Table Of ContentMaher I. Boulos
Pierre L. Fauchais
Joachim V.R. Heberlein
Thermal Spray
Fundamentals
From Powder to Part
Second Edition
Thermal Spray Fundamentals
Maher I. Boulos (cid:129) Pierre L. Fauchais (cid:129)
Joachim V. R. Heberlein
Thermal Spray Fundamentals
From Powder to Part
Second Edition
MaherI.Boulos PierreL.Fauchais
Départementdegéniechimiqueet SciencesdesProcédésCéramiqueset
degeniebiotechnologique deTraitementsdeSurface(SPCTS)
UniversitédeSherbrooke UniversitédeLimoges
Sherbrooke,QC,Canada LIMOGES,France
JoachimV.R.Heberlein(deceased)
DepartmentofMechanicalEngineering
UniversityofMinnesota
Minneapolis,MN,USA
ISBN978-3-030-70671-5 ISBN978-3-030-70672-2 (eBook)
https://doi.org/10.1007/978-3-030-70672-2
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Foreword
Thermalsprayingwasinventedandappliedforthefirsttimeclosetoacenturyago.In1909,the
Swiss engineer Max Ulrich Schoop got a first patent for the application of lead and zinc as
protectivecoatings.Initially,heusedacombustionprocessasaheatsourceformeltingofmetal
wires.Ahighvelocityflowofairorinertgasservedtoatomizetheliquefiedmetalandtopropel
theformeddropletstowardthesubstrate,whereitsolidifiedasalayer.Lateron,healsousedan
electricalarcforthispurpose.
These inventions represent, in principle, the beginning of the flame and wire arc spray
technology.Overthefollowingdecades,thermalsprayingevolvedintermsofbothtechnology
andthegreatvarietyofthematerialsthatcouldbesprayed.Thedrivingforcehasbeenmostly
economical since it offered means of modifying surface properties of parts and components
whereonlythesurfacehastobemadeofexpensivematerials.Duetotherelativelylowprocess
temperatureofflamespraying,theselectionofmaterialswhichcouldbeprocessedatthattime
was limited and hence the variety of producible coatings and intended applications. In the
middle of the last century, the need for coatings with materials of higher quality and melting
temperature increased notably and with the development of the first plasma spray torches in
mid-1950sbyThermalDynamicsCorporation,Metco,andPlasmadyne.Thesedevicesallowed
for the generation of considerably higher process temperatures, which in turn extended the
rangeofmaterialsandapplicationsthatcouldbecoated,andimprovedtheoverallqualityand
economicsoftheproducts.
Thestringentrequirementsoftheaerospaceindustrywerestrongtechnologydriversatthese
times.Basedonthefirstplasmatorchdesigns,newspraydeviceshavebeendevelopedwhich
continued up to now. For instance, besides the standard torches with plasma generation by a
direct current (DC) arcs struck between two electrodes, electrodeless devices such as induc-
tivelycouplingradiofrequency(RF)plasmatorcheshavebeendevelopedandareincreasingly
used for powder processing and the deposition of near net-shaped parts. Several process
modifications also cameinto application,suchasplasma sprayinginvacuumorlowpressure
(VPS)orcontrolledatmosphericspraying.Also,inthelowertemperaturerangeimprovements
and new processes could be attained, like spraying with high velocity flames (HVOF and
HVAF)andeventuallytheso-called“ColdSpraying.”Concerningtheprecursormaterials,the
spectrumincreasedconsiderably.Inadditiontotheconventionalwiresandpowdersofmetals,
ceramics,andpolymers,suspensionsandliquidscannowbeusedbynewsprayingmethods.In
particular, with suspension spraying, the grain size of powders suitable for processing can be
extended into the sub-micron range, for nanostructured coatings, giving rise to considerable
improvementofcoatingqualities.
Withthesenewprocessmodificationsandtheenlargedspectrumofprecursormaterials,the
variety of coatings and their industrial applications increased to an impressive extent. New
surface qualities and interesting combinations of substrate and surface properties could be
made, which otherwise were not possible, at least notwithacceptable price and effort. These
includecoatingsforprotectionagainstcorrosionorwear,forelectricalorthermalinsulation,for
highmechanicalstabilityandhardness,andforspecificelectrical,optical,electrochemical,or
catalyticproperties,whichcouldnowbeproducedonanindustrialscale.
v
vi Foreword
A main precondition for improving quality, economy, and reproducibility, and for the
acceptance in new application fields, was the need to gain a fundamental knowledge about
thebasicphysicsofthewholeprocesschainconcerning:
(cid:129) Theinteractionofthedepositionmaterialwiththeheatsource
(cid:129) Thetransientmeltingandacceleratingphaseofthematerial
(cid:129) Theinteractionwiththesurroundingatmosphere
(cid:129) Thematerialdeposition,wheresurfaceconditionsofthesubstratehasacriticalimpactonthe
resultingcoatingquality
Initsearlystages,thermalsprayingcouldbeconsideredasan“art,”whereempiricismand
experiencetogetherwitha“hothand”oftheoperatorforselectingtherightsetofthenumerous
process parameters guaranteed the success. Over the past three decades, thermal spraying
evolved into a mature science. This important step was greatly helped by improved fast
diagnosticsmethods,mainlybasedonlasersandcomputersandtheuseofnumericalmodeling
forthepredictionoftheinfluenceofthedifferentprocessparametersonthecoatingqualityand
itsperformance.
The three authors, leading international scientists in the field of thermal spray, have
presented in this book a large volume of knowledge and experience gathered over many
years of successful research and development work. This book is by far one of the most
comprehensive reviews of the state of the art in this field. As indicated in its title, it covers
the field of thermal spray from the powder all the way to the final part. On the one hand, a
systematicsurveyisgivenofthedifferenttypesofpowersourcesandprocesscharacteristicsin
thermal spraying for a large spectrum of applications, together with information about the
necessarycomponentslikematerials,equipment,controlunits,andapplieddiagnosticmethods.
Ontheotherhand,theanalysisofprocessfundamentalsisnotrestrictedtoaphenomenological
description, but is supported by extended theoretical considerations to understand the basic
phenomena involved behind the whole processes. Separate chapters are also devoted to
feedstockpreparation,whetherintheformofpowders,wires,cords,orrods,surfaceprepara-
tion, coating formation and characterization, online diagnostics and control, process integra-
tion, and industrial applications. An impressive number of figures and extensive list of
referencesfacilitateconsiderablytheunderstandingofthematerialandallowforgoingfurther
intodetails,whenevernecessary.
This impressive book is addressed to newcomers in the field of thermal spray as well as
experiencedresearchersandengineerswantingtoknowmoreaboutthescientificdetails,either
toimprovethequalityoftheirownproducts,andoftheirprocessefficiency,ortohaveguidance
inadecisionphase,whennewapplicationsorprocessesforincreasingtheproductportfolioare
thegoal.
Dr.Ing.RudolfHenne
RetiredfromGermanAerospaceEstablishment(DLR)
InstituteofTechnicalThermodynamics
Stuttgart,Germany
Preface
Following the publication of our first edition of this textbook and based on the very position
receptionitreceivedfromthegeneralscientificcommunity,theneedtokeepitupdatedinthis
rapidly developing field became increasingly obvious. Moreover, as we used the book on a
regular basis, we realized that with such a broad coverage of the field, certain improvements
couldbemadeinitsoverallstructuretomakeitmore“‘readerfriendly”andfacilitateitsuseas
(cid:129) Textbookforteachingpurposesatthegraduateschoollevel
(cid:129) Referencebookbyresearchscientistsintheirpursuitoffurtherdevelopmentsinthisfieldby
providingaccesstoahugevolumeofscientificliterature
(cid:129) Manualforpracticingengineersforthepurposeofsystemorprocessdesignthathopefully
would help in the understanding of some of the basic concepts behind thermal spray
technologies
Oneofthemainchangesmadeinthiseditionisthesubdivisionofthematerialpresentedinto
fourdistinctparts.
Part I,Basic Concepts, Chaps. 1,2, 3, 4and 5,isdedicated toareviewof thermal spray
coating and its position in the broader field of surface modification technologies. While not
being a textbook on combustion science or thermal plasma fundamentals, a brief review is
presentedonbasicconceptsinthesetwofields.Consideringthatalargepartofthermalspray
technologies is based on the in-flight heating and melting particles as they are injected into a
hot, combustion, or plasma spray stream, the material covering plasma or combustion
gas/particle momentum and heat transfer has been split into two chapters. One dealing with
basic transport phenomena taking place, in-flight, between a hot fluid stream and a single
particle. The following chapter is dedicated to a discussion of gas and particle dynamics in
thermal spray processes including the important concept of gas-particle interactions under
denseloadingconditions.
PartII,ThermalSprayTechnologies,Chaps.6,7,8,9,10,11and12,isdedicatedtothe
descriptionofadvances made ineachofthethermalspray technologiesincluding cold spray,
which,whilestrictlynotathermalsprayprocess,iswellpositionedinthisfieldandusedina
number of important applications. One change made in this group of technologies is the
splittingofthechapteronDCplasmasprayingintotworeasonablysizedchapters,onedealing
withDCplasmasprayingfundamentalsandtheotherwithDCplasmaprocesstechnologies.
Part III, Coating Formation and Characterization, Chaps. 13, 14, 15, 16 and 17, is
dedicated to the presentation of some of the broad topics in this field, including the
characteristics and main manufacturing routes of powders, wires, and cords as feed material
for different thermal spray processes. Surface preparation and coating formation through the
layering of successive splats are covered in the following three chapters. Special attention is
given tothe area ofnano-crystalline and nano-structured coatings and thegrowing interest in
thefieldofsolutionandsuspensionplasmaspraying.Anoverviewofbasiccoatingcharacteri-
zation techniques is discussed in a separate chapter in this part without attempting to be a
referencebookinthisfield,whichiswidelycoveredinthematerialscienceliterature.
Part IV, Process Integration and Industrial Applications, Chaps. 18 and 19, has also
been restructured with the chapter on process diagnostics and online monitoring and control
vii
viii Preface
integratedintothechapteronprocessintegrationandcontroltoavoidanyduplicationduetothe
importanceofinstrumentationandcontrolinmodernthermalsprayprocesses.Thischapteris
also expanded by introducing a wider range of examples of “spray booth” designs commer-
ciallyavailableinthefield.Thelastchapterofthisbook,dedicatedtoindustrialapplicationsof
thermal spray technologies, was revamped, including a comparative analysis of different
thermalsprayprocesses,whichcanbehelpfulinselectingtheappropriateprocessforagiven
application.Thisisfollowedbyareviewofthermalsprayprocessapplicationsgroupedinterms
ofeither“itsprocessobjectives,”oritsareaofuse“byindustry”orby“country.”Aswithour
lastedition,abriefeconomicanalysisispresentedattheendofthischapterwithoutattempting
either to cover this topic in an exhaustive fashion, being already the subject of numerous
textbooksdedicatedtoeconomicanalysisinthechemicalprocessindustries.
Suchanin-depthrevisionofthistextbookwasnotaneasytask,requiringhundredsofhours
ofhardworkwhichthankstoCOVID-19,wasinvoluntarilyavailabletousovertheyear2020.
The task was not simplified either by the death of our dear colleague Professor Joachim
V.R. Heberlein, who passed away in February 2014. His memory is cherished by us and
manyofhisfriendsandcolleaguesinthisfieldforhisvaluablecontributiontothefirsteditionof
thisbook.WewouldliketothankourlifepartnersAliceBoulosandPauletteFauchaisfortheir
continuedsupportandencouragement,withoutwhichthisformidabletaskwouldnothavebeen
possible.
Sherbrooke,QC,Canada MaherI.Boulos
Limoges,France PierreL.Fauchais
Preface (First Edition)
Thisbookisbasedonaseriesofcontinuingeducationcourseswhichhavebeenofferedbythe
authorsacrosstheworldinconjunctionwiththeInternationalSymposiumonPlasmaChemis-
try (ISPC) aspart ofits summer school overtheperiod1995–2011.Asimilarcourse,though
moreorientedtowardthermalspraytechnology,wasalsoofferedbytheauthorsinconjunction
withASMInternationalThermalSprayConferences(ITSC)overtheperiod1998–2010.Both
courses were offered to graduate students, practicing engineers, and researchers actively
involved in the field of thermal plasmas. Their emphasis was on the fundamentals behind
plasma processing and thermal spray technology, and the aim was to provide a grassroots
understandingofthebasicphenomenainvolved,necessaryfortakingthetechnologyoverthe
crucial step from being an “art” based on operator talent and experience to a mature science
withquantitativepredictivecapabilities.
This step did not come easily and without the intense involvement of many leading
researchersinthisfieldacrosstheworld.Thethreedeterminingfactorswhichwereofcritical
importancetotheevolutionofthisfieldoverthepastthreedecadesareasfollows:
(cid:129) Majorimprovementinprocessdiagnosticsandonlinecontrols
(cid:129) Thefastandsignificantdevelopmentofnumericalmodelingandcomputingcapabilities
(cid:129) Majordevelopmentinmaterialsscienceandmaterialscharacterizationtechniques
Intheprocessofpreparationofthemanuscriptforthisbook,whichspansmanyyears,the
authorswereconfrontedwiththecriticalneedtostrikeagoodbalancebetweentheneedtobe
conciseintheoverallpresentationofthesubjectandbeinginclusiveinstressingthefundaments
without overlooking the important applications which were the economical driver of the
technology. New technologies were also developed over this period which, while not being
“plasmatechnologies,”wererelevanttotheoverallfieldofsurfacetreatmentandcoating.These
were accordingly included in the book such as the combustion-based technologies and “cold
spray.”
We have no pretensions about having covered every aspect of this technology or exhaus-
tively reported on every relevant publication in this field. Exhaustive lists of references are
given at the end of each chapter. For those who were not cited, our apologies, it was not
intentional.Abookofthissizeandscopecouldnothavebeenpossiblewithouttheextensive
helpofstudents,researchassistants,colleagues,andassociates.Oursincerethankstoallwho
have helped make this book a reality. Particular thanks are due to Dr. Rudolf Henne who so
generously gave his time in the process of reviewing the manuscript of the book in its final
preparationstage.Wealsoappreciatehiswillingnesstowritetheforewordforthisbookwhich
reflectshislongandbroadexperienceinthefieldofthermalspray.Thefinancialassistanceof
thenumerousgovernmentandprivatefundingagenciesandindustrialpartnerswhohavealso
ix
x Preface(FirstEdition)
supported the basic and applied research behind this technology in our respective research
laboratoriesisgratefullyacknowledged.Oursincerethankstoourrespectivefamiliesandlife
partners,PauletteFauchais,YukoHeberlein,andAliceBouloswhohadtocopewiththelong
hoursofintensepersonaleffortsthatwereneededtocompletethisbook.
Limoges,France PierreL.Fauchais
Minneapolis,MN,USA JoachimV.R.Heberlein
Sherbrooke,QC,Canada MaherI.Boulos
