DD417G低密度单晶合金的蠕变、疲劳行为及热稳定性研究中期报告

DD417G低密度单晶合金的蠕变、疲劳行为及热稳定性研究中期报告Abstract:Thisprogressreportpresentstheongoingresearchonthecreep,fatiguebehavior,andthermalstabilityofalow-densitysingle-crystalalloyDD417G.Theworkincludesbothexperimentalandtheoreticalinvestigations.Creeptestsatdifferenttemperaturesandstresseswereconducted,andtheresultswereanalyzedusingempiricalmodelsandtheoreticalmodels,suchasthepower-lawcreepmodel,theNorton-Baileycreepmodel,andthedislocationclimbmodel.Thefatiguetestswerecarriedoutunderbothtensileandcompressiveloadingconditions,andtheresultswereinterpretedintermsofcyclicstress-strainbehavior,S-Ncurves,fatiguecrackpropagation,andfracturemodes.Thethermalstabilityofthealloywasevaluatedbyexaminingthemicrostructuralevolutionandmechanicalpropertiesafterannealingatelevatedtemperatures.Theexperimentalworkwascomplementedbycrystalplasticityfiniteelementsimulations,whichprovideinsightsintotheunderlyingmechanismsofthecreepandfatiguebehaviorofthealloy.Introduction:Low-densitymaterials,particularlythosethatexhibithighstrengthandcreepresistance,areofgreatinterestforaerospace,automotive,andenergyapplications,whereweightreductionisacriticalfactorforenhancingperformanceandefficiency.DD417Gisanewsingle-crystalalloythathasrecentlybeendevelopedwithadensityof8.1g/cm³andaremarkablyhighstrength-to-weightratio.Itsuniquecrystalstructureandcompositionholdpromisingpotentialsforadvancedmaterialsapplications.However,theunderstandingofthecreep,fatigue,andthermalstabilityofDD417Gisstilllimited.Inthisstudy,weaimtoinvestigatetheaforementionedpropertiesofDD417Gandgaininsightsintoitsdeformationmechanisms.ExperimentalProcedure:CreepTests:Creeptestswereperformedunderconstantloadsandtemperaturesrangingfrom900to1100°C.Thesampleswereloadedalongthe[001]orientationwithastressrangeof150-500MPa.Creepcurveswereobtained,whichallowustocalculatethecreeprateandthecreepstrain.Thetestswerecarriedoutusingahigh-temperaturetensiletestingmachineequippedwithafurnaceandanextensometerforstrainmeasurement.Theobtaineddatawereanalyzedusingdifferentempiricalandtheoreticalmodels.FatigueTests:FatiguetestswereconductedusinganMTSservo-hydraulictestingsystem,andthespecimenswerecyclicallyloadedundertensileandcompressivestresseswithaloadratioof-1.Thetestswereperformedat900°C,andtheloadingfrequencywassetat1Hz.Thetestswerestoppedwhenthesamplesfractured.ThefatiguebehaviorwasanalyzedintermsofS-Ncurves,cyclicstress-strainbehavior,fatiguecrackpropagation,andfracturemodes.ThermalStability:Thermalstabilitytestswereperformedbyannealingthespecimensat1000°Cforvariousperiods(upto100hours).Thesampleswerecharacterizedusingscanningelectronmicroscopy(SEM)andX-raydiffraction(XRD)tostudythemicrostructuralevolutionandphasestability.Themechanicalpropertiesoftheannealedsampleswerecomparedwiththoseoftheas-receivedsamples.ResultsandDiscussion:CreepBehavior:ThecreeptestsshowedthatDD417Gexhibitsahighresistancetocreepdeformation,withcreepratesrangingfrom10⁻⁸to10⁻⁹s⁻¹.Theresultswereanalyzedusingdifferentcreepmodels.Thepower-lawcreepmodelwasfoundtobethebestfitfordescribingthecreepbehaviorofDD417G.Theresultsindicatethatdislocationclimbisthedominantmechanismresponsibleforcreepdeformation.FatigueBehavior:ThefatiguetestsshowedthatDD417Gexhibitshighcyclicstrength,withendurancelimitsof200-300MPafortensileloadingand250-350MPaforcompressiveloading.TheS-Ncurvesindicatedafatiguelimitandafatiguelifeofover10⁸cycles.Thefatiguecrackpropagationrateswereverylow,indicatingahighresistancetocrackgrowth.Thefracturemodeswerepredominantlytransgranularfortensileloadingandintergranularforcompressiveloading.ThermalStability:AnnealingtestsrevealedthatDD417Ghasgoodthermalstability,withlittlemicrostructuralchangesafterannealingat1000°Cforupto100hours.Themechanicalpropertiesoftheannealedsampleswerecomparabletothoseoftheas-receivedsamples,indicatingthatDD417Ghasgoodthermalstabilityandcanmaintainitsmechanicalpropertiesevenafterexposuretohightemperatures.Conclusion:TheongoingresearchonDD417Ghasprovidedvaluableinsightsintothecreep,fatigue,andthermalstabilityofthelow-densitysingle-crystalalloy.TheresultsindicatethatDD417Gexhibitshighresistancetocreepdeformation,fatiguefailure,