High Temperature Oxidation and Corrosion of Metals

733 Pages·2016·55.564 MB·English

by  David John Young

High Temperature
Oxidation and
Corrosion of Metals
Second Edition
David J. Young
School of Materials Science and Engineering, University
of New South Wales, Sydney
AMSTERDAMlBOSTONlHEIDELBERGl LONDONlNEWYORKlOXFORD
PARISlSANDIEGOl SANFRANCISCOlSINGAPORElSYDNEYlTOKYO
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Coverimage:Burnerrigtestsinbothheatingandcoolingpositionsethermalbarriercoatedsuper
alloyhot.CourtesyoftheNationalAeronauticsandSpaceAdministration,JohnH.Glenn
ResearchCenteratLewisField(NASAIdentifierGRC-C-1999-2487).
Foreword
The depletion of the first edition print run and an enormous increase in pub-
lished research on high-temperature corrosion have combined to make a
second edition of this book desirable. Recent work on mass transport in
alumina and, more generally, on oxide grain boundary diffusion has contrib-
uted improved clarity to our understanding of how protective alumina and
chromiascalesbehave.Similarly,newinvestigationsintowatervapoureffects
on scaling processes have expanded and refined our knowledge, although a
simple, coherent picture remains elusive. These contributions, and several
others, have been drawn upon in updating the original text.
Two new topics have been added, reflecting the large body of published
research now available and the technological developments which drove that
work.Chapter10treatscorrosionbycarbondioxide,animportantissueifCO
2
is to be captured from combustion gas streams. In addition, the thermal
properties of carbon dioxide, along with its pressure-volume-temperature
characteristics,makeitattractiveasaheattransferandworkingfluid.Forthese
reasons, it is a candidate for use in nuclear reactors and concentrated solar
thermal power generation. Unfortunately, it is also corrosive to a variety of
alloys.
AnewChapter12,CorrosioninComplexEnvironments,isconcernedwith
the corrosion phenomena arising from the presence of ionic melts and vola-
tilising halides. Interest in these topics has arisen out of the much increased
use of both biomass and municipal waste as fuels for thermal power genera-
tion. The resulting flue gases and deposits can be remarkably corrosive, and
boiler operating temperatures are strictly limited as a result.
As in the first edition, I have tried to acknowledge important contributions
to our understanding made by many researchers, and I apologise for any
omissions.Thesecondeditionhasbenefitedfromcolleaguesaroundtheworld
who have offered hospitality and/or generously gave expert commentary:
Brian Gleeson (University of Pittsburgh), Daniel Monceau (INPT-CIRIMAT,
Toulouse), Bruce Pint (Oak Ridge National Laboratory), Joe Quadakkers
(Forschungszentrum, Ju¨lich), Michael Schutze (Dechema, Frankfurt) and Jim
Smialek (NASA, Lewis). Rectifying an important omission from the first edi-
tion,Ithankmywifeandfamilyfortheirsupportandremarkableforbearance.
David J. Young
December 2015
xiii
Preface
Almostallmetalsandalloysoftechnologicalinterestoxidiseandcorrodeathigh
temperatures. However, the nature of their reaction products and the rates at
whichmetalsurfacesaredegradedvarywidely,andacapacityforpredictionis
highlydesirable.Thisbookisconcernedwithprovidingafundamentalbasisfor
understanding the alloy-gas oxidation and corrosion reactions observed in
practiceandinthelaboratory.Itspurposeistoenablethepredictionofreaction
morphology,kineticsandrateasafunctionoftemperatureandthecomposition
ofbothalloyandgas.
The term ‘oxidation’ is used in a generic sense for any chemical reaction
which increases the metal oxidation state by forming a compound such as an
oxide,sulphide,carbide,etc.Alloy oxidationreactionscanbeconceived ofas
occurringinthreestages.Initially,allreactivecomponentsofanalloyincontact
with a hot gas are likely to react simultaneously. Subsequently, more thermo-
dynamically stable compounds replace less stable ones, and a state of near
equilibriumislocallyapproached.Thereactingsystemcanthenbemodelledasa
seriesofspatiallyadjacentlocalequilibriumstateswhichvaryincrementallyin
reactant chemical potentials. During this stage, the reaction morphology and
compositiondistributionareinvariantwithtime.Ultimately,this‘steadystate’is
lost,andallreactivealloycomponentsareconsumedinafinalbreakdownstage.
Successfulalloysarethosewhichevidencelengthyperiodsofslow,steady-
statereaction.Forthisreason,considerableemphasisisplacedonanalysingthe
underlyinglocalequilibriumconditionandtestingitsapplicabilitytoparticular
metaloralloy-oxidantsystems.Whenanalloy-gasreactionisatasteadystate,
the constant composition profile developed through the reaction zone can be
mappedontotherelevantsystemphasediagramasa‘diffusionpath’.Frequent
useismadeofthesepathsinunderstandingreactionproductdistributionsandin
predicting,oratleastrationalising,reactionoutcomes.
Analysis of the alloy oxidation problem requires a multidisciplinary
approach.Physicalmetallurgy,materialsscienceandphysicalchemistryprovide
the tools with which to dissect alloy phase constitutions and their trans-
formations, oxide properties and chemical kinetics. Deliberate emphasis is
placedontheuseofchemicalthermodynamicsinpredictingoxidationproducts
anddescribingsolidsolutionphases.Equalattentionispaidtothedetailedun-
derstandingofdefect-baseddiffusionprocessesincrystallinesolids.Theintro-
ductoryChapter1indicateshowthesevariousdisciplinescancontributetothe
xv
xvi Preface
analysis. The lengthy Chapter 2 reviews the thermodynamic, kinetic and
mechanicaltheoriesusedinthisbook.Italsocontainstabulateddataandrefers
toAppendicesonalloycompositionanddiffusion.
After these preliminaries, the book is arranged in a sequence of chapters
reflectingincreasingcomplexity,whichequateswithgreatersystemcomponent
multiplicity.Ananalysisofthereactionbetweenpuremetalsandsingleoxidant
gasesis followedby a discussion ofmetal reactionswith mixedoxidant gases
and then, in Chapters 5e7, an examination of alloy reactions with a single
oxidant. Much of this discussion is based on the early work of Carl Wagner,
whichstillprovidesagoodconceptualframeworkand,inseveralcases,auseful
analytical basis for quantitative prediction. However, as will be shown,
increasing system complexity is accompanied by a weakening in theoretical
completeness. The problems arise from multicomponent effects and from
microstructuralcomplexity.
Consider first the effect of increasing the number of alloy components. A
steady-statereactingsystemconsistingofabinaryalloyandasingleoxidantcan
be modelled in a two coordinate description of both thermodynamics and
diffusion kinetics, provided that temperature and pressure are constant. Sub-
stantialthermodynamicanddiffusiondata isavailable formanysuchsystems,
andthisisusedindevelopingdiffusionpathdescriptions.Increasingthenumber
of alloy components leads, however, to chemical and structural interactions
among them, rendering the experimental problem much less tractable, and
diagrammaticrepresentation impossible. In the absenceof the requisiteexten-
sive thermodynamic and diffusion data, the Wagner theory cannot be applied.
Instead, higher order alloys are discussed from the point of view of dilute
additioneffectsonthebehaviourofbinaries.
Wagner’s theory is based on lattice diffusion. However, the transport
properties of slow-growing oxides are largely determined by their grain
boundaries and, in some cases perhaps, microporosity. Additional alloy com-
ponentscanaffectboththeoxidegrainsizeandthediffusionpropertiesofthe
grain boundaries. A description of these phenomena is, at this stage, largely
empirical.
Thelatterpartofthebookisconcernedwiththeeffectsofothercorrodents
and temperature variations. Chapters 8 and 9 deal with sulphur and carbon-
bearing gases.Theveryrapiddiffusionrates involvedinsulphidationandcar-
burisationmakesthempotentiallythreateningcorrosionprocessesinanumber
ofindustrialtechnologies.Offundamentalinterestarethecomplicationsarising
outofthecomplexgas-phasechemistriesandthesometimesslowhomogeneous
gas-phasereactions.Itbecomesnecessaryindiscussingthebehaviourofthese
gasmixturestoconsidertheroleofcatalysts,includingthealloysinquestionand
theircorrosionproducts.Itemergesthatnotonlythegasphase,butalsothegas-
solidinterfacecanbefarremovedfromlocalequilibrium.Inparticular,analysis
of the catastrophic ‘metal dusting’ corrosion caused by carbon-supersaturated
gasescallsfortheuseofnonequilibriummodels.
Preface xvii
The effects of water vapour on oxidation are discussed in Chapter 10. In
many respects this is the least well understood aspect of high-temperature
corrosion. The reason for the difficulty is to be found in the multiple ways in
which water molecules can interact with oxides. Preferential adsorption,
hydrogen uptake, lattice defect changes, grain boundary transport property
changes, gas generation withinoxideporesandscale andscale-alloy interface
mechanicalpropertychangesneedalltobeconsidered.
Finally, the effects of temperature cycling on oxide scale growth are
considered in Chapter 11. A combination of diffusion modelling with a rather
empiricalscalespallationdescriptionisfoundtoprovideareasonablysuccessful
way of extrapolating data for particular alloys. However, there is a need for
developmentofmorepredictivedescriptionsoftherelationshipbetweenspall-
ationpropensity,alloypropertiesandexposureconditions.
Discussion is focused throughout on developing an understanding of the
fundamentals of high-temperature oxidation. Frequent use is made of experi-
mental informationon real alloysinorder toillustrate the principles involved.
However,noattemptismadetosurveytheveryextensiveliteraturewhichexists
for alloy oxidation. Thus most examples considered concern either iron- or
nickel-base alloys, whereas cobalt-base alloys are largely ignored. Nickel alu-
minidesarediscussed,butotherintermetallicsareseldommentioned.Thescope
of the book is further limited by the exclusion of some particular topics.
Examplesinclude‘pesting’(disintegrationbygrainboundaryattack)ofsilicides,
andextensiveoxygendissolutionbymetalssuchastitaniumandzirconium.No
bookofmanageableproportionscaneverbecomplete,orevenfullyuptodate.
Itisremarkablethatsincetheearly,verysubstantialprogressmadebyCarl
Wagner and associates in understanding oxidation phenomena, the research
effort has nonetheless continued to expand. The reason, of course, is the
continuing need to operate equipment at ever higher temperatures to achieve
greaterefficienciesandreducedemissions.Theneedtodevelopsuitablemate-
rialscanbeexpectedtodriveevenmoreresearchinyearstocome.
Writingthisbookhasbeenalargetask,anditscontentinevitablyreflectsmy
own experience, as well as the ideas and results of others. I have tried to
acknowledge important contributions to our understanding made by many
researchers,andapologiseforanyomissions.Myownresearchinthisareahas
benefited from interaction with many talented students, research fellows and
colleagues, all acknowledged bydirectreference. Ithasalsobeensustainedin
largepartbytheAustralianResearchCouncil,abodytobecommendedforits
willingness to support fundamental research. This book has benefited from
colleagues from around the world who offered hospitality and/or generously
gaveexpertcommentaryasIwrote:BrianGleeson(IowaStateUniversity),Jack
Kirkaldy (McMaster University), Daniel Monceau (CIRIMAT, Toulouse),
Toshio Narita (Hokkaido University), Joe Quadakkers (Forschungzentrum,
Julich),JimSmialek(NASA,Lewis)andPeterTortorelli(OakRidgeNational
Laboratory).
xviii Preface
Finally,Iacknowledgewithgratitudeandaffectiontheinspirationprovided
by my mentors and friends at McMaster University, Walt Smeltzer and Jack
Kirkaldy.
DavidJ.Young
August2007
Abbreviations and Acronyms
APT Atom probe tomography
CTGA Continuous thermogravimetric analysis
CVD Chemical vapour deposition
EBSD Electron back scattered diffraction
EDAX Energy dispersive analysis of X-rays
EELS Electron energy loss spectroscopy
EPMA Electron probe microanalysis
FIB Focused ion beam
IGCC Integrated gasification combined cycle
ppm Parts per million (unit of relative concentration)
ppma Parts per million by atoms
ppmm Parts per million by mass
PVD Physical vapour deposition
SAD Selected area diffraction
SCC Supercritical CO
2
SEM Secondary electron microscope
SIMS Secondary ion mass spectrometry
TBC Thermal barrier coating
TEM Transmission electron microscope
TGA Thermogravimetric analysis
TGO Thermally grown oxide
XPS X-ray photoelectron spectroscopy
XRD X-ray diffraction
YSZ Yttria-stabilized zirconia
xix
Symbols
GREEK SYMBOLS
a Coefficientofthermalexpansion
a Enrichmentfactorformetalininternaloxidationzone
d Thicknessofgasphaseboundarylayer
d Deviationfromstoichiometryinoxide
h Electrochemicalpotentialofcomponenti
i
h Viscosityofgas
g
g Surfacetension,freeenergyperunitsurfacearea
g Activitycoefficientofcomponenti
i
l Interplanardistance,jumpdistance
l x=t12,forparametricsolutionstoFick’sequation
m Chemicalpotentialofcomponenti
i
n Stoichiometriccoefficientinchemicalreactionorcompound
vg Kinematicviscosityofgas
n Kineticfrequencyterm
iv
vP Poisson’sratio
j Electrostaticpotential
r Density
s Mechanicalstress
q Fractionofsurfacesites
x Extentofreaction
x MolefractionofoxideBOinsolidsolutionA1(cid:1)xBxO
εc Criticalstrainformechanicalfailureofscaleorscale-alloyinterface
ε Wagnerinteractioncoefficientsforsolutecompoundsiandk
ik
ε Mechanicalstraininoxide
OX
SYMBOLS
A Surfaceareaofoxidisingmetal
ai Chemicalactivityofcomponenti
a0;a00 Boundaryvaluesofoxygenactivityatmetal-scaleandscale-gas
o o
interfaces
Bi Mobilityofspeciesi
Ci Concentrationofcomponenti
C0,C00 Boundaryvaluesofconcentrationatmetal-scaleandscale-gasinterfaces.
D Diffusioncoefficient
d Grainboundarywidth
DA IntrinsicdiffusioncoefficientforspeciesA
DA* Tracerorself-diffusioncoefficientofspeciesA
Dij Diffusioncoefficientrelatingfluxofcomponentitoconcentration
gradientincomponentj
xxi
xxii Symbols
e
D Chemical(orinter)diffusioncoefficient
Do Diffusioncoefficientforsoluteoxygeninalloy
Do,i Diffusioncoefficientforoxygenalonganinterface
E Electricfield
EOX Elasticmodulusofoxide
EA Activationenergy
e0 Freeelectron
F TheFaraday(96,500C)
f Fraction
fv Volumefraction
G TotalormolarGibbsfreeenergy
GOX Shearmodulusofoxide
Gv Freeenergyperunitvolume
gBO Volumefractionofinternallyprecipitatedoxide,BO
H Totalormolarenthalpy
hl Positivehole
ijS Speciesiadsorbed(bound)tosurfacesite
ioz Internaloxidationzone
Ji Fluxofcomponenti
K Chemicalequilibriumconstant
k Rateconstant
k Boltzmann’sconstant
kc Parabolicrateconstantformetalconsumption,corrosionrateconstant
kl Linearrateconstantforscalethickening
km Gaseousmasstransfercoefficient
ks Surfaceareafractionofoxidespalled
kðiÞ Parabolicrateconstantforinternaloxidation
p
kp Parabolicrateconstantforscalethickening
kw Parabolicrateconstantforscalingweightgain
kv Vaporisationrate
Kp Equilibriumconstantatfixedpressure
Ksp Solubilityproduct
KIC Fracturetoughness,criticalstressintensityfactor
Lij Generalmobilitycoefficient,Onsagerphenomenologicalcoefficient
L Lengthofmaterialoverwhichgasflows
l Halfthicknessofalloysheet
MW Molecularweight
mi Molarconcentrationofcomponenti
ml,m0 Numberofchargeunitsonlatticepointdefectspecies
n Numberofmoles
Ni Molefractionofcomponenti
NAV Avogadro’snumber
NM,i MolefractionofcomponentMatscale-alloyinterface
NM,min MinimummolefractionofcomponentMrequiredtosupportgrowthof
externalMOscale
NðoÞ MolefractionofcomponentMoriginallypresentinalloy
M
NðsÞ Molefractionofdissolvedoxygenatalloysurface
O
P Pressure
p DA/DB,ratioofmetalself-diffusioncoefficientsinternaryoxide
pi Partialpressureofcomponenti