cold spray coating aimed at nanocrystallization

186 Pages·2011·40.64 MB·English

by  Ramin Ghelichi

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POLITECNICODIMILANO
MECHANICALENGINEERINGDEPRTMENT
DOCTORALPROGRAMMEINMECHANICALENGINEERING
COLD SPRAY COATING AIMED AT NANOCRYSTALLIZATION:
PROCESS CHARACTERIZATION AND FATIGUE STRENGTH
ASSESSMENT
DoctoralDissertationof:
RaminGhelichi
Supervisor:
Prof.MarioGuagliano
Tutor:
Prof.MarcoBoniardi
Coordinator:
Prof.GianpieroMastinu
Year2011-CycleXXIV
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Dedication
Tomylovelyparents
PashootanandFatemehGhelichi
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Acknowledgement
Itisamyththatadissertationisthesoul-wrenchingcreationsolelyofitsauthor’stime,toilandtenacity.
The current thesis is the product of contribution of the people who have been helping me sparingly
through these years. Although I am not able to appreciate completely and even mention the value of
theirsupport.
Iamdeeplythankfultomysupervisor,Prof. MarioGuaglianoforhisguidanceandinfinitesupport
ineverysinglestepofthisresearch. Hisintelligence,knowledge,andwisecommentshavealwayslitup
newwaysandideas. Nooneshouldbesubjectedtothetortureofreadingmyearlyattemptsattechnical
writing,andthankstoMario,noonewill. Hehelpedindifferentaspectsofmylifeduringtheyearsfar
fromhomeandkindlytreatedmelikeamemberofhisfamily.
It is difficult to overstate my gratitude to Prof. Hamid Jahed from University of Waterloo, who I
attributethelevelofmyMaster’sdegreetohisencouragementandefforts;withouthim,too,thisthesis
wouldnothavebeencompleted.
I owe my sincere gratitude to Prof. Bertrand Jodoin from University of Ottawa. It was an honor
toworkwithhisgroupMathieuBolducJean-LouisPelletier,Jean-MichelRoy,JamilAssad,Rubén
FernándezUrrutia,andespeciallyDanielMacDonald;withouttheirsupportandfriendlyhelpsIwould
notabletogetthisthesisdone.
I thank Prof. Ines Inés Fernández Pariente from University of Oviedo, for her kind-great efforts
andfriendlysupportwhichgaveuntiringhelpduringdifficultmoments.
MygreatappreciationtoProf.MarcoVeranifromMathematicsDepartment,forhelpingmethrough
mathematicalapproaches; hisintelligencealongwithinspirationhasopenednewdoorsformeandhas
hadaremarkableinfluenceonmyentireresearch.
My sincere thanks to Prof. Laura Vergani, Prof. Gianpiero Mastinu, Prof. Bianca Maria
Colosimo and especially Prof. Andrea Bernasconi for their detailed review, constructive criticism
andexcellentadvicesduringthepreparationofthisthesis.
AspecialmentionshouldbemadeofthestaffsofC4,CLASDandOrigoniBLabs,whohavebeen
veryhelpfulwithexperimentalset-upsandpracticaladvices:LuigiLanzani,MauroDeMori,Luciano
Lucherini,FilippoSpinelli,AndreaDelViscio,SergioBruno,MorenoRiccardi,GiuseppeGhilardi,
Marco Ghilardi, Dario Giusti, Pasquale Aquilino, Francesco Cacciatore and Maurizio Pardi; in
particularAlessandroTosiandMaurizioGroppiwhoreadilytooktimeoutoftheirbusyschedulesto
help me frequently with all the experimental tests and machines. Pietro Pellin and Maurizio Pardi
deservespecialthanksfortheirhelpthroughtheXRDmeasurements,microscopysamplepreparations,
etc. IwishtothankLucaSignorelliforhiscontributionsoftime,ideasandexperiences.
I would like to express my gratitude to Dr. Simone Vezzù from Nanofab Lab. in Civen for his
generoussupportandexecutionofcoatingonourspecimens.
IhavetoappreciatetheworkofmydearfriendsAntonioMairanoandDanieleVagowhoastheir
Masterthesishavecontributedtothisresearch.
Thesupportandcareofmyfriendshelpedmeovercomesetbacksandstayfocusedonmygraduate
study. I greatly value their friendship and I deeply appreciate their belief in me: Francesco Benzoni,
Dr. KhaydarValiullin,Dr. ChiaraColombo,FlaviaLibonati,Dr. MauroMadia,LucaPatriarca,
Ermes Tarallo, Gabriella Tarantino, Augusto Sciuccati, Dr. Yonatan Afework Tesfahunegn, and
ElisaMarchesin.InparticularIowemydeepestgratitudetoMassimoFossati,DavideCrivelli,Giorgo
Vallone, andespeciallyDr. EdoardoConradowhohavebeenalwaysreadytolendahandandassist
witheverytypeofproblems.
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IamgratefultoFrancescaMassaro,LilianaMusazzi,AlessandraMiceliandespeciallyCaterina
BarbieriforteachingmeItalianlanguage. Theirkindeffortthroughtheseyearsisunforgettable.
It is necessary to mention and thank the kind hospitality and support of Dr. Amin Eshraghi, Dr.
MorvaridKarimiGhovanlou,Dr. MohammadrezaNoban,andHassanMahmoudiduringmystay
inCanadawhichmadeeverythingsimplertome.
IamgratefultotheDepartmentSecretary, LiciaSimonelliforhervariousformsofsupportduring
mygraduatestudy.
The financial support of Politecnico di Milano and Scuola Interpolitecnica which gave me the
opportunityandencouragementtoexpandmyresearches,isgratefullyacknowledged.
IowemylovingthankstoDr. SaraBagherifard. Herdedication,constantencouragement,sparing
assistance,andsupporthavealwaysbeentrulyvaluable.
Lastbutnotleast,IwishIwasabletothankmylovelyfamily.IamgratefultomyparentsPashootan
andFatemehGhelichi,wholovedmewithinfinitegenerosityandprovidedmewiththeopportunityto
bewhereIam. Withoutthem,noneofthiswouldevenbepossible.
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Abstract
T
HE everincreasingresearchoflightness,improvedperformance,safetyandreliabilityispushing
tolookformaterialswithsuperiormechanicalpropertiesandtomeetseveredesignrequirements
imposedinmanyfieldsofapplication,inordertoobtaincompetitiveproducts.Nanocrystal(NC)
materials are experiencing a rapid development in recent years due to their existing and potential ap-
plications in a wide variety of technological areas; thanks to their superior mechanical properties that
by some means are different from their conventional coarse grained polycrystalline counterparts. The
commercialapplicationsofnanomaterials, beyondtheboundariesoflaboratories, lieonthesuccessful
production and consolidation of these materials into components preserving the nanostructures. Cold
Spray(CS)coatingisaninnovativedepositiontechniquewhichuseselementsofbothphysicaldeposi-
tionandsevereplasticdeformationforgeneratingNC.CSisanemergingcoatingprocessinwhich, in
contrasttootherwell-knownthermalsprayprocessessuchasflame,arc,andplasmaspraying,powders
do not melt before impacting the substrate. This character makes CS process commendable for many
different coating applications dealing with various materials not only metals but also polymers, com-
posites, etc. Bonding of particles to the substrate occurs due to the high kinetic energy upon impact;
therefore, the velocity of the particle plays the most important role in material deposition. During the
process,powdersareacceleratedbyinjectionintoahighvelocitystreamofgas.Thehighvelocitystream
isgeneratedthroughaconverging-divergingnozzle. Itiswellrecognizedthatparticlevelocitypriorto
impact is a key parameter in CS process. It determines what phenomenon occurs upon the impact of
sprayparticles,whetheritwouldbethedepositionoftheparticleortheerosionofthesubstrate. Critical
velocity(CV)foragivenpowderisdefinedasthevelocitythatanindividualparticlemustattaininor-
dertodepositafterimpactingthesubstrate. ExperimentalmeasurementoftheCVispracticallyalmost
impossibleduetothefactthatthewholedepositionprocessforasingleparticlelastslessthanfewnano
seconds. A finite element (FE) model using commercial Abaqus/Explicit has been developed in order
to simulate the phenomenon and broaden the horizon of the physical background of the process. The
generalagreementsupportstheideathatadiabaticshearinstabilityplaysanimportantroleinthebonding
of the particles. Having used a material model which considers softening phenomenon and strain rate
effect, CV, is numerically estimated by characterizing the shear instability that appears in the discrete
outputsofthesoftwareasasingularityintheirfunctions. Thesingularityhasbeenfoundbytransferring
theresultsinfrequencydomainusingWavelettransformandanalyzingthesmoothnessofthefunctionby
calculatingitssecondderivativeinSobolevspace.Theresultsfortestedmaterialshowagoodcorrespon-
dencewiththeexperimentalmeasurements. AnotherFEmodelhasbeendevelopedinordertoexamine
thepeeningeffectoftheparticlesonthesubstrate. particle’speeningeffect,inducesresidualstressand
high plastic deformation. The compressive residual stress generally increases the fatigue endurance of
structures;moreover,recrystallizationcanoccurasaresultofhighplasticdeformationofthespecimen’s
surface. In CS, particle diameters have a Rosin-Rammler distribution; their velocity and temperature
arefunctionsofparticlediameterbasedontheinitialconditionoftheprocess. Although,thenumerical
modelconsiderstherandomnessoftheparticlesinsizeandimpactpositionwiththeappropriatedistri-
butionandforeachparticle,basedonitssize,usesrelatedvelocityandtemperature,unfortunately,the
results of the numerical simulation, in case of residual stress assessment, are not in a good agreement
withtheexperimentalmeasurementperformedbyX-raydiffraction(XRD).Itmightbeduetothefact
thattheFEsimulationcannotmodelthebondingphenomenonwhichseemsveryimportantinthepro-
cess. TheFEsimulationpredictsthepossibilityofnanograingenerationonthesubstrateduetothefact
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II ABSTRACT
thattheequivalentplasticstraincausedbyparticles’impactismeasuredtobemorethanthethreshold
valuesuggestedbyscholarsasacriterionforgrainsizerefinement.Thegrainsizeofthecoatedsamples,
notonlyonthedepositedmaterialbutalsoonthesubstratebyremovingthedepositedmaterialusingan
electro-polishingdevice,hasbeenmeasuredthroughXRDmeasurements.Thein-situXRDtestmachine
hasbeenemployedtoextractthediffractionpeakswhichareusuallyusedforstressmeasurements.Voigt
formulationisappliedontheoutputoftheXRDdeviceinordertoseparatethegrainsizeandmicrostrain
dataandconsequentlymeasurethegrainsizeofthetreatedsamples. Theresultsapprovetheexistence
ofnanograinsonthesubstrate,aswasassessedalsobythenumericalsimulation. TheeffectofCScoat-
ing on fatigue strength of specimens coated by different powders has been studied using the specimen
design suggested by standard (ASTM593). A load control test machine which satisfies the perquisite
requirementsofthestandardhasbeendevelopedintheLabs. ofMechanicalEngineeringDepartment,
PolitecnicodiMilano; Themachinehasbeencalibratedusingstraingaugesandcheckingtheeffective
distanceandfrequencyonthespecimensunderdifferentloads. Inthisregard,sixaluminumalloyseries
havebeenpreparedwithdifferenttreatmentsusingdiversealuminumalloypowders. Theresultsofthe
purebendingfatiguetestsindicatethatCScoating,regardlessofthedepositedmaterialtype,increases
thefatiguestrengthofthetreatedspecimens. Depositingpowderswithhigherhardnesscomparedtothe
substrate, will improve the fatigue strength more than the softer powders. It is also observed that the
softerdeposition,insomecases,donotparticipatetotheloadbearingprocessduetopartialdelamina-
tionofthedepositedmaterialfromthesubstrate. Thelasttentative,hasbeentoproducenanostructures
through severe shot peening after application of CS coating. This combined process was expected to
resultinbenefitingfromadvantagesofbothcoatingandshotpeeningonthesamples. Inthiscase, the
fatiguestrengthdoesnotincreasewithrespecttothepreviousnotshotpeenedseries. Althoughthegrain
size on the samples after shot peening are measured to be less than 100 nm, due to the existence of
microcracksandseverelydeformedsurfaceofthesamplesthatactassurfacedefects,itisnotpossible
tobenefittheadvantagesofthegeneratedNCtoimprovefatiguestrength.
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Contents
I Introduction 1
1 IntroductiontoNano-crystallineMaterial 3
1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 MechanicalpropertiesofNCmaterial . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2.1 Elasticproperties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2.2 Hardnessandstrength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.2.3 Ductility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.2.4 Fatigueandfracture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.3 ProductionofNCstructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.3.1 Electrodeposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.3.2 Inert-gascondensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.3.3 Solidstateprocessingmethods . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.4 Measurementtechniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.4.1 Crystallography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.4.2 Microscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.5 ApplicationofNCmaterial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.5.1 Nanotechnologyinautomotiveapplications . . . . . . . . . . . . . . . . . . . . 14
1.5.2 Industrialapplicationsofnanocompositecoatings . . . . . . . . . . . . . . . . . 14
1.5.3 Biomechanicsandprosthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2 IntroductiontoColdSprayCoating 19
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.2 Coldspraycoatingprocess . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.2.1 Principalprocessparameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.3 Advantagesofcoldspraycoating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.4 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.4.1 Wearresistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.4.2 Corrosionprotection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.4.3 Repairofdamagedcomponents . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.4.4 CoatingandNC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.5 Effectofcoldspraycoatingonfatiguestrength . . . . . . . . . . . . . . . . . . . . . . 30
2.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3 ShotPeeningandSurfaceNano-crystallization 35
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.2 Shotpeeningcontrolparameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.2.1 Almenintensityandsaturationcurve . . . . . . . . . . . . . . . . . . . . . . . 37
3.2.2 Surfacecoverage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.3 Shotpeeningprocesstoobtainnano-structuredsurface. . . . . . . . . . . . . . . . . . . 38
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IV CONTENTS
3.4 Fatiguebehaviorofsurfacenanocrystallizedmaterialobtainedbyshotpeening . . . . . 39
3.5 Numericalsimulationofshotpeening . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
II Numericalsimulations 45
4 Criticalvelocitycalculation 47
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4.2 ExperimentalmeasurementofCV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.3 NumericalsimulationforCVassessment: areview . . . . . . . . . . . . . . . . . . . . 50
4.4 AnewapproachtofindtheCVbyFEM . . . . . . . . . . . . . . . . . . . . . . . . . . 52
4.4.1 FEMmodel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
4.4.2 Boundarycondition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
4.4.3 Materialmodel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4.4.4 Damagecontrol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
4.4.5 Adiabaticshearinstability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
4.4.6 Meshconvergencestudy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4.4.7 Challengesinfindingtheshearinstability . . . . . . . . . . . . . . . . . . . . . 57
4.4.8 DiscretenumbersandSobolevspace . . . . . . . . . . . . . . . . . . . . . . . . 57
4.4.9 Algorithmoftheprocess . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
4.4.10 DenoisingTechnique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
4.5 Evaluationofthenumericalmodel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
4.5.1 Particledeformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
4.5.2 ComparisonofCV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
4.6 EffectoftheprocessparametersonCV . . . . . . . . . . . . . . . . . . . . . . . . . . 67
4.6.1 Temperatureoftheparticles . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
4.6.2 EffectofShotpeeningbeforecoating . . . . . . . . . . . . . . . . . . . . . . . 69
4.7 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
5 Numericalassessmentofthecoatedsurface 75
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
5.2 IntroductiontotheFEMmodel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
5.2.1 Particlesize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
5.2.1.1 Singleshotmodel . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
5.2.1.2 Particlesizeconsiderations . . . . . . . . . . . . . . . . . . . . . . . 77
5.2.2 Particlevelocity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
5.2.2.1 Singleshotmodel . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
5.2.2.2 Particlevelocityconsiderations . . . . . . . . . . . . . . . . . . . . . 81
5.2.3 Particletemperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
5.2.3.1 Singleparticlemodel . . . . . . . . . . . . . . . . . . . . . . . . . . 83
5.2.3.2 Particletemperatureconsideration . . . . . . . . . . . . . . . . . . . 84
5.3 Numericalmodel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
5.3.1 Obtainingtheresults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
5.3.2 Processimplementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
5.4 Resultsofmulti-impactmodel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
5.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
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