A parametric study of Inconel 625 wire laser deposition

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ContentslistsavailableatScienceDirect

Journal

of

Materials

Processing

Technology

j o ur na l h o me p a g e :w w w . e l s e v i e r . c o m / l o c a t e / j m a t p r o t e c

A

parametric

study

of

Inconel

625 wire

laser

deposition

T.E.

Abioye,

J. Folkes,

A.T.

Clare

∗

ManufacturingDivision,FacultyofEngineering,UniversityofNottingham,NG72RD,UnitedKingdom

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received14February2013 Receivedinrevisedform1May2013 Accepted10June2013

Available online 20 June 2013 Keywords: Laser Deposition Inconel625 Wire Dilution Processcharacteristics

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Laserdepositionwithwireofferssavingpotentialsoverpowderbasedsystems.Theseincludeacleaner processingenvironment,reducedeconomicandenvironmentalcostofproducingthewire,better sur-facefinishandhighermaterialdepositionrates.Thistechniqueisrapidlyfindingapplicationsforthe manufactureandrepairofhighvaluecomponents.Forthefirsttime,thedepositionofInconel625wire forsingletracksatvaryingprocessingparametersusinga2-kWYtterbiumdopedfibrelaserhasbeen investigated.Aprocessmappredictingtheprocesscharacteristicsintermsofwiredripping,smooth wiretransferandwirestubbingatdifferentcladdingconditionshasbeendeveloped.Trackgeometrical characteristicsincludingaspectratioandcontactanglewereevaluatedusingsurfaceprofilometryand opticalmicroscopy.ScanningelectronmicroscopyequippedwithenergydispersiveX-rayspectroscopy wasusedtodeterminethedilutionratio(%)ofthetracks.Wiredepositionvolumeperunitlengthoftrack andenergyperunitlengthoftrackwerefoundtobekeyparametersinfluencingboththeprocessand trackgeometricalcharacteristics.Aspectratioanddilutionratioshowedpositivedependencywhereas contactangleshowednegativedependencyonenergyperunitlengthoftrack.Conversely,material depo-sitionvolumeperunitlengthoftrackvarieddirectlywithcontactanglebutinverselywithaspectratio anddilutionratio(rangingfrom0%to24%).Processingconditionsatwhichacombinationoffavourable singletrackpropertiesincludinglowcontactangle(<80◦_),_minimal_dilution_ratio_(5–13%)_and_high

sur-facequalitywereachievedarepresented.Thesepropertiesarerequiredfordepositingoverlappedtracks ofgoodsurfaceﬁnish,minimaldilutionandfreeofinter-runporosity.

1. Introduction

Lasercladdinghad beenshowntobeaneffectivemetal sur-facecoatingtechniquecapableofincreasingcomponentlifetime. Thetechniquehasseveraladvantagesovercompetingcoating tech-niquessuchasplasmacladding,arcweldingandthermalspraying. These include strong metallurgical bond at the clad–substrate interface(Chenetal.,1996),minimaldistortionofthesubstrate (Desaleetal.,2009),lowdilution(Huang,2011),minimalporosity (Sextonetal.,2002)andcontrollableheatinputoftenproducinga smallheataffectedzone(HAZ)(Huangetal.,2004).

Lasercladdinginvolvestheuseofahigh-precisionheatsource to create a melt pool by simultaneously melting the additive materialanda thinlayerofa substrate.Therelativemovement ofthelaserbeamandthesubstrateformsatrack.Thetrackismost

∗ Correspondingauthor.Tel.:+4401159514109;fax:+4401159513800. E-mailaddress:[email protected](A.T.Clare).

oftenreferredtoasacladbead.Additivematerialwhichiseither inpowderorwireformcanbedeliveredusingthreemethods. Pre-placingpowderintheformofslurryonthesubstratepriortoheat applicationislessﬂexiblecomparedwithothermethods.The coax-ialandsidefeedingofpowdercurrentlyhaswideapplicationsover sidefeedingofwireduetohighavailabilityofadditivematerialsin powderform.

Extensiveresearchinlaser claddingusingmetalpowderhas beenundertakenforenhancedsurfaceperformance.Consequently, arangeofhighcorrosionandwearresistantmaterialshadbeen processedinthisway.Desaleetal.(2009)researchedonthe ero-sion wear behaviourof Colmonoy-6 and Inconel 625 powders. Baldridgeetal.(2013)havereportedtheanalysisoflasercladding ofInconel690powderonInconel600forcorrosionprotectionin nuclearapplications.Cobalt-basedalloyshavealsobeenthe sub-jectofsomeinvestigationbyLusqui ˜nosetal.(2009).Quantitative characterisationofporosityinstainlesssteelsLENSpowdersand depositshavealsobeenreportedbySusanetal.(2006).Common observationsamongsttheseprocessesarehighsurfaceroughness, lowpowderdepositionrateandsusceptibilityofthecladto poros-ity usuallycaused by theentrapmentof gasin thepowder. As a result, cladding withpowder material is less economicalfor coatinglargeareas,especially,wherehighdimensionalaccuracy 0924-0136© 2013 The Authors. Published by Elsevier B.V.

http://dx.doi.org/10.1016/j.jmatprotec.2013.06.007

Open access under CC BY-NC-ND license.

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Duetoitscombinationoffavourablepropertiessuchashigh temperaturestrength,excellentcorrosionresistance,high ductil-ityandgoodstresscorrosioncrackingresistance,Inconel625(a nickelbasedsuperalloy)hasbeenthematerialchoiceforadiverse rangeofapplications.Theseincludegasturbineducting,furnace hardwareandcomponentsexposedtoseawater(Pauletal.,2007). Moreimportantly,thelowdilutionofthelasercladdingtechnique coupledwiththeexcellentcorrosionpropertiesofthealloyhad extendedtheapplicationsofInconel625lasercoatingtooilandgas industry.Down-holedrillingequipmentaremanufacturedfrom stainlesssteelsbecauseoftheirhighimpactstrength,reasonable corrosionresistanceandlowcost(Sueetal.,2010).Theresistance offeredbythesteelsagainstcorrosionis limitedbecausesteels sufferlocalisedcorrosioninspeciﬁcenvironments,particularlyin chlorideionrichsolutions(Mahmoodetal.,2012).Followingthis fact,thelifetimeperformanceofoff-shoreequipmentinharsh cor-rosiveenvironmentiscurrentlybeingincreasedbylasercoating thesurfaceofthesteelswithInconel625alloy.Todate,anumber ofstudieshavebeenreportedonlaserdepositionofInconel625 powder,forexample,themicrostructuralevolution(Dindaetal., 2009),optimisingprocessingparameters(Pauletal.,2007), thin wallmanufacture (Gao etal.,2011)andcorrosion propertiesof coatings(Tuominenetal.,2003).However,laserdepositionusing Inconel625wireasafeedstockmaterialratherthanpowderhas notbeenundertaken.

Laser cladding with lateral wire feeding system, compared withpowderbasedfeedingsystems,offersbetterrewardssuchas increasedmaterialusageefﬁciency(Syedetal.,2005),improved surfacequalityofthedeposit(Heralic,2009),lowercostof prepar-ingthewirematerials(KimandPeng,2000)andhighermaterial depositionrates(Syedetal.,2005).However,wirebasedsystems arehighlysensitivetochangesinprocessingcondition.Asaresult,it isimportanttoestablishabalanceofseveralimpactingprocessing parameterssuchaswiretippositioninthemeltpool,feedangle, feeddirection,laserspotsize,laserpower(P),wirefeedrate(WFR) andtraversespeed(V)beforeastablewiredepositionprocesscan beachieved.

Threewiretip positions, i.e.the centre, leadingand trailing edges,inthemeltpoolhavebeenidentifiedbySyedandLi(2005). Whenthewiretipwaspositionedatthetrailingedge,Syedand Li(2005)discoveredthatthedepositionprocesswasmainly char-acterisedbydroplettransferofwire(dripping)formingirregular beadswhereas smoothwiretransferwasonlyfoundpossibleat thecentreand leading edgeof themeltpool.Moket al.(2008) establishedthatwirefeedanglearound45◦givesthehighesttrack depositionefficiencyduringdiodelasercladdingofTi–6Al–4Vwire withfront feeding orientation. In thepast, optimisation of the processingparametersforNd–YAGlaserdepositionwithwireof ZE41A-T5,amagnesiumalloy,usingTaguchimethodfor param-eterdesign hadbeenundertaken (Cao etal., 2008).Theresults includethevariationof dilutionratiowiththemain processing parameters.However,astudyofthelaser depositionwithwire processcharacteristicsatvaryingprocessingparametersisabsent fromtheliterature.Also,significantlyfewauthorshavereportedon theinvestigationofthewettingangleusuallyreferredtoascontact angleoflaserdepositedwiretracksatvaryingcladdingconditions.

dictsInconel625wireﬁbrelaserdepositionprocesscharacteristics at varying processing parameters will be developed. Secondly, processingparametersatwhichacombinationoffavourable sin-gletrackpropertiesincludinglowcontactangle(<80◦),minimal dilutionratio(5–13%)andhighsurfacequalitycanbeachievedwill bedetermined.Thesepropertiesarequalitycriteriafordepositing overlappedtracksofgoodsurfaceﬁnish,minimaldilutionandfree ofinter-runporosity.

2. Experimental

2.1. Materials

Platesofdimension100mm×180mm×6mmweremachined fromausteniticstainlesssteelAISI304andusedassubstrate mate-rial.Theseweregritblastedandcleanedwithacetonebeforethe depositionrunssoastoimprovesubstratesurfacelaser absorptiv-ityandremovecontaminants,respectively.Theadditivematerialis Inconel625wireof1.2mmdiametersuppliedbyVBCgroup, Lough-borough,UK.Table1givesthechemicalcompositionsofInconel 625wireandAISI304stainlesssteel,asquotedbythe manufactur-ers.

2.2. Laserprocessing

Adiagramofthelaserdepositionsystemusedinthisstudyis showninFig.1.Depositionwasperformedusinga2kWYtterbium dopedﬁbrelaser(IPGPhotonics)operatingat1070nmwavelength. Thebeamwas focusedtoa small roundspotofapproximately 3.1mmat20mmawayfromfocusgivinga212mmworking dis-tancewithaGaussianenergydistribution.Inconel625wirewas “frontfed”atanangleof42±1◦ tothehorizontalsoastoaim thewiretipatthecentreofthemeltpool.AWF200DCwirefeeder (RedmanControlsandElectronicLtd.)wasused.

Single tracks were deposited, at varying processing param-eters, on the steel plates inside a transparent enclosure (bag) whichwasevacuatedandback-ﬁlledwithhighpurityargongas supplied at 0.42ls−1. The utilised processing parameters were selectedfollowingpreliminarytrialssoastoreducethenumber

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Fig.2. Trackcharacterisation(a)trackmetrics(b)SEMmicrographofatransverselysectionedsample.

ofexperimentalrunsrequired.Real-timeobservationofthe depo-sitionrunswasrecordedbyacameraattachedtoprecitecYW50 laserhead.Table2givesthedetailsoftheprocessingparameters usedforthetracksdeposition.Tracksweredepositedwith combi-nationsoflaserpowerandtraversespeedswithvaryingwirefeed ratesrangingfrom6.7mms−1untilstubbingwasobserved(i.e.the wiretipcollidingwiththesubstrate).Thisprocesswasrepeated forallpossiblecombinationsofprocessingparameterswithinthe selectedﬁxedrangeoflaserpowerandtraversespeed(totalling 125tracks).Twotracksweredepositedateachcladdingcondition toprovideadegreeofveriﬁcation.

2.3. Trackcharacterisation

Fig.2ashowsaschematicdiagramoftypicaltrackgeometry. Thetracksheightsandwidthsweremeasuredatthreedifferent pointsalongtheirlengthsusingaTaylorHobsonsurfaceproﬁler (TalysurfCLI1000). For the purposeof microstructural investi-gation, track samples were transversely sectioned, mounted in conductingresinandsequentiallygroundandpolishedtoa1␮m surfaceﬁnish.Then,thetracksampleswereelectrolyticallyetched using70% orthophosphuric acidin water (typically6V for 3s). Thetracksmicrostructureswereexaminedunderscanning elec-tronmicroscopy(SEM)usingabackscatteredelectron(BSE)signal. QuantitativeenergydispersiveX-rayanalysis(EDXA)wasutilised indeterminingtheelementalcompositionofFeinthetracksby conductingareascan(200␮m×200␮m)analysisalongandacross theheightofeachcross-sectionedtrack,asshowninFig.2b.

2.4. Deﬁnitionofterms

Energyperunitlengthoftrack(EL)inJmm−1 isacombined

effectoflaserpower(P)inWattsandtraversespeed(V)inmms−1, anditisdeﬁnedbyEq.(1).Thedepositionvolumeperunitlengthof trackpass(DVL)inmm3mm−1hasthetraversespeedandwirefeed

rate(WFR)inmms−1asthedeterminingvariables.Theconstant‘A’ inEq.(2)isthecross-sectionalareaofthewireinmm2_.

EL= P_V (1)

Table2

Processingparameters.

Parameters Value Unit

Laserpower 1.0–1.8 kW

Wirefeedrate 6.7–23.3 mms−1

Traversespeed 1.7–8.5 mms−1

Separationdistancebetweentwoconsecutivetracks 10 mm

Argongasﬂowrate 0.42 ls−1

Wirediameter 1.2 mm

Wirefeedingangle 42±1 degrees

DVL= A×_VWFR (2) ˇ=2arctan

₂_H W

(3) = c(Xc+s−Xc) s(Xs−Xc+s)+c(Xc+s−Xc) (4)

Thecontact angle(ˇ)wascalculated fromthevalues of the trackheight(H)and width(W)using Eq.(3)(deOliveiraetal., 2005)whilethedilutionratio()wasdeterminedfromthe com-positionofthetrackusingEq.(4)(Toyserkanietal.,2005).cand

s inEq.(4) arethedensitiesofthefeedmaterial(Inconel625

wire;8.44×10−3gmm−3)andsubstrate(AISI304stainlesssteel; 8.04×10−3gmm−3),respectively.Xc+sandXsarethemeanweight

percentofFeintotalsurfaceoftrackregionandsubstrate, respec-tivelywhileXcistheweightpercentofFeintheadditivematerial. 3. Resultsanddiscussion

3.1. Wiredepositioncharacteristics

Asthewirefeedratewassequentiallyvariedforeach combina-tionoflaserpowerandtraversespeed,entirelydifferentdeposition processcharacteristicswereobserved.Theobservedcharacteristics werewiredripping,smoothwiretransferandwirestubbing.These aretypicalofwirelaserdepositionprocess.However,eachmaterial systembehaveddifferentlyateveryconditionoflaserdeposition process. Inconel 625coatings onoiland gas pipelines is being increasinglyutilisedbecauseofitsexcellentprotectionagainst cor-rosion(Xuetal.,2013).Asaresult,optimisingInconel625wirelaser depositionprocesstoproducingcontinuoustrackwithacceptable dimensionisessentialtoitsapplicationin thisindustry.A pro-cessmapvalidforthefibrelaserdepositionofInconel625wireof Ø1.2mmforlaserpowerrangeof1.0–1.8kW,traversespeed ran-gingfrom1.7to5.0mms−1andwirefeedrate6.7–23.3mms−1was developed.AsshowninFig.3,fivedifferentregionswereclearly definedinthemapwith1–5representingdripping,drippingmay occur,smoothwireflow,stubbingmayoccurandstubbingregions, respectively.Eachprocessingconditionwasrepresentedbyapoint onthemap.Thecombinedparameteronthey-axisofthemapwas foundbydividinglaserpowerbythetraversespeed(seeEq.(1)). Wiredepositionvolumeperunitlengthonthex-axisisafunction ofwirefeedrate,traversespeedandcross-sectionalareaofthefeed wireatagivenprocessingcondition(seeEq.(2)).

Fig. 4 presents the typical examples of tracks deposited by depositionprocess characterisedwithdrippingof wire(droplet transfer),smoothtransferofwire(smoothdeposition)andstubbing ofwire.Theidealscenario(i.e.claddingconditionsthatproduce trackofhighsurfacequalityandacceptabledimensions)isfound whenthereissmoothtransferofwireintothemeltpool.Thiswas observedwheneverthewiretipmeltedatthepointorclosetothe

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Fig.3. AprocessmapforInconel625wirelaserdepositedtracks.

pointofintersectionwiththemeltpool.Theprocessingconditions thatproducedsmoothtransferofwirearecontainedintheregion 3oftheprocessmap.

Whenthewirefeedratewasexcessivelylowforafixed combi-nationoftraversespeedandlaserpower,intermittentdrippingof wirewasobserved.Thisproduceddiscontinuoustracksasshownin Fig.4.Ataverylowwirefeedrate,thewiretipinteractedtoolong withthelaserbeamsuchthatitabsorbedheatenergysufficientfor itsmelting.Asaresult,thewiretipmeltedbeforeintersectingwith themeltpool.Thisproducedintermittentdrippingofmoltenwire asthesubstratetraversed.Similareffectwasobservedwhenever theenergyperunitlengthoftrackwasexcessiveforafixedwire depositionvolumeperunitlengthoftrack.

Atacladdingconditionwhenthewirefeedratewasexcessively highforafixedcombinationoftraversespeedandlaserpower,the feedwireinteractedbrieflywiththelaserbeam.Asresult,thewire enteredthemeltpoolinanearlysolidformresultinginthecollision ofthewiretipwiththesolidsubstrateatthebaseofthemeltpool.A collisionwiththesubstratecausedthewiretiptomoveawayfrom thecentreofthemeltpool.Intheprocess,thewirewaseventually meltedbytheenergyinthemeltpoolandsolidifiedastrackswith anirregularshape.Atanextremelyhighwirefeedrate,thewire remainedunmelted.Thiswasduetothefactthatwiredeposition volumeperunitlengthoftrackwastoohighforthegivenenergy perunitlengthoftrack.

Fig.4.TypicaldepositsofInconel625wire.

thenwirestubbing.Thisshowsthatthewiredrippingcanbe elim-inated,asexpected,byeitherreducingtheenergyperunitlength oftrackorincreasingthewiredepositionvolumeperunitlength oftrack.Also,wirestubbingcanbereversedtoidealscenarioby eitherincreasingtheenergyperunitlengthoftrackordecreasing thewiredepositionvolumeperunitlengthofthetrack.

Region 2 (i.e. wire dripping may occur region) formed the boundarybetweenthedrippingregionandsmoothwire deposi-tionregion.Laserdepositionprocessesperformedattheconditions correspondingtothisregionproducedinconsistentcharacteristics becauseeachoftheseprocesseswerecharacterisedwithdripping andsmoothwiretransfereffectsafteratleasttwotrials.Asaresult, itwasdifﬁculttocorrectlyclassifythemeitherintodrippingor smoothdepositionregion.

Region4istheboundarybetweenthesmoothdepositionregion andthewirestubbingregion.Duetoinconsistenceintheir pro-cesscharacteristics,claddingconditionsthatgavedepositionrun ofbothwirestubbingandsmoothwiretransferafteratleasttwo differenttrialsweregroupedinthisregion.Finally,themap pre-dictsthatsmoothwiretransfermaynotbepracticable,withthis arrangement,whencladdingbelowenergyperunitlengthoftrack of200Jmm−1.

3.2. Cladcharacteristics 3.2.1. Width–heightaspectratio

Thewidth–height(W–H)aspectratiowascalculatedfromthe resultsobtainedfromtheheightandwidthmeasurementsofthe tracks.Since,pastworkshaveclearlyindicatedthattrackaspect ratioissigniﬁcanttodepositinginter-runporosityfreeoverlapped tracks(PinkertonandLi,2008),aspectratioofsingletrackdeposits canthereforebeusedasaqualitycriterionforthedepositionof overlappedtracks.

Fig.5showsthatthetrackaspectratioincreaseswith increas-ingthetraversespeedandlaserpowerbutwithdecreasingthewire feedrate,provided,otherfactorsremainconstant.Similarresults werefoundfor ﬁbrelaser micro-claddingofCo-basedalloys on AISI304stainlesssteel(Lusqui ˜nosetal.,2009).Theresponseof theaspectratiocanbeexplainedbythewirevolumedeposited per unit length of track. Decreasing the wire feedrate and/or increasingthetraversespeedreducedthewiredepositedvolume perunitlengthoftrack.Thisresultedintrackofreducedheight. However,the track width wasinvariant withthe wire deposi-tionvolume(mm3_mm−1_)._These_effects_produced_decreased_aspect

ratio.Higheraspectratioobtainedathigherpowerisdueto pro-nouncedﬂatteningeffect(increaseinwidth)oflaserpoweronthe trackgeometry.Sincewidthisthenumeratorintheratiotherefore anychangethatincreasesitand/ordecreasesH(denominator)will increasethevalueoftheratio.

3.2.2. Dilutionratio

Generally, dilution is the percentage of thetotal volume of thesubstratematerialinthetrackcontributedbymeltingofthe substrate.Thoughitisundesirableincladdingprocesses,some min-imum(about3–8%)(Qianetal.,1997)isrequiredbeforeafully densebondisachievableinatrack.

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Fig.5. Variationoftrackaspectratioasafunctionofthemainprocessingparameters(a)P=1.8kWand(b)P=1.4kW.

Dilutionratioanalysiswascarriedoutfromthecompositionof thetracksasdescribedinSection2.4.AsshowninFig.6,elemental compositionanalysis(i.e.EDXA)establishedthatFecontent,hence, thepercentagedilutionoftheexaminedtracksamplesincreased withincreasinglaserpowerandtraversespeedbutwithdecreasing wirefeedrate.Asthelaserpowerwasincreased,ahighervolume ofthesubstratewasmeltedduetoincreasedenergyinput.Also, therewassufﬁcientmixingandvigorousmeltpoolmovement.This causedanincreasedpercentageofthemoltensubstrate(mainly Fe) mixing withthetrack layerthus producing higher dilution ratio.

Atincreasedwirefeedrate,morewirevolume(duetoincreased depositionrate)wasdepositedintothemeltpoolproducingbigger track.Also,therewasincreasedlaserenergyinterruptionbythe feedwirecausingsigniﬁcantreductioninthefractionofenergy reachingthesubstrate.Asaresult,lowmelteddepthintothe sub-stratewasobserved.Also,theviscosityofthemeltpoolisbelieved tobehigherathigherWFRthereforereducingthevigour,hence,

mixinginthemeltpool.Eventually,therewasreduceddilutionof Fefromthesubstrate.

Whenthetraversespeed wasincreased,two thingsbecame apparent.Firstly,thedepositedwirevolumeperunitlengthoftrack reduced,producing smallertrack.Secondly, theenergyperunit lengthoftrackalsodecreasedcausingreducedmelteddepthinto thesubstrate.However,asshowninFig.7,thechangeinmelted depthintothesubstrateisrelativelyinsigniﬁcantcomparedwith thechangeinthetrackvolume.Asaresult,increaseindilutionratio wasobservedinthetrackasthespeedincreased.

3.2.3. Contactangle

AsshowninFig.6,contactanglewasfoundtoincreasewith increasingwirefeedratebutdecreasedwithincreasingtraverse speedandlaserpower.Theresultsshowthatapartfromthe sur-facetension,processingparametersalsoinﬂuencethewetting(i.e. contactangle)oflaserdepositedtracks.Fig.8clearlyrevealedthat anincrease inwire feedrateand/ordecrease intraversespeed

Fig.6. Variationofdilutionratioandcontactanglewiththemainprocessingparameters.(a)P=1.8kW,WFR=13.3mms−1_,_(b)_P₌_1.8_kW,_V₌_1.7_mm_s−1_and_(c)_V₌_1.7_mm_s−1_, WFR=13.3mms−1_.

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Fig.7. Etchedopticalmacro-photographsoflasertrackcross-sectionsforInconel625wireatlaserpowerof1800Wandwirefeedrateof10mms−1_.

(i.e.increasingthewiredepositedvolumeperunitlengthoftrack) resultedintracksbecomingmorespherical.Atalowwire depo-sitionvolumeperunitlengthoftrack,a parabolicshapedtrack of contact angle lower than 90◦ wasformed. However, as the wirefeedrateincreasedortraversespeeddecreased,morewire wasdeposited perunitlengthoftrack untilitwassufﬁcientto forma trackstripwithamoresphericalshape incross-section. Furtherincreasestowiredepositionvolumeresultedinswollen ﬂanksofthetrackthusproducing trackwithanobtuse contact angle.

Highenergyperunitlengthoftrackresultingfromincreased laserpowerproducedhottermeltpool.Thehighenergymeltpool expeditedthemeltingofthewire,increasedtheﬂuidityandvigour ofthemeltpool.Thiscausedthemoltenpooltospread,insteadof buildingheight,awayfromitscentre.Asaresult,thesolidsubstrate at meltpoolboundary melted and the meltpoolsize increased. Eventually,widertrackswithlowcontactangleswereformed.

3.2.4. Overlappingtracks

Geometricalcharacterisationofallthedepositedtracksrevealed thatthereisasharpcontrastinthegrowthtrendsofcontactangle anddilutionratiowiththeprocessingparameters.

Theconcernwastodeterminesuitableprocessingcondition(s) thatgivegoodsurfacequalitytrackswithlowcontactangle(<80◦) and minimal dilution ratio(ranging between5% and 13%).The combinationofthesesingletrackpropertiesisimportantforthe depositionofoverlappedtracksofhighsurfacequality,minimal dilutionandnointer-runporosity.Fediffusionfromthesubstrate intothetrackhasadeterioratingeffectonthecorrosionbehaviour ofthesuperalloy(ZareieRajanietal.,2013).Asaresult,a mini-mumdilutionratiobetween3%and8%hadbeenestablishedtobe appropriateforobtainingafullydensetrack-substratebond. Val-uesoutsidethisrangewereconsideredundesirable.Inthisstudy, processingconditionsthatproducedsingletrackswith5–13% dilu-tionratiowereselectedfordepositingoverlappedtracksbecauseit

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Table3

Processingconditionsatwhichacombinationoffavourablesingletrackpropertiesincludinglowcontactangle(<80◦_),_minimal_dilution_ratio_(5–13%)_and_high_surface_quality wereachieved.

S/N Laserpower(kW) Traversespeed(mms−1) Wirefeedrate(mms−1) Processcharacteristics Dilution(%) Contactangle(degrees) Aspectratio

1 1.8 1.7 10.0 Smoothwiredeposition 11.9 75 2.6

waspredictedthatreduceddilutionratioisobtainableinthe over-lappedlayers.Thisisdueinparttotheadditionalheatingofthe adjacenttracks.Theprocessingconditionsatwhichthe combina-tionoffavourablesingletrackpropertieswasfoundarepresented inTable3.

Excessivelylowenergyperunitlengthoftrackcausedmajority ofthedepositionsperformedat1.0kWlaser powertobe char-acterisedbywirestubbing.Processingparameterswheresmooth deposition wasobserved, the desirable combination of contact angleanddilutionratiowasnotachieved.

4. Conclusion

Inthis work,a processmap for thefibrelaser depositionof Inconel625wire predictingtheprocesscharacteristics at vary-ingprocessingparameters hasbeendeveloped. Energyperunit lengthof trackand wire depositionvolume per unit length of tracksignificantlyinfluenceboth thedepositionprocess charac-teristicsandthetrackgeometricalcharacteristics.Excessivelylow andhighwiredepositionvolumeperunitoftrackforagivenenergy perunitlengthoftrackresultedinwiredrippingandwire stub-bing,respectively.Tracksofhighsurfacequalityandacceptable dimensionweredepositedwhenevertherewassmoothtransfer ofwire.Atenergyperunitlengthoftrackbelow200Jmm−1,itis impracticable,forthesetupemployedinthisstudy,to success-fullydepositInconel625wiretrackofgoodsurfacequalityand acceptabledimension.

Theindividualeffectsoflaserpower,traversespeedandwire feedrateonthetrackcharacteristicswereinvestigatedandthe followingconclusionsweredrawn.

• Itwasfoundthatthecontactangleincreaseswhereasdilution ratioandaspectratiodecreaseswithincreasingwirefeedrate. • Boththedilutionratioandaspectratioshowpositivewhereas

contactangleshowsnegativedependencyonthetraversespeed. • Dilutionratioandaspectratiovarieddirectlybutcontactangle

variedinverselywiththelaserpower.

Finally, processing conditions at which a combination of favourable single track properties including low contact angle (<80◦),dilutionratiorangingbetween5%and13%andhighsurface qualitycanbeachievedarepresented.

Thefutureworkincludesthemicrostructuralcharacterisationof thesingletracksaswellasthecharacterisationandcorrosionstudy oftheoverlappedtracksdepositedatthedeterminedconditions presentedinthisstudy.

Acknowledgements

TheauthorswouldliketothankPetroleumTechnology Devel-opmentFund,Nigeriafor sponsoringthis research.Theauthors alsoacknowledgetheexpertiseandtechnicalinputfromMr.Stuart Branston.

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