Fabrication of Al5083/B4C surface composite by friction stir processing and its tribological characterization

w w w . j m r t . c o m . b r

Availableonlineatwww.sciencedirect.com

Original

Article

Fabrication

of

Al5083/B

4

C

surface

composite

by

friction

stir

processing

and

its

tribological

characterization

Narayana

Yuvaraj

a

_,

_Sivanandam

_Aravindan

b,∗

_,

_Vipin

a

a_{DepartmentofMechanicalEngineering,DelhiTechnologicalUniversity,Delhi,India} b_{DepartmentofMechanicalEngineering,IndianInstituteofTechnology,Delhi,India}

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received13October2014 Accepted8February2015 Availableonline18March2015

Keywords:

Frictionstirprocessing Boroncarbide(B4C)

Numberofpasses Hardness Wear

a

b

s

t

r

a

c

t

Improvedsurfacepropertieswiththeretainmentofbulkpropertiesarenecessaryfora com-ponentforenhancedwearcharacteristics.Frictionstirprocessing(FSP)isusedtoproduce suchsurfacecomposites.Fabricationof5083aluminumalloywithreinforcedlayersofboron carbide(B4C)throughFSPwascarriedout.MicroandnanosizedB4Cparticleswereused

asreinforcements.Thefrictionprocessedsurfacecompositelayerwasanalyzedthrough opticalandscanningelectronmicroscopicalstudies.Thenumberofpassesandthesizeof reinforcementplayavitalroleinthedevelopmentofsurfacecompositesbyFSP.Mechanical propertiesofthefrictionstirprocessedsurfacecompositeswereevaluatedthroughmicro hardnessanduniversaltensiletests.Theresultswerecomparedwiththepropertiesofthe basemetal.Theroleofreinforcementandnumberofpassesonpropertieswerealso eval-uated.Tribologicalperformanceofthesurfacecompositesistestedthroughpinondisk test.Thesurfacecompositelayerresultedinthreepasseswithnanoparticlereinforcement exhibitedbetterpropertiesinhardness,tensilebehaviorandwearresistancecomparedto thebehaviorofthebasemetal.

©2015BrazilianMetallurgical,MaterialsandMiningAssociation.PublishedbyElsevier EditoraLtda.Allrightsreserved.

1.

Introduction

The aluminum based metal matrix composites provide excellent specific strength, stiffness, high hardness, wear resistance, stability at high elevated temperature [1] with additional advantages of three dimensional isotropy and affordability[2].TheAl–B4Ccompositesareusedinthe

bicy-cleframe, bullet proofvests, armor tanks,containment of

∗ _{Correspondingauthor.}

E-mail:[email protected](S.Aravindan).

nuclearwaste,neutronabsorberinnuclearpowerplant, trans-portationapplications,etc.owingtotheirhighhardness,low density and excellentthermal and chemical stability [2–4]. Al–B4C compositesare fabricatedby variousresearchersin

thepastfewyearsbystircasting[5–7],casting[8–10],squeeze casting[11]andmechanicalalloying[12].

However, a surface property of the material is very importanttoachievelongerlifeofmechanicalcomponents. Dispersionofthenanoreinforcementsinthesurfacetohave

http://dx.doi.org/10.1016/j.jmrt.2015.02.006

a

DTU_S3700 20.0kV 16.0mm x1.70k SE 30.0um 10:26:18 AM4/3/2014 spot 4.5 HV 10.0 kV mag 60 000 x WD 10.0 mm 500 nm Quanta 3D FEG

b

Fig.1–SEMmicrographsofas-received(a)B4Cmicroparticles,(b)B4Cnanoparticles.

a

b

5

∅18

M6x1.0

All dimensions are in mm

Fig.2–MacrographofFSPtool.

auniformlayerisadifficulttask.Existingprocessing tech-niques for processing of surface composites are based on liquid phase processingat high temperature suchas laser melttreatment,electronbeamirradiationandplasma

spray-ing[13–15].Inthesecases,therewillbeaninterfacialreaction

betweenthe matrixand reinforcement,which leadstothe formationofdetrimentalphases.Theaboveproblemscanbe eliminatedbyprocessingitbelowthe meltingpointof sub-strate.Therecentnewsurfacemodifyingtechniquenamed FrictionStirProcessing(FSP)[16]isdevelopedbyutilizingthe principleofthefrictionstirwelding(FSW).FSWwasinvented

FSP Tool

200

Stirring zone

All dimensions are in mm Pin Shoulder .5083 Al alloy plate

8 75

Groove filled with boron carbide particles

Fig.3–SchematicofFSPexperiment.

bytheweldingInstituteUKin1991[17].FSPisasolidstate processingtechniqueforproducingathickcompositelayer; the layer thickness can range from hundreds of microme-terstoseveralmillimeters.FSPisalsousefultoobtainafine grainedmicrostructureandtoremovethecastdefectswith improvedmechanicalpropertiesandwearresistance[18–20]. The successful fabrication of aluminum based metal matrix compositesreinforcedwithparticulatessuchasSiC

All dimensions are in mm B A C 8 75 200

Fig.4–Schematicillustrationoftheprocedureforcutting (A)tensilespecimen,(B)pinspecimenforweartest,(C)

Table1–Chemicalcompositionofbasematerial.

Elements Mg Cr Mn Fe Zn Si Ti Cu Ni Al

%wt 4.162 0.064 0.554 0.191 0.029 0.230 0.049 0.051 0.023 Bal

All dimensions are in mm 70

20 4

R12.5

6

12

Fig.5–Theconfigurationofthetensilespecimen.

a

b

100 μm 100 μm 10 _μm 10 _μm 10 μm 10 μm

c

d

e

f

Fig.6–Opticalmicrographsoftransversecross-sectionaloftheFSPzonespecimens(a)basematerial,(b)withoutparticle onepassstirzone,(c)B4Cmicrosizedparticleonepass,(d)B4Cmicrosizedparticlethreepass,(e)B4Cnanosizedparticle onepass,(f)B4Cnanosizedparticlethreepass.

[21–24],Al2O3[25–27],Si3N4[28],B4C[29,30],ZrO2[31]andTiO2

[32]werereported.However,noliteratureisavailableonFSPof 5083aluminumalloywithB4Cnanocomposites.Thepresent

workaimstofabricate5083aluminumalloysurfacecomposite

byFSPwiththereinforcementofB4Cmicroandnanoparticles.

Theeffectsofnumberofpassesonthemicrostructure,micro hardness, tensile strength andwear behaviorwere investi-gated.

Table2–MechanicalpropertiesofFSPcomposites.

Specimen Grainsize(␮m) Microhardness(Hv) Ultimatestress(MPa) Total%elongation

Basematerial 49.85 82.6 310 26.8

Withoutparticleonepass 18.46 107.2 331 30.0

MicrosizedB4Cparticleonepass 8.16 112.1 246 15.4

MicrosizedB4Cparticlethreepass 6.52 116.4 323 11.0

NanosizedB4Cparticleonepass 7.64 119.6 334 16.6

NanosizedB4Cparticlethreepass 3.98 124.8 360 14.9

10 20 30 40 50 2_θ (degree) A1 B4C Intensity (a.u) 60 70 80

Fig.7–XRDofthespecimensFSPednanosizedB4C particlethreepasses.

2.

Materials

and

methods

Alalloyof5083-Orolledplate of8mmthicknesswasused. ThechemicalcompositionispresentedinTable1.Themicron sizedB4Cparticles withapurityof99%havinganaverage

particle size of20␮m and nanosize B4C particle of99.5%

puritywiththemeanparticlesizeof30–60nmwereusedas reinforcementmaterials.TheSEMmicrographsofthe parti-clesare showninFig.1.Thesemicrographsrevealthe size

Nano particle three pass Nano particle one pass Micro particle three pass Micro particle one pass Without particle one pass Base material

Distance from center of stir zone (mm)

Microhardness (Hv) –10 80 80 100 110 120 130 –8 –6 –4 –2 0 2 4 6 8 10

Fig.9–MicrohardnessvalueFSPedspecimenswithand

withoutparticlesontheSCL.

andmorphologyofmicroandnanolevelparticles.Thetool madeofH-13toolsteelhardenedto55HRCwithashoulderof 18mmdiameterwiththreadedpindiameterofM6×1.0ofpin lengthof5mmwasusedforFSP.Agroove(1mmwidthand 3mmdepth)wasmadeinthemiddleoftheworkpieceand thegroovewasthenfilledwiththereinforcements.A probe-lessFSPtoolwithshoulderonlywasinitiallyusedtoprevent theescapeoftheparticlesfromtheFSPzone.Thenthe sam-plesweresubjectedtovariousnumbersofpassesfromoneto three.

A1

B

10/13/2014 10:31:38 AM spot 6.5 HV 10.0kV mag 60 x WD 10.0 mm 1 mm Quanta 3D FEG

C

M

2

Nano particle three pass Nano particle one pass Micro particle three pass Micro particle one pass Without particle one pass

Distance from the top surface (mm)

Average hardness of base material

Microhardness (Hv) 90 85 80 95 105 100 115 110 125 120 130 0 1 2 3 4 5 6

Fig.10–MicrohardnessprofileofFSPedspecimenswith andwithoutparticlesofthecrosssectionregion(asa functionofdepth).

Anindigenously developedFSWmachine (11kW, 40kN) wasusedtofabricatethesurfacecompositelayer.The spec-imenswereclampedonthehydraulicfixturewithmildsteel backingplate.Theconstantrotationalspeedandtransverse speed were fixed at1000rpm and 25mm/min respectively afternumber oftrials. The advancing and retreating sides oftheparentmetalswerechangedaftereachFSPpass.For every pass, the specimenwas allowedto becooled tothe roomtemperatureandalltheexperimentswerecarriedout atroomtemperature.Fig.2(a)showsthephotographofthe threadedtoolusedforthestudyandFig.2(b)showsits dimen-sions.Fig. 3showsthe schematicofFSPexperiment. After FSP,thesampleswerecutinthetransversedirectionand pol-ishedwithdifferentgradesofemerysheetsandthesamples wereanalyzedthroughopticalmicroscope.Amodified Poul-ton’sreagent(30mlHCl,40mlHNO3,2.5mlHF,12gCrO3,and

42.5mlH2O) wasused tostudy microstructureofthe base

metalandthestirzoneofthesurfacecompositelayer(SCL). Scanningelectronmicroscope(SEM)(HitachiS3700)wasused toexamine the distributionofthe reinforcement particles. XRD(BRUKERD8ADVANCE)wasusedtoidentifythepresence

Nano particle three pass Nano particle one pass Micro particle three pass Micro particle one pass Without particle one pass Base material Strain (%) Stress (mpa) 100 50 0 150 200 300 250 350 400 0 5 4 1 2 3 4 5 6 6 5 2 1 3 10 15 20 25 30

Fig.12–Stress–straincurvesforbasemetalandspecimens FSPedwithandwithoutparticleswithdifferentpasses.

ofphasesintheStirzoneofSCL.TheVickersmicrohardness (FutureTechJapan)valuesoftheFSPedregionswasmeasured along and perpendicular (cross section) to the processing directionusingaloadof100gwithdwelltimeof10s.The ten-silepropertiesoftheFSPedspecimenswereexaminedusing computercontrolleduniversaltestingmachine(TiniusOlsen H50KS)ataconstantcrossheadspeedof1mm/mininroom temperature.Thelongitudinaltensilespecimenspreparedon the middleoftheFSPstir zonebywireEDMasper ASTM: E8/E8M-011 standard.Figs.4and5show thesizeand con-figurationofthespecimensforthetests.Thewearbehavior oftheSCLwasstudiedthroughpinondisktribometer(make DUCOM)inroomtemperaturecondition.Weartestspecimens of10mmdiameterwerecutfromthemiddleofstirredzone ofFSPedsurfacebywireEDM.Tribotestswereconductedas perASTMG99-04standard.Thecounterpartdiscsweremade ofEN-24steelhardenedto58HRCandthesurfaceroughness (Ra)of0.2␮m.Aconstanttrackdiameter100mmwasusedin allthetests.Beforethetest,thesurfaceofeachpinwas pol-ishedon1200gritemerypaper.Theweartestwasconducted

a

d

b

DTU_S3700 15.0kV 17.7mm x 900 SE 50.0umDTU_S3700 15.0kV 18.3mm x 800 SE 50.0um

DTU_S3700 15.0kV 18.6mm x 800 SE 50.0umDTU_S3700 15.0kV 17.8mm x 650 SE 50.0um

DTU_S3700 15.0kV 17.6mm x 850 SE 50.0umTDTU_S3700 15.0kV 17.4mm x 1.00K SE 50.0um

e

c

f

Fig.13–SEMfractographsof(a)basematerial,(b)specimenFSPedwithoutparticleonepass,(c)specimenFSPedwithB4C

microparticleonepass,(d)specimenFSPedwithB4Cmicroparticlethreepasses,(e)specimenFSPedwithB4Cnanoparticle

onepass,(f)SpecimenFSPedwithB4Cnanoparticlethreepasses.

ataslidingvelocityof2m/s,normalforceof30Nand slid-ingdistanceof3000m.Atevery 500minterval thesamples were cleanedwithacetone and weighed toan accuracyof 0.001mgby electronic weighing balance. Theapplied load as well as the sliding speed were fixed in order to com-pare the active wear mechanisms in similar conditions. Thefriction coefficientbetweenthepin specimenand disc was determined by measuring the frictional force with a stresssensoratthedistanceof3000mwithoutstoppingof the disc rotation at the same sliding velocity and normal force.

Tounderstandthewearmechanismsthewornsurfacesof theSCL and basemetalwere examined bySEM. Thewear behaviorofsurfacecompositelayerprocessedatsingleand multi(three)passeswithmicroandnanoparticleswas com-paredwiththewearbehaviorofbasemetal.FSPedsurfaces withoutmicro/nanoreinforcementwerealsostudiedtohave betterunderstanding.

3.

Results

and

discussion

3.1. Microstructuralanalysis

MicroscopicobservationoftheSCLisshowninFig.6.TheB4C

particleswerefoundtobeclusteredinthestirzoneaftereach FSPpass.Thereinforcementparticlesarestrengthening pre-cipitatesofAl5083alloythatdispersedintheAlmatrix.The finergrainswerefoundintheSCLcomparedtotheasreceived Alsubstrate,duetosevereplasticdeformationanddynamic recrystallization. Earlier reportsalsostated that the refine-ment of grainsand uniform distribution ofparticles could beobtainedbyFSP[33].Withtheincreaseinthenumberof FSPpassespowderdistributionbecomesmorehomogeneous andreducedclusteringofreinforcementparticlesisobserved. Gooddispersionofreinforcementoccursinthematrixandthe sizeofthegrainisalsoreducing.TypicalXRDprofileofnano

Base material

Without particle one pass Micro particle one pass Micro particle three pass Nano particlel one pass Nano particle three pass

Base material

Without particle one pass Micro particle one pass Micro particle three pass Nano particlel one pass Nano particle three pass 0.006

b

c

a

0.005 0.004 0.003 0.002 0.001 500 1000 1500 Sliding distance (m) Microhardness (Hv) W ear r ate (mg/m) W e ight loss (mg) W ear r ate (mg/m) Sliding distance (m) 2000 2500 140 0.006 0.0055 0.005 0.0045 0.004 0.0035 0.003 0.0025 120 120 120 120 40 20 0 Base material Without particle one pass B4C micro particle one pass B4C micro particle three pass

Microhardness Wear rate B4C nano particle one pass B4C nano particle three pass 3000 0 0 2 4 6 5 10 12 14 16 18 500 1000 1500 2000 2500 3000

Fig.14–(a)VariationofweightlosswiththeslidingdistanceforbasemetalandspecimensFSPedwithandwithoutmicro andnanosizedB4Cparticles.(b)VariationsofwearratewiththeslidingdistanceforbasemetalandspecimensFSPedwith

andwithoutB4CmicroandnanosizedB4Cparticles.(c)Changeinwearratevsmicrohardness.

B4Creinforcedaluminumalloyspecimensubjectedtothree

stirpassesisshowninFig.7.Theclearpeaksofaluminum andmarginalpeaksofB4Careobservedinthefigure.Fig.8

showstheSEMmicrographofcrosssectionofthreepassnano FSPedspecimenwithelementalcomposition.

3.2. Hardness

Thehardnessofbasematerialwas 82Hv.For experimental purpose,theaverageofthreehardnessvalueswastakenin allthesamples.Fig.9showthehardnessprofileofspecimens FSPedwithoutparticleonepass,withmicroandnanosized B4Cparticlesonepassandthreepasses.Theobtaineddata

iscompared withthe base material.Asadi et al. [34] have reportedthathardnessoftheFSPedAZ91/SiCnanocomposite isobservedtobeincreasedduetouniformdispersionofSiC particlesandrefinementofthegrainsizeofthebasematerial. Shamsipuretal.[35]havereportedthatthehardnessvalue couldbeincreasedby6.4timesforFSPedTi/TiN composite

surfacelayerincomparewithbasematerialduetothe uni-formdispersionofreinforcements.Morisadaetal.[36]have revealedthatFSPednanostructuredtoolsteelexhibitedmuch higher hardness in compared to base material. Faraji and Asadi[37]reportedthattheincreasednumberofpassesFSPin AZ91/Aluminananocompositethehardnessisobservedtobe higherthanthatofsinglepass.Thesecondpasshomogenizes theparticledistribution,decreasesthegrainsizeandproduces theuniformhardnessprofile.AccordingtotheHall–Petch rela-tionship,decreaseingrainsizeincreasestheyieldstrength, whichinturnincreasesthehardnessvaluealso.Dolatkhah etal.[22]haveachievedmaximumof116HvhardenedinFSP of5052Alwith50nmSiCparticlesduetoseveregrain reduc-tion.Shamsipuretal.[38]reportedthatmicrohardnessvalue ofTi/SiCnano surfacecomposite layeris3.3times greater thanthatofasreceivedtitaniumsubstrateduetouniform dis-persionofnanosizedreinforcementparticlesafterfourFSP passes. Zahmatkeshand Enayati [39]have achievedhigher hardnessvalueinthestirzoneofFSPinAl2024withAl2O3

DTU_S3700 15.0kV 17.1mm x 47 SE

a

b

c

g

h

i

1.00mm DTU_S3700 15.0kV 17.1mm x 2.70k SE 20.0um DTU_S3700 15.0kV 38.6mm x 40 SE 1.00mm DTU_S3700 15.0kV 26.4mm x 37 SE 1.00mm DTU_S3700 15.0kV 26.0mm x 2.10k SE 20.0um DTU_S3700 15.0kV 26.4mm x 2.70k SE 20.0um

Fig.15–SEMmicrographofthewornouttrackof(a)basematerial,(b)specimenFSPedwithoutparticleonepass,(c) specimenB4Cmicroparticleonepass,and(g),(h),(i)arehighmagnificationviewof(a),(b)and(c)respectively.

nanoparticlesthanthatofasreceivedmaterialdueto uni-formdispersion ofAl2O3 particlesinAlmatrix.Raaftetal.

[19]havereportedthatmicrohardnessvalueofA390/Al2O3and

A390/graphitesurfacecompositesexhibitedhigherhardness thanthe hardnessofasreceivedmaterial.Thehardnessis increasedduetograinrefinementoftheparticlesandhigher hardnessofreinforcementparticles. Shafiei-Zarghani etal.

[26]reportedthat thereisathreefoldincrease inhardness withpassesofFSP6082/Al2O3nanoreinforcementsandthe

dispersionofnano-sizeAl2O3inuniformmannerinthe Al

matrix.Increaseinthenumberofpassesofmanycomposite systems[36–40]hasprovedtheuniformityindistributionin hardness.

Thesurfacecompositelayerwithnanoparticlethreepass exhibitedhigherhardnesscomparedtonanoparticlesingle pass.ThehardnessoftheSCLdependsuponfinegrainsize ofAlmatrix,finedispersionofreinforcingparticles(B4C)in

aluminummatrixandquenchhardeningeffectdueto differ-enceinthermalcontractioncoefficientofaluminummatrix

andB4Creinforcingparticles[40].Theabovementioned

lit-eraturesupportsthefindingofincreasedhardnessofFSPed surfaces.TheAl5083/B4CnanoFSPsurfacecomposites

exhib-itedhigherhardnesswhencomparedwiththeFSPofmicro reinforcementparticles.Forexample,theAl5083/B4CnanoFSP

threepassandAl5083/B4Cmicrothreepasssurface

compos-itesexhibitedhardnessof134.8Hvand116.4Hvrespectively. ThedetailedhardnessvaluesarepresentedinTable2.

Fig. 10 shows the cross section (depth profile) of the microhardness from processed region to the unprocessed region.Basematerialhardnessisgiveninthefigure.TheFSP processedwithnanoparticlethreepasssurfaceexhibited60% increaseinhardness.Thisincreaseinhardnessisattributed todefectsclosurebyfrictionstirprocessand refinementof grains.Microparticledistributionfurtherincreasesits hard-nessandnanoparticlereinforcementimprovesthehardness. Furtherimprovementinhardnessbynumberofpassesis cer-tainlyattributedtoseveredeformationoftheparentmaterial, finergrainstructureanduniformityinparticledistribution.

DTU_S3700 15.0kV 27.4mm x 47 SE

d

e

f

j

k

l

1.00mm DTU_S3700 15.0kV 27.4mm x 2.10k SE 20.0um

DTU_S3700 15.0kV 27.7mm x 55 SE 1.00mm DTU_S3700 15.0kV 26.4mm x 2.50k SE 20.0um

DTU_S3700 15.0kV 26.3mm x 50 SE 1.00mm DTU_S3700 15.0kV 26.3mm x 2.30k SE 20.0um

Fig.16–SEMmicrographofthewornouttrackof(d)specimenFSPedB4Cmicroparticlethreepass,(e)specimenFSPedB4C

nanosizedparticleonepass,(f)specimenB4Cnanosizedparticlethreepassand(j),(k),(l)arehighmagnificationviewof

(d),(e)and(f)respectively.

3.3. Effectonthenumberofpasses

The number of FSP passes reduces the clustering effect, increasingtheuniformityofdistributionofparticles,which inturnresultsinimprovementofmechanicalandwear resis-tance properties. Thisobservation inmicro and nano B4C

reinforcement is supported by literature in various other materialsystems. Mahmoud [41] studiedthat FSPof A390 Alalloywiththreepassesandfoundthatthehardnessand wearresistanceoftheprocessedsurfacelayerwasimproved and the coefficient offriction was observed to be slightly reduced when compared with the un processed material. Shafiei-Zarghani et al. [42] have reported that nano size aluminaparticlesaremoreuniformlydistributedinthe alu-minummatrixduetoincreasingthenumberofFSPpasses. Alumina clusters were rarely reported. Increasing the FSP passesproducesthebetterdistributionofSiCandAl2O3nano

particles in the AZ91 matrix [43]. The hardness, strength,

elongation and wearresistance ofthe composite layer are reported tobe improved. Aftertwopasses, the nano sized Al2O3particlesaredispersedinauniformmannerintheAl

matrix.Orowanstrengtheningcanbeverysignificantinthe composites, thenanoparticles are welldistributed inintra granularlyandintergranularly.Theclustersizeisreducedand theintegrityintheparticle/matrixinterfacecanbeimproved byincreasingthenumberofpasses.

3.4. Mechanicalproperties

Fig. 11(a) and (b) shows the tensile specimens before and aftertestingandFig.12showstheresultforthebase mate-rial,andthe processedspecimensofmicroand nanosized B4Cparticleswithoneandthreepasses.Themaximum

ten-sile strengthwasachievedinthenanoparticleswiththree passes.Mechanicalpropertiesmainlydependonthefinegrain sizeanddislocationstrengthening.Restrictionofmovement

ofgrainboundariesisalsoinfluencingthetensileproperties ofthestirredzonematerial.Grainrefinementisthe impor-tantparametertodecidethesuperplasticbehaviorofmetal

[44].FSPAlalloysformsequiaxedfinegrainsduetostirring thematerialandtheyexhibitexcellentgrainrefinement.Fine grainsizeofnanosizedFSPcompositesleadstoabetter ten-silepropertiesafterthenumberofpasses.Zohooretal.[45]

have reported that there isan increase in the strength of theAlalloycompositewiththenumberofpasseswiththe FSPeffectsongrainrefinementandparticlereinforcementon theAlalloycomposite.FSPedAl–TiCinsitucompositeswith twopassesspecimenexhibitedthesignificantimprovementof tensilepropertiesduetohomogenization,refinementofgrain sizeandeliminationofcastingdefects[46].

Fig.13showsthetensilefracturefeaturesofthespecimens. Ductilefractureobservedinallsamples.However,adistinct differenceoffracturemorphologiescanbeobservedbetween theasreceivedmaterialandFSPedcompositeswithnumberof passes.TheFSPednanoparticlescompositewiththreepasses showsfinerdimples,whichareassociatedwithfiner reinforce-mentofnanoparticles inthematrix alloy.Thenanosized compositeswithonepassFSPspecimenimproves the ten-silepropertiesandelongation,inthreepassnanoparticleFSP specimenobservedimprovedtensilepropertiesandslightly decreaseinelongationwhencomparedwithonepassnano particleFSP. Theincreaseindislocationdensitycauses the reductionofelongation.ThemicroparticleFSPedcomposites showslowertensilestrengthcomparedtothenanoreinforced compositesandfracturemorphologiesshowthelargerdimple sizewithreducedductility.

3.5. Wearproperties

ThewearbehavioroftheasreceivedAl5083alloy,FSPed with-outparticleonepassandFSPedwithreinforcementparticle (microandnanosizedB4Cparticleonepassandthreepass)

surfacecompositelayer(SCL)wereevaluatedbyapinondisc tribometer.Fig.14(a)showsthevariationofweightlosswith slidingdistanceoftheSCLsamples.Theweightlossoftheas receivedmaterialishigherthantheSCLsamples.Thehard B4C nano reinforcement particles exhibited the least wear

amongstthetestedspecimens.

Fig.14(b)showsthewearrateresults.Thewearrateofthe asreceivedAl5083alloysampleishighertheSCLsamples.The wearrateoftheB4Cnanoparticlewiththreepasssamplehas

lesswearrateascomparedtotheonepassnanoparticleand microparticlespecimen.

ReasonsforbetterwearresistanceoftheSCLascompared withunprocessedmatrixalloy.

1. ThedispersionofhardB4Creinforcementparticlesinthe

SCLinuniformmanner,whichincreaseshardnessdueto decreaseingrainsizeintheAlmatrix.Theseresultsare supportedbyAnwarietal.[47].

2. ThefinegrainsizeofmatrixalloyduetoFSPwithnumber ofpasses.

SimilarresultswerereportedbyShafiei-Zarghanietal.[42]

forAl–Al2O3 andDolatkhahetal.[22]Al–SiCnanoparticles

withfourpasses.ThewearresistanceoftheSCLwassuperior

1 2 3 4 5 6 Fe Al 80

a

b

60 40 20 0 o Mg B keV 7 8 9 10 1 2 3 4 5 6 Fe Al 50 40 20 10 30 0 o Mg B keV 7 8 9 10

Fig.17–(a)EDAXofwornsurfaceofAl–B4Cnanoparticle

FSPspecimenwiththreepasses(b)EDAXofwornsurface

ofAl–B4CmicroparticleFSPspecimenwiththreepasses.

totheasreceivedAlsubstrate duetoincreaseinhardness andpresenceofhardceramicparticlesandmatrixrefinement.

Fig.14(c)showsthechangeinwearratevsmicrohardness. AccordingtotheArchard’sequation,thewearrateisinversely proportionaltothehardnessofthematerial.Owingtothehigh hardnessofnanoparticlesandtheirbondingnature,thenano particlesresistthepenetrationandcuttingintothesurfaceby thecountermaterial[48–50].

Figs. 15 and 16 show the SEM micrograph ofworn

sur-face of the samples. The deep grooves occur in the base metalduetointensivematerialremovalandplastic deforma-tion.Innanocompositewiththreepassspecimen’sshallow groovesare seen onthe surfaceincomparisonwithsingle passnanocompositelayer.Presenceofceramicparticleinthe FSPedcompositelayerpreventsthewearanddrasticmaterial removalofmaterial.Fig.17(a)and(b)showstheEDAXofworn surfaceofAl–B4CnanoparticlethreepassFSPedspecimenand

Al–B4CmicroparticlethreepassFSPedspecimen.

Fig. 18 shows the variations of friction coefficient with slidingdistanceofthebasemetalandFSPedsamples.From

Fig.18(f),it isclearthattheaveragecoefficientinthethree pass nanoparticlehasthe lowestvalueof0.4.Thefriction coefficientinnanocompositelayerislowduetodecreasein adhesiveandlowerabrasivewearbecauseofhigherhardness. FurthermorethepresenceofwornoutB4Cparticlesactingas

0 500 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

a

b

1000 1500 2000 2500 Base material

Without particle one pass

Sliding distance (m) F riction coefficient F riction coefficient 3000 0 500 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

c

1000 1500 2000 2500

Micro particle one pass Micro particle three pass

Sliding distance (m) F riction coefficient 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

d

F riction coefficient 3000 0 500 1000 1500 2000 2500 Sliding distance (m) 3000 0 500 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

e

1000 1500 2000 2500 Nano particle one pass

Nano particle three pass

Sliding distance (m) F riction coefficient 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

f

F riction coefficient 3000 0 500 1000 1500 2000 2500 Sliding distance (m) 3000 0 500 1000 1500 2000 2500 Sliding distance (m) 3000

Fig.18–Variationsoffrictioncoefficientwithslidingdistancein(a)basematerial,(b)FSPedwithoutparticleonepass,(c) FSPedwithB4Cmicroparticleonepass,(d)FSPedwithB4Cmicroparticlethreepass,(e)FSPedwithB4Cmicroparticleone

pass,(f)FSPedwithB4Cnanoparticlethreepass.

Table3–Weartestresults.

Specimen Basematerial Withoutparticle

onepass

MicrosizedB4C

particleonepass

MicrosizedB4C

particlethreePass

NanosizedB4C

particleonepass

NanosizedB4C

particlethreepass

Wearrate(mg/m) 0.0057 0.00497 0.0046 0.00416 0.00363 0.00327

Friction coefficient

lubricantisalsoevidentfromthelowvalueoffriction coeffi-cientofnanocompositelayerwiththreepasses.However,the maximum(averagevalue) frictioncoefficientvalueofis0.6 observedinbasematerial.Presenceofhardreinforcing mate-rialinFSPedwithB4Cparticlespreventsadhesivewearingand

materialremoval.Table3describesthewearrateofthemicro andnanoparticlespecimenswithoneandthreepasses.

4.

Conclusions

Al/B4C compositeswerefabricated successfullybyoneand

threepassFSP.EffectofthereinforcingparticletypeandFSP passesonthemicrostructure,microhardness,tensilestrength andwearpropertiesofthefabricatedsurfacecompositelayer wereinvestigated.

1. ThemicrostructureintheFSPedspecimenswithnanoB4C

particlesthreepassesexhibitsfinegrainsize,higher hard-ness(124.8Hv),ultimatestrength(360Mpa)andwearrate (0.00327mg/m)incomparisontothebasematerial hard-ness (82Hv), ultimate strength (310Mpa) and wear rate (0.0057mg/m).

2. ByincreasingtheFSPpasses,thedistributionofnano parti-clesintheAlmatrixbecomesuniformwhichhasresulted inincreasedhardness,incomparisonwithonepassFSP nanocomposite.

3. ThemicrohardnessoftheAl/B4Csurfacenanocomposites

ishigherincomparisonwithB4Cmicroparticles.The

pres-enceofnanosizeB4Cparticlescontributestoproduceultra

finegrainsize.

4. TheFSPed nanosizedtensilespecimenonthe stirzone exhibitedbettermechanicalpropertiesthantheasreceived Al5083alloy.

5. The wear propertiesof the Al5083 alloy were improved byadditionofB4CnanoparticlesincomparisonwithB4C

microparticle,andthewearresistanceofthenanoSCLwas higherthanthatoftheunreinforcedAl5083alloy.

Conflicts

of

interest

Theauthorsdeclarenoconflictsofinterest.

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