Characterization of Steels by Anomalous Small-Angle X-ray Scattering

154 Pages·2010·3.12 MB·English

Characterization of Steels
by
Anomalous Small-Angle X-ray Scattering
PeterRene´ Jemian
June1990
ii
(cid:13)c CopyrightbyPeterRene´ Jemian,1990
AllRightsReserved
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Abstract
CharacterizationofSteelsbyAnomalousSmall-AngleX-rayScattering
PeterRene´ Jemian
ThesizedistributionandvolumefractionofCr C havebeenisolatedfromthedistributionsofallotherprecipi-
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tatesinagedsamplesofaferriticalloy,ModifiedFe9Cr1Mosteel,bythetechniqueofanomaloussmall-angleX-ray
scattering(ASAXS),inwhatisbelievedtobethefirstapplicationofthistechniquetoprecipitationinanengineering
alloy. Thesteelhasbeenproposedforuseatelevatedtemperaturesforlongtimesinpowergenerationequipmentand
the stability of the microstructure must be verified. Six samples were aged for 5000 hours at either room tempera-
ture, 482, 538, 593, 649, or 704◦ C to simulate a typical in-service condition. Synchrotron radiation was used as a
variable-wavelength source of X-rays. Three X-ray wavelengths near the Cr K absorption edge were used to vary
the scattering contrast of Cr C while leaving that of the other precipitates fixed. A double-crystal diffractometer
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and a silicon photodiode X-ray detector were specially designed for use atthe synchrotron to measure the scattered
radiation. Thethreesmall-anglescatteringcurvesfromeachsamplewereanalyzedbyamaximumentropytechnique
toobtainthreescatteringcontrast-weightedsizedistributionsofalltheprecipitatesthatgiverisetotheobservedscat-
tering. AscatteringcontrastgradientanalysiscombinedthethreeexperimentstoisolatetheCr C volumefraction
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distributions. The mean diameter of Cr C particles was found to increase with temperature for 5000 hour aging
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between538and704◦C,consistentwithpriortransmissionelectronmicroscopyresults.
Theultra-highstrengthsteelalloyAF1410,currentlyusedforarrestinghooksoncarrier-basedaircraft,derivesits
desirablepropertiesbyadelicateheattreatmentthatcarefullybalancestheformationofonecarbidewiththedepletion
ofanother. ThelackofASAXSneartheCrandFeK absorptionedgesindicatesthatthedistributionsofprecipitates
observed(presumablyM Candaustenite)areiron-enrichedandchromium-deficient.
3
ApprovedbyProfessorJuliaR.Weertman
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v
Preface
ceiiinosssttuv-RobertHOOKE,1676
Chapter1providesinformationabouttheASAXSinvestigationsofotherworkersandalsosomebackgroundonthe
twosteelalloysinvestigatedbytheASAXStechnique. InChapter2,thetheoryunderlyingsmall-anglescatteringand
thespecificASAXSapplication, equationsthatdescribethedesignandoperationoftheDCDoptics, theprocessof
resonantRamanscattering,andageneraldescriptionofthesiliconphotodiodedetectoraregiven. Theexperimental
equipmentandprocedurearedescribedinChapter3. Chapter4describestheexperimentalcommissioningofthenew
DCD and photodiode detector using the scattering of polystyrene spheres and bulk microporous silica. Also given
there are the SAXS and ASAXS results for the two steels alloys being investigated. These data are summarized in
Chapter 5 and suggestions for future investigations with the DCD are presented. In the first appendix, the results
of SAXS experiments on other materials of interest in materials science are given. These materials are bulk micro-
TM
porous silica and porous Vycor glass. Other appendices contain the electrical schematics for the Si photodiode
detector,thecomputerprogramsforcollimationcorrection,Lake.FOR,andinterpretationofsmall-anglescattering,
MaxSAS.FOR,andtheexperimentalSAXSdataforthesteels.
SI units are reported throughout with the exception of degrees Celsius, rather than Kelvins, and mass density in
g·cm−3. The wavelength, λ, of X-ray photons is described in terms of their photon energy, E, where the relation
Eλ = 1.239857804 nmkeV isused. Usageof nomenclaturewillbe keptconsistent withineach sectionofthe text
orexplicitlynoted. Forstyle,thisworkfollowsguidelinessetforthbyMichaelson,98 butalsotakesadvicefromthe
remarksofMermin.97 Argumentsoncomputerprogrammingstyle15,17,100werealsoconsidered.
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Acknowledgements
uttensiosicvis-RobertHooke,1678
Iamgratefultomyadvisor,ProfessorJuliaR.Weertman,forherencouragement,guidance,andfinancialsupport
throughout this study. I would like to express my great appreciation to Dr. Gabrielle G. Long of the National Insti-
tuteofStandardsandTechnologyfornumerousilluminatingdiscussionsandmany∞ longhoursatthesynchrotron.
Additionally, I would like to thank Dr. Joe Georgopoulos for materials, advice, and assistance in the early stages
of this project and Dr. Greg Olson for samples and helpful advice. Special thanks go to Mr. Rich Matteson for ad-
vising a change of career from jazz music. I think he would be proud. This research was supported by the United
States Department of Energy under grant DE-FG02-86ER45229. Dean J. B. Cohen is to be acknowledged for his
initial suggestion that anomalous dispersion might be used to separate the small-angle scattering from one type of
scattererinamulti-componentalloy. FromtheOakRidgeNationalLaboratory,Dr.VinodSikkaisacknowledgedfor
providing the Modified Fe9Cr1Mo steel, Dr. George Wignall and Dr. S. Spooner for conducting small-angle X-ray
scatteringmeasurementsattheNationalCenterforSmall-AngleScatteringResearch,andDr.A.Habenschussforthe
fPrime.FOR code which was obtained via Dean J. B. Cohen. The UKAEA-Harwell laboratory is acknowledged
fortheMaxe.FORmaximumentropySASanalysiscode. Dr.RichardD.SpalofNISTistobeacknowledgedforhis
supportoftheexperimentalphasebyprovidingassistanceatthesynchrotronbeamline.
TothemembersoftheAll-NightScatteringCrewatthesynchrotronwhoengagedthemselvesinapracticalstudy
ofthelong-termeffectsatambienttocryogenictemperaturesoflow-cyclefatigueofmaterialsscientists: Dr.Andrew
Allen,Dr.DavidBlack,Dr.DidierGavillet,Dr.GabrielleLong,Dr.JuliaWeertman,Mr.JohnBarker,andMr.Kishio
HidakaaretobecommendedfortheirabilitiestofighttheFourAMfatigue. SpecialthanksgotoMr.HaroldHalof
theGoldenHandsBurdetteofNISTforassistanceindesign,mechanics,andconstructionoftheDCDSAXScamera.
Appreciation is extended to my colleagues at Northwestern University, both past and present for their valuable
discussion, friendly harangues, and general camaraderie. Particular thanks go to Mr. Mike Verrilli whose graphical
machinationswithSASdataprovidedtherealizationofhowtoprocesstheSASdatamoreefficiently. Also,special
thanks are extended to the personnel in the Chemistry Department Electronics Shop (especially the late Mr. Jim
Baker),MaterialsScience“world’sfriendliest”MachineShop,MetallographyLab,TEMfacility,andX-raydiffraction
facility.Lastbutnotleast,Iacknowledgetheguidanceofmyparentswhoatkeybifurcationpointsinmydevelopment
providedagentlenudgeorevenastrongtuginwhattimehasproventobetherightdirection.
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Contents
1 Introduction 1
1.1 AnomalousDispersionSmall-AngleX-rayScattering(ASAXS) . . . . . . . . . . . . . . . . . . . . 1
1.1.1 MetallurgicalApplications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1.2 OtherApplications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 SteelAlloyDescriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2.1 ModifiedFe9Cr1MoSteel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2.2 AF1410Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 Theory 7
2.1 Small-AngleScattering(SAS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1.1 BasicSASTheory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1.2 ScatteringfromSphericalParticles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1.3 InstrumentalCollimationCorrection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1.4 SizeDistributionAnalysisbyMaximumEntropyTechnique . . . . . . . . . . . . . . . . . . 11
2.2 AnomalousDispersionSmall-AngleX-rayScattering(ASAXS) . . . . . . . . . . . . . . . . . . . . 14
2.2.1 AnomalousDispersionandtheDispersionCorrections . . . . . . . . . . . . . . . . . . . . . 14
2.2.2 ScatteringLengthDensity,Contrast,andStrength . . . . . . . . . . . . . . . . . . . . . . . . 15
2.2.3 ExperimentRequirementsforASAXS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.2.4 LimitsofDetectability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.2.5 IsolationofaSingleScattererbyASAXS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.3 ResonantRamanScattering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.4 Double-CrystalDiffractometerCamera(DCD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.4.1 Bonse-HartDesign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.4.2 OptimizationoftheOpticsfortheSynchrotronSource . . . . . . . . . . . . . . . . . . . . . 24
2.4.3 RockingCurveCalculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.4.4 AsymmetricReflection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.5 SiliconPhotodiodeDetector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.5.1 PrinciplesofOperation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.5.2 AmplifierElectronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3 Experimental 31
3.1 SteelSamples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.1.1 HeatTreatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.2 SAXSSamplePreparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
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3.3 Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.3.1 X-raySource . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.3.2 Monochromator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.3.3 ExperimentalHutch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.3.4 BeamTransportandIncidentBeamMonitor . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.3.5 Double-CrystalDiffractometerAnalyzerMonolith . . . . . . . . . . . . . . . . . . . . . . . 34
3.4 SiliconPhotodiodeX-rayDetector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.5 ComputerDataAcquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.6 DataReduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.7 RawData . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.8 AbsoluteIntensityConversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.9 Slit-LengthDesmearing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.10 SizeDistributionAnalysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
4 ResultsandDiscussion 41
4.1 ValidationofEquipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.1.1 PolystyreneSpheres: 255and460nmdiameters . . . . . . . . . . . . . . . . . . . . . . . . 41
4.1.2 SiliconPhotodiodeDetectorvs. ScintillationCounter . . . . . . . . . . . . . . . . . . . . . . 43
4.1.3 AbsoluteIntensityCorrelation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
4.1.4 Slit-WidthCorrection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.2 ModifiedFe9Cr1MoSteel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.2.1 SampleThicknessMeasurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.2.2 MeasurementofAnomalousDispersionCorrections . . . . . . . . . . . . . . . . . . . . . . 49
4.2.3 ScatteringStrength-WeightedSizeDistributionAnalyses . . . . . . . . . . . . . . . . . . . . 52
4.2.4 CalculationoftheScatteringContrasts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
4.2.5 Cr C VolumeFractionDistributionIsolatedbyASAXS . . . . . . . . . . . . . . . . . . . 60
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4.2.6 SummaryofModifiedFe9Cr1MoSteelAnalyses . . . . . . . . . . . . . . . . . . . . . . . . 67
4.3 AF1410Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
4.3.1 ASAXSAnalyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
4.3.2 Austenitizedat1000◦C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
4.3.3 Austenitizedat830◦C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
4.3.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
4.3.5 SummaryoftheAF1410SAXSanalysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
5 Summary 77
5.1 SuggestionsforFutureWork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Appendix: OtherSamples 81
A BulkMicroporousSilica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
B PorousVycorTMGlass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Appendix: SiliconPhotodiodeDetector 85
C ImplementationoftheSiliconPhotodiodeDetector . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
D CircuitDiagramsfortheModularDetector. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87