnecessarytorelyontheperfectcombinationofmaterials,processesandcoolingtechnology.

Animportantdevelopmenttrendofaeroenginematerialsistocontinuetodevelopnewthirdandfourthgenerationsinglecrystalalloys.ThefourthgenerationsinglecrystalalloydevelopedbyNASAhasanoperatingtemperatureof27～42℃higherthanthatofthethirdgeneration.TheIXC-55beingdevelopedinRussiaalsobelongstothefourth-generationsinglecrystal,anditsendurancestrengthat1100°Cfor100hisashighas180-190MPa.NASAalsoplanstoincreasetheoperatingtemperatureby56°Ccomparedtothefourth-generationsinglecrystal,whichisveryclosetothemeltingpointofthealloy.Inaddition,nickel-aluminumalloysarealsooneofthedevelopmentdirections.

Highertemperaturealloysaccountfor55%-65%ofmoreadvancedengines,andtheamountoftitaniumalloysis25%-40%.Thethrust-to-weightratiooftheenginehasreached10,andtheturbineinlettemperaturehasreached1650℃.Tofurtherincreasethethrust-to-weightratioofengines,wemustfirstdevelophigh-temperaturestructuralmaterials,suchasintermetallicmaterials,metalmatrixcomposites,ceramics,andC/Cmatrixcomposites.Therefore,thesematerialshavealwaysbeenthefocusofresearchonaero-enginematerials..

Materialcharacteristics

Thecharacteristicsofaeroenginesaresmallsize,highpower,andtheworkingconditionsofeachcomponentareharsh,especiallywhentherotatingpartsareexposedtodifferenttemperatures,loads,andenvironmentalmedia(air,Forworkingundergas),mostofthemmustbemadeofmaterialswithhighspecificstrength,goodheatresistanceandstrongcorrosionresistance.Theservicelifeofaeroenginesisnotthesame.Militaryaircraftenginesgenerallylastfrom100to1,000hours;civilaircraftenginesevenrequiremorethan10,000hours,andthestructureandperformanceofthematerialsusedmustremainstableforalongtime.Intheearlystage,aeroenginesweremadeofaluminumalloy,magnesiumalloy,high-strengthsteelandstainlesssteel.Inthelaterstage,titaniumalloy,high-temperaturealloyandcompositematerialswereappliedinsuccessiontomeettheneedsofincreasingenginethrustandimprovingaircraftflightspeed.

Thefirstpropeller-typeaircraftwasequippedwithapiston-typeaeroenginemadeofcastaluminumalloyandalloysteelin1903.Fromthe1940stotheearly1950s,withsuperalloys,theturbojetenginewassuccessfullydeveloped,enablingtheaircrafttoflyfasterthanthespeedofsound.Inthe1960s,duetotheapplicationanddevelopmentofcastsuperalloysandtitaniumalloys,turbofanenginesweresuccessfullydeveloped.Inthe1970s,theemergenceofdirectionalsolidificationsuperalloyhollowturbineblades,powderedsuperalloyturbinedisksandnewtitaniumalloysincreasedtheturbineinlettemperatureto1370°C,andthethrust-to-weightratiooftheturbofanenginereachedmorethan8.

Piston-typeaeroenginecylindersaregenerallymadeofmediumcarbonchromium-molybdenum-aluminumsteelwithastrengthof1000MPa(about100kg/mm)tofacilitatesurfacenitriding,improvewearresistanceandcorrosionresistancesex.Thepistonismadeofforgedaluminumalloywithastrengthof300MPa(about30kg/mm),andthenembeddedwithalloycastironexpansionrings,whichplayaroleofwearresistanceandsealing.Theconnectingrodandcrankshaftaremadeofhigh-qualitychromium-nickelalloysteel,andthepartsrequiringwearresistancearealsocarburizedornitrided.

Theoperatingtemperatureofthecompressorpartsoftheturbojetengineisgenerallylowerthan650℃,anditisrequiredtobemadeofmaterialswithhighspecificstrengthandfatiguestrength,impactresistanceandcorrosionresistance.Theimpellerofthecentrifugalcompressoruseshigh-strengthaluminumalloy.Titaniumalloyisusedforthefrontfanbladesofaxialcompressors.Thewheelsandbladesoflow-pressurerotorsusesteelandaluminumalloys,andthedevelopmenttrendistousealltitaniumalloys.High-pressurerotordiscsandbladesuseheat-resistantsteel,andthedevelopmenttrendistousehigh-temperaturealloys.Thefrontcasingismadeofsteelortitaniumalloy,andsomecasingsalsoneedsound-absorbingmaterialsforsoundinsulation.Thetemperatureofthecombustionzoneinthecombustionchamberisashighas1800~2000°C.Despitetheintroductionofairflowcooling,thewalltemperatureofthecombustionchamberisgenerallyabove900°C.Itisusuallymadeofeasilyformedandweldablehigh-temperaturealloy(newnickel-basedandcobalt-basedalloy)plates..Inordertopreventgaserosion,thermalcorrosionandheatinsulation,protectivecoatingsareoftensprayed.Dispersion-strengthenedalloyscanbeusedtomakecombustionchambersresistantto1200°Cwithoutcoating.Thematerialsusedinthecombustionchambercanbeusedtomaketheafterburnerandthetailnozzle.Thematerialsusedtomaketurbinebladesandturbinedisksareimportantmaterialsthataffectengineperformance.Suitablematerialsformanufacturingturbinebladesarecastnickel-basedalloys.Theturbineinlettemperatureofmodernexperimentalengineshasreached1650°C,andthehigherrequirementhasreached1930°C.Thedevelopmentoforientedsinglecrystal,orientedeutectic,tungstenwire-reinforcednickel-basedalloysandceramicmaterialsisunderway,anddispersion-strengthenednickel-basedalloysandnewpowderturbinediskalloysarebeingdevelopedtomeettheneedsofmoreadvancedengineturbinebladesandturbinedisks.