Fundamentals of Radiation Materials Science: Metals and Alloys

839 Pages·2007·30.62 MB·English

by  Gary S. Was

FundamentalsofRadiationMaterialsScience
Gary S. Was
Fundamentals
of Radiation
Materials Science
Metals and Alloys
With381 Figures
123
GaryS.Was
NuclearEngineeringandRadiologicalSciences
MaterialsScienceandEngineering
UniversityofMichigan
1921CooleyBldg.
2355BonisteelBlvd.
AnnArbor,MI48109-2104,USA
e-mail:[email protected]
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ISBN 978-3-540-49471-3 SpringerBerlinHeidelbergNewYork
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Preface
Thepurposeofthistextistoprovideafoundationforunderstandingthetheoryand
mechanisms behind the effects of irradiation on metals and alloys. The subject is
divided into three parts, each of which is subdivided into individualchapters that
together, provide a unified picture of how radiation interacts with, and alters the
structureandpropertiesofmetallic materials. PartI consistsof threechaptersand
focusesontheradiationdamageprocessandprovidestheformalismforthepredic-
tionoftheamountandspatialconfigurationofthedamageproducedbybombarding
particles.Chapter1treatstheinteractionsbetweenparticlesthatresultinthetransfer
of energyfrom the incidentparticle to the targetatoms. Chapter 2 focuses on de-
terminationofthenumberofdisplacementsproducedbythebombardingparticles,
andChap.3describesthespatialconfigurationsoftheresultingdefects.
While radiation damage describes the state of the irradiated material, radia-
tioneffectsareconcernedwithdefectbehaviorinthesolidafterformation.PartII
(Chaps. 4–11) covers the physical effects of irradiation on metals. Chapter 4 pro-
vides backgroundon the equilibrium concentration of point defects and their dif-
fusion. Chapter 5 treats diffusion and reactions between point defects under irra-
diation that are fundamental to all of the observable effects. Chapter 6 describes
radiation-inducedsegregation,whichisadirectconsequenceofradiation-enhanced
diffusion.Chapters7and8addressthenucleationandgrowthofdislocationloops
andvoids,thedefectaggregatesthatdeterminemuchof thebehaviorofirradiated
alloys. Chapter 9 covers the stability of phases under irradiation and irradiation-
inducedprecipitationandprecipitatedissolution.Chapter10extendstheeffectsof
irradiationtotheuniqueeffectsresultingfromionirradiationsuchascomposition
changes,sputtering,exfoliation,etc.Finally,Chap.11describestheapplicationof
ionirradiationtosimulatetheeffectsofneutronirradiation.
Mechanicaleffectsofradiationdamage(PartIII)aredistinguishedfromphysical
effectsbytheapplicationofstress.Hardeninganddeformationofalloysunderirra-
diationarediscussedinChap.12.Theeffectofirradiationoncracknucleationand
propagationresultingeitherfromstaticorfatigueloadingisdiscussedinChap.13.
Finally,creepdeformationandgrowtharetreatedinChap.14.Irradiationalsohas
aprofoundeffectoncorrosionandstresscorrosioncrackingandthesedegradation
modes may prove to be limiting processes for many reactor designs. Chapter 15
combinesthe effects of irradiation with the processes of corrosion and stress cor-
rosioncrackingtoexaminehowirradiationandthemediacancombinetodegrade
alloybehavior.
VIII Preface
Thechapterscontainexamplesandillustrationsofradiationeffectsandsample
calculationstoquantifyanddescribetheobservations.Problemsattheendofeach
chapteraredesignedtoreinforcethemainconceptsofeachchapterandtochallenge
thereaderonhisorhercomprehensionofthetopicscoveredwithin.Takentogether,
thechaptertext,examples,illustrationsandend-of-chapterproblemsprovideacom-
prehensivetreatmentoftheeffectsofirradiationonmetalsandalloys.
The subjectmatter in this text will likely require two academic terms to com-
plete. Many of the topics rely on a basic knowledge of disciplines that constitute
theunderlyingbasisforirradiationeffects:thermodynamicsandkineticsofsolids,
crystalstructure,defectsanddislocations,physicalmetallurgy,elasticity andplas-
ticity, deformation and fracture and corrosion and stress corrosion cracking. The
text either presents the requisite backgroundfor each of these topics, or provides
referencesofothersourceswheregoodtreatmentscanbefound.
This book should also be useful to researchers who would like to learn more
aboutthe subject,or who wouldlike a more completeandintegratedtreatmentof
thetopicsthancanbefoundinindividualpapersonthesubject.Whilethechapters
areintegratedwithoneanotherandeachchapterbuildsuponthesumoftheprevious
chapters,itispossibletoreadselectedchaptersforjustthattopic.
As a final comment, the author would like to note that this book was written
bysorting,organizingandcondensinginformationfromseveraltextsandnumerous
journalandconferencepapersin ordertoarriveata comprehensivedescriptionof
the processes constituting radiationmaterials science. A conscientiouseffortwas
madetoacknowledgeandgivecredittotheoriginalsourcesoftheideas,theories,
mathematical developments and drawings contained herein. For occasional over-
sightsthatmayhaveoccurredduringthecondensationprocess,theauthoroffershis
apologies.Heisindebtedtothemanyauthorsandpublisherswhoprovidedmaterial
andillustrationsforthistext.
Finally, the author wishes to acknowledge the many colleagues, students and
friends who aided and advised him in this work. In particular, special thanks go
to Jeremy Busby, Todd Allen, Michael Atzmon, Roger Stoller, Yuri Osetsky, Ian
Robertson and Brian Wirth, for their substantive contributions to the content, to
Elaine West, Brian Wagner and Sean Lemecha for their work on the illustrations,
toCherilynDavisandOvidiuToaderfortheirhelpinmanuscriptandmovieprepa-
ration, to Lynn Rehn, Don Olander,Arthur Motta, Michael Nastasi, Steve Zinkle,
K. LingaMurty,LouMansurandPeter Andresenfortheirchapterreviews,andto
JohnKingandArdenBementforprovidingtheinspirationtotheauthortopursue
thisfieldmanyyearsago.
AnnArbor,May2007 GaryS.Was
Introduction
Radiation materials science describes the interaction of radiation with matter—
abroadsubjectcoveringmanyformsofirradiationandofmatter.Someofthemost
profoundeffectsof irradiationon materialsoccurin the core of nuclearpowerre-
actorswhere atomscomprisingthe structuralcomponentsare displaced numerous
times over the course of their engineering lifetimes. The consequences of radia-
tiontocorecomponentsincludeschangesinshapeandvolumebytensofpercent,
increasesinhardnessbyfactorsoffiveormore,severereductioninductilityandin-
creasedembrittlement,andsusceptibilitytoenvironmentallyinducedcracking.For
these structures to fulfill their purpose, a firm understandingof the effect of radi-
ation on materials is required in order to account for irradiation effects in design,
to mitigate its effect by changing operating conditions, or to serve as a guide for
creatingnew,moreradiation-tolerantmaterialsthatcanbetterservetheirpurpose.
The attractivenessof nuclear power as a presentday and futureenergysource
isduetothevastimprovementsthathavebeenmadeinthewayreactorsareoper-
ated andin our understandingof how these engineeringsystems degradeand fail.
Buttheattractivenessofnuclearpowerisalsodrivenbynewconceptsforadvanced
reactorsthatofferimprovementsinsafetyandreliability,radioactivewasteproduc-
tion,energyefficiencyandcosteffectiveness.Nuclearpowerholdsthepromisefor
producinghydrogeninacleanandlowcostprocessthatwouldpowerafuturehy-
drogeneconomy.Yetalloftheseimprovementscomeatacost.Thatcostisagreater
demandonthematerialsusedtobuildandoperatethesereactors.Newconceptsthat
promise better performancefrom this energy source also include more aggressive
environments,highertemperaturesandgreaterlevelsofirradiation.Inhisarticlein
Nature,Butler[1]summarizesthechallengesfacingseveralpromisingadvancedre-
actorconcepts.Inallbutone,materialbehavioristheleadingchallengeinbridging
thegapfromconcepttoreality.Thepivotalroleofmaterialbehaviorintheunique
radiation environmentcreated in a reactor core makes radiation materials science
of paramount importance in the future of nuclear energy in the world. It is with
this perspectivethat the objectiveof this text was formulated,to providea sound,
fundamentalunderstandingofradiationeffectsinstructuralmaterials.
Structural materials in reactor systems are predominantly crystalline, metallic
alloys.Virtuallyallofthestructuralmaterialsinreactorsaremetallic,andmanyof
thematerialsproposedforthemoreaggressiveconditionsinadvancedreactorcon-
cepts are metals as well. The types of radiation that can alter structural materials
X Introduction
consistofneutrons,ions,electronsandgammarays.Alloftheseformsofradiation
have the capability to displace atoms from their lattice sites, which is the funda-
mental process that drives the changes in structural metals described earlier. The
inclusionofionsamongtheirradiatingparticlesprovidesatie-intootherfieldsand
disciplines such as the use of accelerators for the transmutation of nuclear waste,
or in the creation of new materialsby ion implantation,ion beam mixing, plasma
assistedionimplantationandionbeamassisteddeposition.Alloftheconceptsde-
veloped in this text for the interactions of ions with solids are applicable to these
fieldsaswell.
The effectof irradiationon materialsis rooted in the initial eventin which an
energeticprojectilestrikesa target.While theevent ismadeup ofseveralstepsor
processes,theprimaryresultisthedisplacementofanatomfromitslatticesite.This
book will address primarily crystalline solids in which the atom locations are de-
finedbythecrystallinestructure.Irradiationdisplacesanatomfromitssite,leaving
avacantsitebehind(avacancy)andthedisplacedatomeventuallycomestorestin
alocationthatisbetweenlatticesites,becominganinterstitialatom.Thevacancy-
interstitial pair is central to radiation effects in crystalline solids and is known as
aFrenkelpair(FP).ThepresenceoftheFrenkelpairandotherconsequencesofir-
radiationdamagedeterminethephysicaleffects,andwiththeapplicationofstress,
themechanicaleffectsofirradiation.
The radiation damage event, detailed in Chap. 1, is concluded when the dis-
placedatom(alsoknownastheprimaryknock-onatom,PKA)comestorestinthe
latticeasaninterstitial.Thiseventconsumesabout10−11s.Subsequenteventsare
classifiedasphysicaleffectsofirradiation.Theseeffectsincludesuchphenomenaas
swelling,growth,phasechange,segregation,etc.Forexample,itispossibletotake
a blockofpurenickel, 1cmon a side, irradiateit in a reactor(to a fluence ofsay,
1022n/cm2) andmeasureitto be1.06cmona side,representinga volumechange
of20%!Thevolumechange,orswelling,isisotropicandisduetotheformationof
voidsinthesolid(seeforexample,Fig.8.1).
Anotherexampleisirradiationgrowth.Onecanirradiateacylindricalrodofura-
nium,10cminlengthand1cmindiameter(7.85cm3)toafluenceof∼1020n/cm2
and measure it to be 30cm in length and 0.58cm in diameter. The volume is un-
changed(7.85cm3),buttheshapeishighlydistorted.Distortionatconstantvolume
underirradiationisreferredtoasgrowth.
Phasechangesunderirradiationarealsocommon.ANi–12.8at%Al,solidsolu-
tionalloyirradiatedwith5MeVNi+ ionsto1016cm−2 willresultintheformation
ofaNi Alphase,whichisseparateanddistinctfromtheparentphase(seeforexam-
3
ple,Fig.9.3).Theformationofanewphaseisknownasirradiation-inducedphase
formationandisofgreatsignificanceinbothionandneutronirradiations.
Alastexampleofphysicalchangesofirradiationissegregation.IfaNi–1at%Si
+ ◦
alloyisbombardedwithNi ionsat525 Candto adoseofonedisplacementper
atom, the result is an enrichment of Si on the surface and at grain boundaries to
values that are 20 to 60 times the amount in the bulk (see for example, Fig. 6.5).
This redistribution of alloying elements to specific sites in the microstructure is
Introduction XI
knownasradiation-inducedsegregationandoccursinmanyalloysto a significant
extentwhenirradiatedathightemperatures.
Irradiation-inducedphysicalchangescanindeedbedramatic.Buthowdothey
alterthestructuralintegrityofcomponents?Thisistherealmofmechanicaleffects
of irradiation. Mechanical effects manifest themselves only under the application
ofastress.Theresultisthatalloysbehavemuchdifferentlythantheirunirradiated
counterparts.Forexample,theimpactenergyofanirradiatedsteelcanbedrastically
reduced.Forunirradiatedsteels,theenergyabsorbedisastrongfunctionoftemper-
ature, where at low temperatures, little energy is absorbed and the steel becomes
very brittle, butwith increasingtemperature,the energyabsorbingcapacity of the
steelincreasesdramatically.Irradiationofasteelwithneutronscancauseamarked
reductionin the strain and a several-foldincrease in the strength of the steel. The
resultisanincreaseinstrengthbyafactoroffiveandadecreaseinductilitybyover
afactoroften.Irradiationcanalsoinfluencethewayinwhichmaterialsdeformat
high temperature.Under a constant load, there is almost a complete loss of creep
strengthduetosevereembrittlementarisingfromirradiation.
Finally,irradiationtoaneutronfluenceof>5×1020n/cm2(E>1MeV)results
in accelerated intergranular cracking of iron- and nickel-base austenitic alloys in
light water reactors. This crackingphenomenonis verypervasivein that it affects
mostallausteniticalloysinalltypesofwaterreactors.Clearly,anyoftheseeffects
will have profound consequences on reactor component integrity. Understanding
howtheyworkisthekeytodesigningaroundtheirdetrimentaleffectsortodevel-
opingnewalloysthataremoreradiationtolerant.Asitturnsout,almostallofthese
effectshaveacommonlink:defectssuchasisolatedvacanciesandinterstitials,clus-
tersofvacanciesandinterstitials,dislocationloopsandlinesandvoidsandbubbles.
The readershouldkeep these defecttypesin mindas we movefromthe radiation
damageeventthroughthephysicaleffectstothemechanicaleffects.
We will addressthe radiation damageeventfirst as this is the basis for under-
standingalleffectsofirradiation.Wewillstartbyquantifyingtheextentofradiation
damageanddevelopaphysicaldescriptionoftheinteractionprocess.Inquantifying
the displacementprocess, what we are seeking is a quantitativedescription of the
number of vacancies and interstitials produced by an incoming projectile. Unless
we can do this, we have no hope of understandingthe extent of the damage. The
importanceofdeterminingtheeffectofirradiationintermsoftheproductionofde-
fects is discussed in Chaps. 2 and 3, and is shown here with a simple illustration.
Thenumberofdisplacementscreatedbyaneutronfluxisacomplicatedfunctionof
theenergydependenceofthatflux.NoteinthetopgraphinFig.I.1thatthedepen-
dence of the yield strength of a 316 stainless steel alloy on the neutron fluence is
highlydependentontheparticularneutronfluxspectrum[2].OWRisatestreactor
withatypicalLWRneutronspectrum,RTNS-IIproducedapure14MeVsourceof
neutrons and LASREF had a broad spectrum of high neutron energies. However,
if the yield strength is plottedas a functionof the displacementdamage in the al-
loy (dpa = displacementsper atom in the solid), then data from all three neutron
sourcescollapsesbeautifullyontoasingletrendline(bottomgraphinFig.I.1)that