Wear and mechanical properties of Al6061/SiC/B4C hybrid composites produced with powder metallurgy

(1)

metallurgy

Halil

Karakoc¸

a,∗

_{, ˙Ismail}

_Ovalı

b

_,

_Sibel

_Dündar

c

_,

_Ramazan

_C¸

_ıtak

c

a_Department_of_Mechanical_Program,_Hacettepe_University,₀₆₉₃₅_Ankara,_Turkey b_Department_of_{Manufacturing}_Engineering,_Pamukkale_University,₂₀₁₆₀_Denizli,_Turkey c_Department_of_Metallurgy_and_Materials_Engineering,_Gazi_University,₀₆₅₀₀_Ankara,_Turkey

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received30October2018 Accepted2September2019 Availableonline26September2019

Keywords: Aluminum B4C SiC Hybrid Extrusion Mechanicalproperties Wear

a

b

s

t

r

a

c

t

Thisstudyinvestigatestheproductionofvariousreinforcedandnon-reinforcedcomposite materialsusingpowdermetallurgy(PM).Itpresentsthenewapproachintooptimizethe mechanicalpropertiesofhybridcomposites(Al-SiC-B4C)producedwithpowderextrusion

process.A16061powdersareusedasthematrixmaterialandB4CandSiCpowdersare

usedasthereinforcementmaterials.Matrixandreinforcementmaterialsaremixedina three-dimensionalmixer.Themixturesarethensubjectedtocoldpressingtoformmetal blocksamples.Blocksamplesaresubjectedtohotextrusion inanextrusionmoldafter beingsubjectedtoasinteringprocess.Thisproducessampleswithacross-sectionalarea of25×30mm2_._These_extruded_samples_were_subjected_to_T6_heat_treatment._The

com-positematerialsproducedareexaminedintermsofdensity,hardness,transverserupture strength,tensilestrength,andwearresistance.Furthermore,opticalmicroscopy,scanning electronmicroscopy,energy-dispersiveX-rayspectroscopyandXRDareperformedto exam-inethemicrostructure,surfacefractures,andsurfaceabrasion.Inthisstudy,highdensity Al6061/B4C/SiChybridcompositematerialsweresuccessfullyproduced.Afterextrusion,

somemicroparticleswerefoundtocrack.Thehighesthardnessoccurredin12%B4C

rein-forcedcomposites.ThelowesthardnesswasobtainedinAl6061alloywithoutreinforcement. Thehighesttensilestrengthoccurredin12%SiCparticlereinforcedcompositematerial.The highestwearresistancewasobtainedfor9%B4C+3%SiCsamplesduetothehardnessofB4C

andthegoodadhesionpropertiesofthematrixandSiC.

∗ _{Corresponding}_author.

E-mail:halil.karakoc@hacettepe.edu.tr(K.Halil).

1. Introduction

Superiorpropertiesofmetalmatrixcomposites(MMC),such astheirhighstrength,lowdensity,andhighmodulusof elas-ticity,makethesematerialsindispensable[1].Differentmatrix materials,suchasAl,Mg,andTi,areusedinMMCs[2].Among these,Alisoneofthemostpreferredmatrixmaterialsbecause https://doi.org/10.1016/j.jmrt.2019.09.002

(2)

ofitslightweight,goodeffectiveheatandelectrical conductiv-ity,andhighcorrosionresistance[3].ManyAlalloys(eg2xxx, 5xxx,6xxxand7xxx)areusedindustrially[4].6xxxseriesof aluminumalloyshavegoodmachinabilityandextrudability [5].Byaddinghardceramicparticlesintothesealloys, abra-sionresistanceandmechanicalpropertiescanbeimproved [6].Particlesofboroncarbide(B4C)andsiliconcarbide(SiC),

themostfavoredreinforcementmaterialsamongaluminum matrix composites (AMC)materials, strengthen the matrix structureandprovidehighresistance,goodwearresistance, and high thermal stability [7,8]. Today, two different types ofceramicparticles are incorporated into the Almatrix to producehybridcompositematerials[9].Dual reinforcement elements used inhybrid composite materialscan improve mechanicalpropertiesandcostofcompositescanbereduced [10,11].Inaddition,theweightofthecompositeformeddue tothereinforcingelementsusedcanbereduced[12].The alu-minum hybridcomposite devices alsoshow that it can be usedinplaceofconventionalmaterialsinadvanced applica-tions[13].ManydifferenttechniquessuchasPMandcasting areusedintheproductionofMMCmaterials[14].Whenwe comparethecastingtechniquewiththePMtechnique,some advantagesofPMcometotheforefront.Intheproductionof PM,nochemicalreactionoccursbetweenthematrixphase andthereinforcingelement,sinceproductionoccursatlow temperatures.Inaddition,highamountsofceramicparticles canbeaddedintothematrixphase[15,16].

Themainaimofthisstudyistoproducehybridcomposite materialswhichhaveimprovedwearandmechanical proper-tiesbyaddingB4CandSiCparticlestoAl6061alloy,whichhas

goodmachinabilityandextrudabilityandalsohasgood cor-rosionresistance.Inthisstudy,non-reinforced(Al6061alloy), conventionalreinforced(Al6061/B4C-Al6061/SiC)and

dou-blereinforced(Al6061/B4C/SiC)compositematerialswere

producedbyusingextrusionprocessinPM.Themechanical properties,suchashardness,bendingstrength,and elonga-tion,wereinvestigatedandcomparedbyevaluatingfracture surfacesandmicrostructures.Microstructuralanalyseswere carriedoutusingscanningelectronmicroscopy(SEM).

2. Experimental

procedures

2.1. Materialsandmethods

Thepowdersizeofthe6061seriesaluminumwastakentobe smallerthan100␮m(suppliers:BeijingXingRongYuan

Tech-nologyCompany,China).ThechemicalcompositionofAl6061 isshowninTable1.TheAMCmaterialswerereinforcedwith 3wt.%B4Cand9wt.%SiC;6wt.%B4Cand6wt.%SiC,9wt.%

B4C and 3wt.% SiC, and 12wt.% B4C (<10␮m)and 12wt.%

SiC(<8␮m).SiCandB4Cceramicpowderswhichwereused

asreinforcingelementswere obtainedfrom Nurol Technol-ogyCompanyinTurkey.Thepropertiesofmetalandceramic powdersusedinthe productionofcompositematerialsare giveninTable2.AﬂowchartoftheprocessisshowninFig.1. First,themixtureratiosoftheAl6061andB4Cpowderswere

determined and separately mixed for 30min in a Turbula three-dimensionalmixer.Next,Al6061andSiCpowderswere preparedwiththesameparameters.Allofthevolume frac-tions are showninTable 3. During theexperimentalwork, the reinforcementparticleswere addedslowlyfora homo-geneousdistribution.Themixedcompositionswerepressed at300MPaandsinteredat550◦Cfor1h.Finally,the compos-itematerialswereextrudedatthesametemperatureusinga pre-heatedhydraulicextrusionmoldandtakingtheformof shapedmetalblocks(Fig.2aand b).Thecomposite materi-alsobtainedafterextrusionweresubjectedtoT6agingheat treatment.Thecompositematerialsweresubjectedto1h dis-solutionat530◦Candthenimmediatelycooledinwater.The cooledsamplesarethenartiﬁciallyagedfor8hbyheatingat 175◦Cwithaheatingspeedof10◦C/min.

2.2. Analysisofmicrostructureandmechanical properties

Inthisstudy,Al6061wasusedasametalmatrixandB4Cand

SiC powders asreinforcement materials.Fig. 3shows SEM imagesandparticulatesizedistributionsofthepowdersused inthestudy.TheanalysesshowthattheAl6061matrix pow-dershadirregularsphericalformswithagrainsizeofbelow 100␮monaverage.TheB4Cpowders,ontheotherhand,were

foundtohaveacomplexandcorneredformwithgrainsizes varyingbetween1and 10␮m.TheSiCpowdershada com-plex formwith sizesvarying between1 and 8␮m. For the metallographicexamination,threesamplesofeach powder atsizesof24×18×5mmwere cutusingadiamondcutter inthedirectionofverticalextrusion.Aftertheywerecut,the samplesweresubjectedtocoldmounting(moldingbyepoxy resin).Then,usingdecoupage,thesamplesweresandedwith emerypapersof400, 600,800,1000,and1200grits, respec-tively.Aftersanding,thesampleswerepolishedbymeansof diamondsuspensionwithfeltsof6,3,and1␮m,respectively. Thispolishingprocedureminimizedthesurfaceroughness.

(3)

Fig.1–Flowdiagramofprocess.

Table3–Volumefractionofmaterials.

Materialmixingratio(%) Weightofmixture

proportions(g)

Sample Al6061 B4C SiC Al6061 B4C SiC

1 100 0 0 400 0 0 2 88 3 9 352 12 36 3 88 6 6 352 24 24 4 88 9 3 352 36 12 5 88 12 0 352 48 0 6 88 0 12 352 0 48

Fig.2–Pressingthepowdermetaloftheblocksamples(a),TheExtrudedcompositematerials(b).

Thesampleswerethensearedfor15susinga1-mlHF+200-ml H2Osearingsolution.

ALeicaDM4000Mopticalmicroscopewasusedtoperform amicrostructuralexaminationofthecompositematerials.A JEOLJSM6060LVscanningelectronmicroscopewasusedto investigatetheinterfacialconnectioncohesionbetweenthe reinforcementmaterials(B4C,SiC)andmainmaterial(Al6061). In the composites produced, and energy-dispersive X-ray spectroscopy(EDS)analyseswerealsoperformedonthesame SEMmicroscope.ASartoriusscaleof0.1mgsensitivitywas

usedtoperformdensitymeasurementsoftheAl6061/B4C/SiC compositematerialsproducedusingtheArchimedesmethod. TheBrinellmethodforhardnessmeasurementwasusedto investigatethehardnessofthecompositematerialsthatwere producedusingthePMmethodandsubjectedtotheT6 age-ingprocess.Hardnessmeasurementswereperformedusing anEMCO-TESTDuraVision200hardnessmeasurementdevice using2.5mmballendanda31.25kgfload.Threesamplesof eachtypeofcompositematerialproducedwereselectedfor mechanicaltestsoftensileandtransverserupturestrength.A

(4)

Fig.3–SEMmicrographsofAl6061andB4CSiCpowders,particulatesizedistributionsofpowders.

JohnfordT35CNClatheworkbenchand aJohnfordVMC550 CNC planer with three axes (manufactured in the Manu-facturing Engineering Departmentof GaziUniversity) were usedtopreparethesamplesforthemechanicaltest. Sam-pleswerepreparedtoASTME8Mstandardsinthedirection of extrusion using the composite materials obtained after the extrusion process. Tensile tests were performed using anInstron3369universal testing device with 50kNtensile and compression capacity at1mm/min at room tempera-ture.Tensilestrengthsandpercentageelongationvalueswere producedandrecordedonacomputerconnectedtothe ten-siletestingdevice.Sampleswithsizesof31.7×12.7×6.35mm werepreparedforthetransverserupturetestsincompliance with“MPFI–411998”standards. Thetransverserupturetests wereperformedwithatransverseruptureapparatusspecially preparedwiththeInstron3369universaltestdevicewith50kN tensileandcompressioncapacity.Thetestswereconductedat roomtemperatureandataspeedof1mm/min.X-ray diffrac-tion(XRD)ofcompositematerialswasperformedonBruker brandD8DiscovermodelXRD.CuK␣radiation(K␣=1.54056) wasusedformeasurements.

XRDresultswereanalyzedformicrostructural characteri-zationofcompositematerials.Theaveragecrystallitesizewas calculatedfromthefullwidthathalfmaximum(FWHM)ofthe XRDpeakbyusingScherer"sEq.(1)[17,18].

Dp=(k␭)/(Bcos␪) (1)

Where;

Dp=Averagecrystallitesize, ␭=X–Raywavelength,

B=FWHMofthediffractionpeak, ␪=Angleofdiffraction,

K=Scherer’sconstantoftheorderofaboutunity(0.94)for usualcrystals.

2.3. Analysisofwearproperties

Thewear testswere carried out using apin-on-disk wear-testingdevice accordingtoASTMG132-96.Samplesurfaces weregroundwith80SiCpaperforremovingroughsurface, thentheAMCtestpin,withadiameterof10mm,wasﬁxed andacounterfaceabrasivedisk(abrasivepaperof200grit) wasusedduringthetest.Theweartestswereperformedat distancesof100,200, and 300m,ataspeed of1.2m/s and withimposedloadsof5,10,and15N.Thecoefﬁcientof fric-tionbetweenthepinspecimenandthediskwasdetermined with a load cell. Prior to measurement, the sampleswere cleanedwithacetonetoremovesurfacecontaminants,dried, andthenweighedusinganelectronicbalancewitha resolu-tionof0.001mg.

Apin-on-ballweartestwasappliedtoexaminethe abra-sionbehavioroftheAMCmaterials.Thistestwascarriedout withavelocityof2.8m/sandloadconditionsof5,10,and15N.

3. Experimental

results

3.1. Microstructure,densityandmechanical characterization

Optical microscope was used to acquisition images that revealedtheparticledistributionofthecompositematerials afterverticalextrusion(Fig.4).IntheimageofAl6061,nopores areobservedinthemicrostructure(Fig.4a).Thisresultedfrom thehighdensityofthematerialthatoccurredinparallelwith theplasticdeformationduringtheextrusionprocess.Forthe microstructuresofthecomposites reinforcedwithB4C and

SiC,thisstudyfoundthatB4C/SiCparticlesin3%B4C+9%SiC

compositesgenerallyexhibitedahomogenousdistributionin thematrix.In6%B4C+6%SiCand9%B4C+3%SiCcomposites,on

theotherhand,itwasobservedthattheformationof agglom-erationsincreasedinparallelwiththeincreaseinB4Ccontent.

(5)

Fig.4–Afterextrusionopticalmicroscopeimagesof(a)Al6061(b)3B4C9SiC(c)6B4C6SiC(d)9B4C3SiC(e)12B4C(f)12SiC.

While12%B4Ccompositesexhibitedahigherlevelof

agglom-eration,lownumbersofporesisformedinthemicrostructure. Itwasobservedthatmicrocracksareformedinsomeparticles, asaresultoffrictionbetweenparticlesduringtheextrusion process.Thestudy alsodemonstrated that SiC particles in 12%SiCcompositesdisplayedahomogenous distributionin thematrixstructure.

InFig.5,XRDpeaksofAl6061alloyandB4C,SiCparticle

reinforcedcompositematerialsaregiven.TheAl,B4CandSiC

peaksin theﬁgurewere foundbylooking atthe literature [20–22].When theXRD peaksare examined,it isseenthat Al(111) andAl(200)peaks aremoreextensiveanddistinct thanotherpeaks.B4CandSiCpeaksarelessprominent.The

averagecrystalsizesofthecompositematerialswere calcu-latedaccordingtoSchererequationandcomparedwitheach other.In literaturestudies,it isknown thatmicro stresses increasewithdecreasingcrystalsize[23,24].Increasedmicro tensionincreasesthestrengthofthematerial.Consequently, thehighestvaluewasobservedinAl6061alloywith45.8nm. The lowest value was found in 12SiC composite material with33.1nm.Thisexplainswhythe12SiCcomposite mate-rialexhibitssuperiorstrengthpropertiesthanAl6061material. The12B4C reinforced composite materialwas found to be

larger than the 12SiC particle reinforced composite mate-rial having an average crystal size of less than Al6061.In hybrid composite materials, average crystal size increased withincreasingB4Cratio.

CompositematerialswithanAl6061matrixandreinforced with B4C and SiC particles in different proportions were

producedbymeansofaPMtechnique.Zhengetal. investi-gatedcomposite materialsreinforced withAA2024/20%B4C,

whichthey producedvia mechanical milling,hot pressing, andhotextrusion,withrespecttomechanicalpropertiesand microstructure.Thesamplessubjectedtohotpressingunder 823Kand400MPawerealsosubjectedtohotextrusionatthe sametemperature, whichproduced compositeswith

maxi-mumdensity.Theyobservedthatafterthehotextrusionthe B4CparticlesexhibitedaregulardistributionintheAA2024

matrixandtheporesformedduringthesinteringprocess dis-appeared[19].

Lowdensityreducesthemechanicalpropertiesof compos-ites.Forthisreason,inthepresentstudy,thesampleswere subjectedtohotextrusionandthenweresinteredaftercold pressinginordertoproducehigh-densitysamples.

Fig. 6ashowstheoreticaland experimentaldensity rela-tionships versus reinforcement rates for the composite materialsproduced.AsFig.6ashows,theaveragedensities ofallthepowdermetalblockssubjectedtocoldpressingare over89%.Inthecold-pressedsamples,Al6061hadthe high-est density(91.03%)and12%B4C-reinforcedcompositeshad

thelowestdensity(89.55%).WhilethedensitiesofAl6061and 12%SiCareclosetoeachother,thedensitiesdecreasein par-allelwiththeincreaseinB4Cratio.Theaveragedensitiesin

all thesamplessubjectedtoextrusionwere observedtobe 99%.Thissituation resultedfrom thehighplastic deforma-tion ofthecompositesduringtheextrusionprocess.While thehighestdensitywasobservedintheAl6061alloy(99.74%), compositematerialsreinforcedwith12%B4Chadthelowest

density(99.02%).

Fig.6showsthehardness,transverseruptureresistance, andtensileresistancevaluesofthecompositematerials pro-duced.Thereinforcedcompositeshadhigherhardnessvalues compared with the reinforced Al6061 alloy (Fig. 6b). While Al6061hadanaveragehardnessvalueof50HB,the12%B4C

compositedisplayedthehighestvalueofhardnesswith76HB. ItisknownthatinanAlmatrixthehardnessvaluesof com-positesgenerallyincreaseinparallelwiththeincreaseinB4C

ratio[25].Theaveragehardnessvaluein12%SiCcomposites wascalculatedtobe54HB.IncompositesreinforcedwithB4C

andSiC,thehardnessvaluesdisplayedanincreaseinparallel withtheincreaseinB4Cratio.Itwasobservedthatceramic

(6)

Fig.5–X-raydiffractionpattern(a)andavaragecrystallitesize(b)ofcompositematerialsproducedwithhotextrusion.

Fig.6–Densitychangesandmechanicalpropertiesofthehybridproducedcomposites.

theincrease inhardnessbyformingastraininthe matrix structure.Mechanicalpropertiesofaluminumalloyscanbe improvedbytheadditionofceramicparticles.siliconcarbide, alumina,bariumchlorideetc.Withtheadditionof reinforce-mentstoaluminumalloy,thehardnessvalueofthematerial increaseswhileductilevaluedecreases[26].

Thetransverserupturestrengthwasfoundtobe402.5MPa in composites reinforced with 12%SiC (Fig. 6c). The com-posite12%B4C,whichdisplayedthehighesthardnessvalue,

showedthelowesttransverserupturestrengthwith358MPa. Transverserupture strength decreasedin parallel withthe increaseinB4CratiointheB4CandSiCcomposites.The

trans-verserupturestrengthsof3%B4C+9%SiC,6%B4C+6%SiC,and

9%B4C+3%SiCcompositeswerecalculatedtobe378,367,and

362MPa,respectively.

Intheopticalmicroscopeimages,itcanbeseenthatB4C

reinforcementelementsformanagglomerationinthematrix structure.Itcanalsobeobservedinthemixedcompositesthat

agglomerationsincreasedinparallelwiththeincreaseinB4C

content.

Thetensilestrengthvaluesofthecompositematerialsthat weresubjectedtotensiletestsinthesameenvironmentare shown in Fig. 6d. While the Al6061 materialdisplayed the lowesttensileresistancewith174MPa,the12%SiCcomposite hadthehighestvalueat185.1MPa.Thisstudythus demon-stratedthatinB4C/SiCcomposites,tensileresistancevalues

tendtodeclinewithincreasingB4Creinforcementratio.As

is the casewiththe transverse rupture values, agglomera-tionsinthematrixstructurealsohadaneffectonthetensile strength.HarichandranandSelvakumarreportedthat parti-clesdisplayedanagglomerationwhentheB4Cratiowasover

6%withrespecttoweightandthatthisformationcausedthe strengthandductilityofthecompositematerialstodecline [27].

Aftertheextrusion,SEMimagesweretakenandEDS analy-seswereperformedofAl6061materialthatwasnotreinforced

(7)

Fig.7–SEMimage(a–b)EDSanalysisfromthe1starea(c)EDSanalysisfromthe2ndarea(d)of6B4C6SiCcomposite

material.

inthe directionofverticalextrusion and ofthe composite materialreinforcedwith6%B4C+6%SiC.ExaminingtheSEM

imageof the Al6061 material, weobserved that therewas scarcelyanyporosityinthestructure(Fig.4).Inaddition,alloy composition ratesin the structurewere also calculated by means ofelemental analysis. SEMimages and EDS results obtainedfrom 6%B4C+6%SiCcompositematerialareshown

inFig.7.

Elementary(EDS)analyzes wereperformed fromcertain regionsofthecompositematerial.InFig.7a,intheEDS anal-ysistakenfrom zone1,the highboroncontentandcarbon ratioindicatethepresenceofB4Cparticles.IntheEDSresults

obtainedfromzone2,itisunderstoodthatthisparticleisSiC becauseofhigh siliconand carboncontent.Examiningthe SEMimageinFig.7d,weobservedthatcavitiesare formed aroundtheB4Cparticles.Theseresultfromtheweak

wettabil-itybetweentheB4Cparticlesandthematrixphase.Itisknown

thatthereisaproblemofwettabilitybetweenaluminumand B4Creinforcementinliteratureresearches[28].

InFig.8,itisseenthatsomehardparticlesarecrackedor broken.Itisthoughtthatmicro-cracksorfracturesoccurinthe hardbrittleceramicparticlesthatmoveintothemoldcavity withthematrixmaterialduetohighdeformationandfriction duringextrusion.Inasimilarstudy,itwasstatedthatmacroor microcracksoccurinB4Cparticlesextrudedwithaluminum

matrix[29].

3.2. Fractographyoftensilespecimens

ThreetensiletestswereperformedforeachoftheAl6061 com-positematerials,whichcontained12%ceramicparticleswith

respecttoweight.Afterthetensiletests,fracturesurfacetests were conducted tocharacterize the fracture behaviors and the interfacebondsbetweenthe matrix andreinforcement materials. Toinvestigatethe microstructuresofthebroken surfaces,samplesweretakenfrom fullsectionsofthe frac-turedsurfacesandplacedintheSEMdevice.SEMimagesat differentmagniﬁcationsweretakenfromthebrokensurfaces ofnon-reinforcedAl6061,6%B4C,6%SiC,12%B4C,and12%SiC

compositematerials(Fig.9).

Theexcessiveductilitypreferredintheproductionof com-positematerialscausedmicro-poringonallthesurfacesofthe brokenmaterials,owingtotheAl6061matrix.Ahigherlevelof dimpleformationwasobservedonthebrokensurface,owing tothestructureofthenon-reinforcedAl6061material,which hasabehaviorthatismoreductilecomparedwithreinforced composites. Comparing the particle-reinforced composites, it wasobserved that dimple formationon the broken sur-faces decreased in parallel with the increase in B4C ratio.

ThisresultedfromthetrendoftheB4Cratio,whichincreases

brittlenessincompositematerials.Comparingthebroken sur-facesof12%B4Cand12%SiC,weobservedthat12%SiCcaused

theformationofmoredimples.Asaresult,the12%SiC com-positematerial,whichwasmoreductile inthetensile test, displayedgreaterstrength.

ItwasobservedthatB4Cparticlesonthebrokensurfaces

are debonded from the matrix. Due to the weak bonding betweenthematrixphaseandB4CparticlesinB4C-reinforced

compositematerials,thatis,duetoinsufﬁcientwetting,B4C

particlesareeasilydebondedfromthematrixatthemoment ofbreakageandremainedonbothsidesofthebroken sur-faces.InSiC-reinforcedcomposites,ontheotherhand,itwas

(8)

Fig.8– SEMimageof6B4C6SiCcompositematerial,X500(a),X2500(b).

Fig.9–SEMimageofthebrokensurfacesafterthetensiletest(a)Al6061(b)6B4C6SiC(c)12B4C(d)12SiC.

observedthat, thankstogoodbondingattheinterface,the SiCparticlesremainedembeddedinthematrixphaseatthe momentoftraction.

3.3. Effectofslidingdistanceandloadonvolumeloss ThevariationinvolumelossoftheHMMCsandunreinforced compositeAl6061asafunctionofloadandslidingdistanceare showninFig.10.Thevolumelossincreasedwiththeincrease inapplied load and weardistance inall samples.Canakci investigatedmicrostructureandabrasivewearbehaviorofB4C

particle reinforced 2014 Almatrix composites. The experi-mentalresultsshowedthatslidingtime(distance)affectsthe averagewearvolumelossofthecomposites.Thevolumeloss alsoincreaseswithincreasingslidingtime(distance)andwith decreasingparticlecontentofB4C.Hisresultsshowthegood

agreementwiththepresentstudy[30].Hardreinforcing parti-clesincreasethewearperformanceofAlMMCs[31].

Ascan beseen from Fig. 10, the volume lossofAl6061 waslowercomparedtothatintheHMMCs.Whilethe mini-mumvolumelosswasfoundtobe0.07mm3_from_the_12%B

4C

hybridcompositefora5Nloadanda100mslidingdistance, themaximumvolumelosswasfoundtobe3mm3_for_the

12%SiChybridcompositefora15Nloadanda300msliding distance.AsevidentfromFig.10,weightlossdecreasedwith

theincreaseinweightpercentofB4CintheHMMCs.TheB4C

reinforcementdecreasedthevolumelossmorethantheSiC reinforcementandhadeffectsthataremorebeneﬁcial.The 9%B4C+3%SiCsamplesexhibitedalowerweightlossthanthe

12%B4Csamples.The9%B4C+3%SiCsamplesshowthehighest

wearresistance.

3.4. Effectsofslidingdistanceandloadonthewear rate

Toinvestigatethe relationshipbetweenreinforcement con-tentofHMMCs,slidingdistance,andload,thewearrateswere calculated. Thewearrates of the unreinforcedand HMMC samplesaregivenasafunctionofslidingdistanceinFig.10.As canbeclearlyseenfromtheﬁgures,thewearratedecreases linearlywiththeincreaseinslidingdistance.Uthayakumarat al.InvestigatedwearperformanceofAl–SiC–B4Chybrid

com-positesunderdryslidingconditions.Theydeﬁnedthat,asa resultoflargescaleplasticdeformation,wearrateincrease withincreaseintheloadsapplied[32].Theresultsshowthe goodagreementwiththepresentstudy.Tangetal.[33]also deﬁnedthatAl–B4Ccompositesshowedhigherwearrateat

higherloads(65N).

Al6061 samples exhibit greater wearrates compared to thoseofHMMCsamples.The9%B4C+3%SiChybrid

(9)

compos-Fig.10–Variationinthevolumelossesandwearrateof(a)Al6061(b)12SiC,(c)3B4C9SiC,(d)6B4C6SiC,(e)9B4C3SiCand(f)

12B4Cwt.%Hybridcompositeasafunctionoftheslidingdistanceatdifferentappliedloads.

iteexhibitsthelowestwearrate.AsevidentfromFig.3,B4C

particleshavemorebeneﬁcialeffectsonthewearratethan SiCparticles.Theseresultscanbeattributedtothegreater hardnessoftheB4Cparticles.

AscanbeseenfromFig.10,themaximumwearratewas foundtobe6.6×10−13mm3_/m _for_the_12%SiC _hybrid

com-positefora15Nload and300mslidingdistance,whilethe minimumwearratewasfoundtobe1.4×10−13mm3_/m_for_the

9%B4C+3%SiChybridcompositefora5Nloadand100m

slid-ingdistance.Uthayakumaretal.[32]reportedthatB4Ceasily

createdaboronoxide(B2O3)layeronthesurfaceofasample.

Thislayerreducesthewearratesigniﬁcantly.

3.5. Effectsofslidingdistanceandloadonthefriction coefﬁcient

Thecoefficientoffrictionofthe unreinforcedsamplesand HMMCssampleswere measuredinorder todeterminethe wearbehavior.AsillustratedinFig.11,thecoefficientof fric-tiondecreasedwiththeincreaseinloadbutalsofluctuated duringsliding.Allsamplesdisplayedsimilartrendsforthe coefficient of friction during sliding. Previous studies [34], showed that alocalized abrasive zone formedby ahigher loadincreasedthecoefficientoffriction.Ghoshatal.studied thetribologicalcharacteristicsofAl-SiCMMC.Theyobserved thatfrictioncoefficientofcompositematerialsdecreasedwith increasinginappliedloads[35].

AscanbeseenfromFig.11,thecoefﬁcientoffriction var-ieddependingontheB4Creinforcementcontent.The12%B4C

samplesshowedthelowestcoefﬁcientoffrictionofthehybrid composites. Thecoefﬁcients offriction forAl6061,12%SiC, 3%B4C+9%SiC,6%B4C+6%SiC,9%B4C+3%SiC,and12%B4Cwere

foundtobe0.63,0.51,0,42,0.35,0.23,and0.29,respectively,for a15Nloadand300mslidingdistance.Ascanbeobservedfrom Fig.11,thecoefﬁcientoffrictiondecreaseswiththeincrease incontentofSiCandB4Cparticles.TheeffectsofB4Conthe

coefﬁcientoffrictioncanbeattributedtoaboronoxide(B2O3)

layerformingatthecontactzone.TheB4Cparticlesareeasily

pulledoutandreactwiththeenvironment,thuscreatingthe B2O3oxidelayer.

3.6. Characterizationofwearmechanismsbyanalysis ofwornsurfaces

The optimum wear resistance was achieved with the 9%B4C+3%SiCHMMCssamples.Therefore,thewornsurfaces

ofthe9%B4C+3%SiCsampleswereanalyzedthroughSEMin

ordertodeﬁnethewearmechanismsanditwasclearthatthe wearmechanismschangewiththewearconditions(i.e.,load andslidingdistance).Thewearmechanismsthatcanoccurin AlMMCsincludeadhesives,abrasives,delaminationand abra-sionwear[31].Abrasionwearappearsonthewornsurfacefor 5Natslidingdistancesof100mand300m(Fig.12).Deeper grovesappearforlongerslidingdistancesthanforshorter

(10)

slid-Fig.11–Variationinthefrictioncoefﬁcientof(a)Al6061(b)12SiC,(c)3B4C9SiC,(d)6B4C6SiC,(e)9B4C3SiCand(f)12B4Cwt.%

Hybridcompositeasafunctionoftheslidingdistanceatdifferentappliedloads.

ingdistances.Itcanbedeterminedfromthisthatthewear contactinterfacetemperatureincreasedwithincreasing slid-ingdistance[36].Wearcracksalsoappearinthewornsurface forlowerloads(Fig.12).AscanbeenfromFig.12,numerous groovesonthewornsurfacearealignedparalleltothesliding direction.

Deformation and delamination wear mechanisms are formedfor10Natslidingdistancesof100mand300m.The delaminationwearmechanismscanbeexplainedasbeingdue toaremovalofmaterial,becausecracksoccurwhere delami-nationoccurs[37].Workhardeningiscausedbydeformation

ofthematrix.Ahigherloadincreasesworkhardening, and asaresultcracksareformedinthematrixandreinforcement interface.Thecrackscausethedelaminationwear.Ascanbe seenfromFig.12,thedegreeofdelaminationwearontheworn surfaceincreaseswiththeincreaseinload.Deformation (plas-tic)wearisalsoshowninFig.12.Largerdeformationzones areseenforhigherloadsandslidingdistances(Fig.12).Fig.12 showsthatseveralwearmechanismsoccurredontheworn surfacefor10Natslidingdistancesof100mand300m.

EDSresultsofwornsurfacesfor150Nataslidingdistances of100and300mare giveninFig.13inordertoreveal the

(11)

Fig.12–SEMimagesofthewornsurfacemorphologiesofthe9B4C3SiCsamples(a)5N-100m,(b)5N-300,(c)10N-100m,

(d)10N-300m,(e)130N-100m,(f)30N-300m.

Fig.13–SEMimagesofwornsurface(a)9B4C3SiC,(b)12B4C,(c)EDSanalysisfromthe9B4C3SiC(d)EDSanalysisfrom12B4C.

effectsofSiCandB4Conthewornsurfaces.Allpeaksofthe

aluminumalloyandSiCandB4Creinforcementparticlesare

observed.Thischaracterizationofthewornsurfacesreveals thatSiCparticleshaveabetterinterfacebetweenthematrix andparticlescomparedtoB4Cparticles.SiCparticlesare

bro-kenduringthewearingprocess,whileB4Cparticlesarepulled

out.Thehigherwearresistanceof9%B4C+3%SiCcompared

to 12%B4C can beattributed tothis behavior. SiC particles

alsodisplayedgoodbondingandarenotpulledoutfromthe matrix.Uthayakumaretal.foundthatSiCcanbecometrapped betweentheslidingsurfacesorembeddedintothesoft alu-minummatrixandthusincreasesthewearresistance[33].

(12)

Fig.14–Volumelossmapof9B4C3SiCsamples.

3.7. Volumelossmap

Fig.14showsavolumelossmapforthe9%B4C+3%SiCHMMCs

samples under various wear conditions. Each contour on Fig.14marksthevolumelossfordifferentsliding distances andloads.Thecontourvolume lossmapwas drawnusing ORIGINsoftwareforvolumelossdata.Fig.14givesadetailed illustrationofhowvolumelosschangeswithdifferentwear conditions.Thevolumelossisthelowestatalowerloadand shorterslidingdistanceandthehighestatahigherloadand longerslidingdistance.

3.8. Mapofwearmechanisms

Amapofthewearmechanismsofthe9%B4C+3%SiCHMMCs

samplesaregiveninFig.15fordifferentwearconditions.As canbeclearlyseen,thewearconditionsdirectlyinﬂuencethe wearmechanisms.Whichwearmechanismsdominateatthe

anismsplayanimportantroleintheseverewearregimeand thedeformationwearmechanismmostlyoccursinthe ultra-severewearregime.

4. Summary

and

conclusions

In this study, a non-reinforced Al6061 alloy and B4

C/SiC-reinforced compositematerialswere produced successfully usingahotextrusiontechnique.Thepropertiesofthe pro-duced materials,such asthe density, hardness,transverse rupturestrength,tensilestrength,andwear,wereexamined. Thestudyyieldedthefollowingﬁndings:

1. Itisproducedwithhighdensitymaterialsbyhot extru-sion technique. The average densities of cold pressed andextrudedcompositesrespectivelywere89and99%, respectively.Whilethehighestdensitywasobservedin theextrudedAl6061alloy(99.74%),compositematerials reinforcedwithextruded12%B4Chadthelowestdensity

(99.02%).

(13)

4. Determiningthehardnessvaluesofthecomposites pro-duced,the studyfoundthatreinforcedcompositeshad higher hardness values compared with the reinforced Al6061alloy.WhiletheAl6061alloyhadanaverage hard-nessvalueof50HB,the12%B4Ccompositedisplayedthe

highestvalueof76HB.

5. Investigatingthetransverserupturestrengthvalues,we foundthatwhile12%SiC-reinforcedcompositesshowed thehighesttransverserupturestrengthwith402MPa,the 12%B4Ccomposite,whichhadthehighesthardnessvalue,

hadthelowesttransverserupturestrengthwith358MPa. Inthe B4Cand SiCcomposites,onthe otherhand,the

transversestrengthvaluesdisplayedadecreaseinparallel withtheincreaseinB4Cratio.

6. Al6061alloyhasalowertensilestrength(174MPa)than thoseofthecomposites.Thehighesttensilestrengthwas achievedin12%SiCreinforcedcomposites(185.1MPa).In B4C/SiCcomposites,somedecreaseintensilestrength

wasobservedduetoB4Cratio.

7. Theminimumvolumelosswasfoundtobe0.07mm3_for

the12%B4Chybridcompositefora5Nloadand100m

slid-ingdistance,whilethemaximumvolumelosswasfound tobe3mm3_for_the_12%SiC_hybrid_composite_for_a₁₅_N

loadand300mslidingdistance.

8. Abrasion, deformation, anddelamination wear mecha-nismsoccurredonthesurfacesdependingonthewear conditions.Thewearmechanismscanbedeterminedby controllingthewearconditionsforHMMCs.

9. The highest wear resistance was obtained for the 9%B4C+3%SiCsamplesbecauseofthehardnessofB4Cand

thegoodadherencepropertiesofthematrixandSiC. 10. Thecoefﬁcientoffrictionvarieswiththereinforcement

typeandcontent.Thelowestcoefﬁcientoffrictionwas obtainedforthe12%B4Csamples.

Acknowledgments

ThisworkwasﬁnanciallysupportedbytheGaziUniversity Sci-entiﬁcResearchProjectsCoordinationUnit(07/2016-03).The author wish tothankthe HacettepeUniversity Technology TransferCenterUnit.

oxidesbasedhybridAMCsreinforcedwithSiC/Al2O3: Mechanical&metallurgicalcharacterization.JMaterRes Technol2019,http://dx.doi.org/10.1016/j.jmrt.2019.01.013. [7]GodeC.MechanicalpropertiesofhotpressedSiCpand

B4Cp/Alumix123compositesalloyedwithminorZr.Compos PartBEng2013,

http://dx.doi.org/10.1016/j.compositesb.2013.04.068. [8]HeknerB,MyalskiJ,ValleN,Botor-ProbierzA,Sopicka-Lizer

M,WieczorekJ.FrictionandwearbehaviorofAl-SiC(n) hybridcompositeswithcarbonaddition.ComposPartBEng 2017;108:291–300,

http://dx.doi.org/10.1016/j.compositesb.2016.09.103. [9]SinghJ,ChauhanA.Characterizationofhybridaluminum

matrixcompositesforadvancedapplications—areview.J MaterResTechnol2016;5:159–69,

http://dx.doi.org/10.1016/j.jmrt.2015.05.004.

[10]SaﬁuddinM,JumaatZ,SalamMA,HashimR.Utilizationof solidwastesinconstructionmaterials,vol.5;2010.

[11]AlanemeKK,AdewaleTM,OlubambiPA.Corrosionandwear behaviourofAl-Mg-Sialloymatrixhybridcomposites reinforcedwithricehuskashandsiliconcarbide.JMaterRes Technol2014;3:9–16,

http://dx.doi.org/10.1016/j.jmrt.2013.10.008. [12]RamachandraM,RadhakrishnaK.

Synthesis-microstructure-mechanicalproperties-wearand corrosionbehaviorofanAl-Si(12%)-Flyashmetalmatrix composite.JMaterSci2005;40:5989–97,

http://dx.doi.org/10.1007/s10853-005-1303-6.

[13]SinghJ,ChauhanA.Characterizationofhybridaluminum matrixcompositesforadvancedapplications–areview.J MaterResTechnol2016;5:159–69,

http://dx.doi.org/10.1016/j.jmrt.2015.05.004.

[14]RamanathanA,KrishnanPK,MuralirajaR.Areviewonthe productionofmetalmatrixcompositesthroughstircasting —Furnacedesign,properties,challenges,andresearch opportunities.JManufProcess2019;42:213–45, http://dx.doi.org/10.1016/j.jmapro.2019.04.017. [15]BasavarajappaPM,ParashivamurthyKI.Synthesisand

tribologicalcharacterizationofin-situpreparedAl-TiC composites.AmJMaterSci2017;2017:108–11, http://dx.doi.org/10.5923/j.materials.20170704.08.

[16]MohapatraS,ChaubeyAK,MishraDK,SinghSK.Fabrication ofAl-TiCcompositesbyhotconsolidationtechnique:its microstructureandmechanicalproperties.JMaterRes Technol2016;5:117–22,

http://dx.doi.org/10.1016/j.jmrt.2015.07.001. [17]AlamMT,AnsariAH.X-raydiffractionanalysisand

microstructuralexaminationofAl-Siccompositefabricated bystircastingtechnique.IntJSciTechnolManag

2015:941–55.

[18]RaoJB,KushD,BhargavaN.Productionandcharacterization ofnanostructuredsiliconcarbidebyhighenergyball

(14)

MatrixCompositesbyTwoStepStirCastingProcess.LatAmJ SolidsStruct2016;7075:243–55.

[22]MonikandanVV,JosephMA,RajendrakumarPK.Drysliding wearstudiesofaluminummatrixhybridcomposites.Resour Technol2016;2:S12–24,

http://dx.doi.org/10.1016/j.refﬁt.2016.10.002.

[23]XuY,SunY,DaiX,LiaoB,ZhouS,ChenD.Microstructureand magneticpropertiesofamorphous/nanocrystallineTi50Fe50 alloyspreparedbymechanicalalloying.JMaterResTechnol 2019;8:2486–93,http://dx.doi.org/10.1016/j.jmrt.2019.02.007. [24]ManiammalK,MadhuG,BijuV.X-raydiffractionlineproﬁle

analysisofnanostructurednickeloxide:Shapefactorand convolutionofcrystallitesizeandmicrostraincontributions. PhysELow-DimensionalSystNanostructures

2017;85:214–22,http://dx.doi.org/10.1016/j.physe.2016.08.035. [25]ZhangP,LiY,WangW,GaoZ,WangB.Thedesign,fabrication

andpropertiesofB4C/Alneutronabsorbers.JNuclMater 2013,http://dx.doi.org/10.1016/j.jnucmat.2013.02.050. [26]ImranM,KhanARA.CharacterizationofAl-7075metal

matrixcomposites:Areview.JMaterResTechnol

2019;8:3347–56,http://dx.doi.org/10.1016/j.jmrt.2017.10.012. [27]HarichandranR,SelvakumarN.Effectofnano/microB4C

particlesonthemechanicalpropertiesofaluminiummetal matrixcompositesfabricatedbyultrasonic

cavitation-assistedsolidiﬁcationprocess.ArchCivMechEng 2016;16:147–58,http://dx.doi.org/10.1016/j.acme.2015.07.001. [28]BaradeswaranA,ElayaPerumalA.InﬂuenceofB4Conthe

tribologicalandmechanicalpropertiesofAl7075-B4C composites.ComposPartBEng2013,

http://dx.doi.org/10.1016/j.compositesb.2013.05.012.

[32]UthayakumarM,AravindanS,RajkumarK.Wear performanceofAl-SiC-B4Chybridcompositesunderdry slidingconditions.MaterDes2013,

http://dx.doi.org/10.1016/j.matdes.2012.11.059.

[33]TangF,WuX,GeS,YeJ,ZhuH,HagiwaraM,etal.Drysliding frictionandwearpropertiesofB4Cparticulate-reinforced Al-5083matrixcomposites.Wear2008,

http://dx.doi.org/10.1016/j.wear.2007.04.006.

[34]RavindranP,ManisekarK,NarayanasamyR,Narayanasamy P.Tribologicalbehaviourofpowdermetallurgy-processed aluminiumhybridcompositeswiththeadditionofgraphite solidlubricant.CeramInt2013,

http://dx.doi.org/10.1016/j.ceramint.2012.07.041.

[35]GhoshS,SahooP,SutradharG.WearbehaviourofAl-SiCp metalmatrixcompositesandoptimizationusingtaguchi methodandgreyrelationalanalysis,2012;2012:1085–1094. https://doi.org/10.4236/jmmce.2012.1111116.

[36]GåårdA,HallbäckN,KrakhmalevP,BergströmJ.Temperature effectsonadhesivewearindryslidingcontacts.Wear 2010;268:968–75,http://dx.doi.org/10.1016/j.wear.2009.12.007. [37]WearbehaviourandmicrostructuralchangesofSiCw-Al

compositeunderunlubricatedslidingfriction.Wear 1995;184:187–92,

http://dx.doi.org/10.1016/0043-1648(94)06577-2.

[38]AlpasAT,ZhangJ.Effectofmicrostructure(particulatesize andvolumefraction)andcounterfacematerialonthesliding wearresistanceofparticulate-reinforcedaluminummatrix composites.MetallMaterTransA1994;25:969–83,