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Procedia Materials Science5 ( 2014 )953 961 Available online at www.sciencedirect.com2211-8128 2014 Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).Selection and peer-review under responsibility of Organizing Committee of AMME 2014doi: 10.1016/j.mspro.2014.07.383 ScienceDirectInternational ConIerence on Advances in ManuIacturing and Materials Engineering, AMME2014Evaluation oI Sliding Wear Behavior oI Garnet Particle-ContainingLM13 Alloy CompositesAnju Sharmaa, Suresh Kumarb, Gurmel Singhaand O.P. Pandey`baDepartment oI Physics, Punjabi University, Patiala, -147004, INDIAbSchool oI Physics and Materials Science, Thapar University, Patiala, -147004, INDIAAbstractThepresent investigationaimstoevaluatethewearbehavioroIaluminum(LM13)alloycompositesreinIorcedwithgarnetparticles.TheliquidmetallurgytechniquewasusedtoIabricatethecomposites.ThereinIorcementcontentwas10wt.and15wt. garnet particles. A pin-on disc wear testing machine was used to evaluate the wear loss oI composites. The results revealthat the wear loss oI composites was less than that oI the aluminum (LM13) alloy, but increased with increase oI reinIorcement inloadandslidingdistance.ItwasIoundthatthewearresistanceincreaseswithincreaseingarnetcontentand decreaseswith thereinIorcedparticlesize.ThenatureoIwearhasbeenexplainedusingscanningelectronmicroscopy(SEM)analysisoIthewornsurIaces and debris. 2014 The Authors. Published by Elsevier Ltd.Selection and peer-review under responsibility oI Organizing Committee oI AMME 2014.Keyworas. metal matrix composites, wear, wear parameters, abrasion, delamination;`Corresponding Author:Dr. O.P. PandeyProIessorSchool oI physics and material science, Thapar University, Patiala-147004, IndiaTel: 91-175-2393116; Fax: 91-175-2393020, Email address: oppandeythapar.edu 2014 Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).Selection and peer-review under responsibility of Organizing Committee of AMME 2014954Anju Sharma et al. /Procedia Materials Science5 ( 2014 )953 961 1. IntroductionWiththeincreasingrequirementoIautomotiveindustry,highperIormanceandweightreductionhavebecomemainconcerntoimproveIuel eIIiciency and enhance thedrivingperIormance. Inorderto meettheserequirements,continuous eIIorts aremade to develop the compositematerials which are good candidates to achieve thisgoal. ThepresentstudyisconcernedwithmetalmatrixcompositeandmorespeciIicallyonthealuminummatrixcomposites(AMCs).AMCsreIertoclassoIlightweighthighperIormancealuminumbasematerialsystem|SudarshanandSurappain2008|.InAMCs,oneoItheconstituentsisaluminumalloy,whichIormspercolatingnetworkandistermed as matrix phase. The other constituent is embedded in this aluminum alloy matrix and serves as reinIorcement.ThisreinIorcementisusuallynon-metallicandcommonlyceramicssuchasoxides,carbides,nitridesandborides.GarnetisanattractivereinIorcementmaterialbecauseoIitsexcellentchemicalandthermalstability.Al -garnetcompositescanbeprocessedwithlow-coststircastingroutes.However,intheliterature,particlevolumeIractionvalues with diIIerent size are generally below10wt. in cast Al-garnet composites |Sharma et al. in 1998|. In recentyearsreinIorcementoIdiIIerenttypesoIparticleshavebeenstudiedbyHashimetal.|1999|,Dasetal.|2006|,Mirkhanlou et al.|2010| where the reinIorcement size was varied. Moreover, to the best oI our knowledge no work isreportedonslidingwearbehavioroIaluminumcompositesreinIorcedwithdiIIerentamountandsizeoIgarnetparticles.TheaiminvolvedindesigningmetalmatrixcompositematerialistocombinethedesirableattributesoImetalsandceramics.SincethemineralsarenaturallyoccurringsubstancesoitsapplicationoIdevelopedthecomposite will be economical. Moreover, garnet as reinIorcement has not been studied so Ior.2. Experimental Details2.1 Row Materials.In the present investigation LM13 aluminum alloy has been used as matrixmaterial. It was obtained in the IormoIingots.Thisalloyhasexcellentcastingpropertieswithreasonablestrength.ToIabricatecomposite,garnetwasused as a reinIorcingmaterial. The percentage oI garnetwas takenas10wt. and15wt.withdiIIerentparticlessize(50-75mand106-125m).GarnetisbasicallyasilicatematerialandisobtainedIromithasthehardnessvalues 1100 Hv. It is chemically inert at high temperature.2.2 Preparation of compositeThecompositewaspreparedbystircastingroute.RequiredquantityoILM13alloywastakeninagraphitecrucibleandmeltedinanelectricIurnace.ThetemperatureoImeltwasraisedto750C.ThismoltenmetalwasstirredusingagraphiteimpellerataspeedoI630rpm.AtthisspeedvortexiscreatedinthemeltandthereinIorcementmaterial is then introduced at the side oI the vortex with thehelp oI Iunnel kept on top oI the vortex.TheceramicparticlesusedasreinIorcementweretakenindeIinedproportionandmixedproperlybyspatula.Particlespriortomixingwerepreheatedat450 CtodriveoIIthemoisture.ThestirringiscontinuedIoraIewminutes beIore the slurry is cast. Stirring helps in transIerring particles into the liquid metal, and also maintaining theparticlesinastateoIsuspension.ThedevelopmentoIthevortexduringstirringisobservedtobehelpIulIortransIerring the particles into the matrix melt as the pressure diIIerence between the inner and the outer surIace oI themelt sucks theparticles into theliquid. Processing variables suchasholdingtemperature,stirringspeed,sizeoItheimpeller,andthepositionoItheimpellerinthemeltareamongtheimportantIactorstobeconsideredintheproduction oI cast metal matrix composites as these make an impact on mechanical properties. During production oIthe composite, the amount oI LM13 alloy, stirring duration and position oI stirrer in the crucible were kept constantto minimize the contribution oI variables related to stirring on distribution oI second phase particles.3. Material Characteri:ationThepreparedcompositeswerecutandpolishedmechanicallytoobservetheirstructureunderopticalmicroscope.The prepared composites were subjected to wear test under dry sliding condition at ambient temperatures (25-30C).955 Anju Sharma et al. /Procedia Materials Science5 ( 2014 )953 961 TestswereconductedonpinshapedspecimencutIromeachsetoIcompositeataconstantslidingvelocityoI1.6m/sec, using a pin on disc wear monitor. Pin shaped samples were made to slide against the hardened steel discs. Thewear testswere measured as a Iunction oI sliding distance at low load1kg and high load 5kg. SEM analysis oI weartracks and debris collected aIter wear test at low and high loads.4. Results and DiscussionThe microstructure, wear rate, worn surIace oI specimen aIter wear and wear debris are analyzed to understand themicrostructural evolution and wear mechanism involved in materialremoval oI the composites under investigation.4.1 Microstructural AnalysisHomogeneous distribution oI the garnet reinIorcement particles in the matrix is essential to Iorm a composite withuniIormmechanical properties. The optical micrograph oI composites reinIorced with 10 Iine and coarse particlesare shown in Fig.1 (a and b). The Fig.1 (a and b) shows the homogeneous distribution oI Iine and coarse particles inthe alloy matrix. The mechanical stirring not only distributed the particles homogeneously but also delays the particlesettling prior to solidiIication. Good bonding oI interIace between particle and alloy matrix is exhibited in the Fig.1.Rajanetal.in|2007|IindoutthatthesmoothinterIaceprovidesbettermechanicalandtribologicalpropertiesastransIeroIloadoccursthroughtheinterIace.TheopticalmicrographoIcontaining15wt.Iineandcoarsesandparticles is shown in Fig. 1 (b and d). It is observed that the garnet slightly segregate in the matrix due to their poorwettability with the matrix, which are disadvantageous to improve the mechanical properties oI the composites. TheincrementinamountoIgarnetreinIorcement10wt.to15wt.inmatrix,possibilityoIsegregationoIgarnetparticles increase with respect to decrement oI particles size. Garnet is distributed in the aluminum matrix, which caneIIectivelypreventthedislocationmovementintheLM13alloymatrix.WiththeincreaseoIthereinIorcementvolume Iraction, the interspaces between the reinIorcements decreaseinmatrix and thehindrancetothedislocationmovement enhances Iurther, which can lead to the Iurther increase in the hardness oI composites. Apart Irom this thematrixalsogetsmodiIiedIromdendritictocellulartypebecauseoIinterIerenceoIIeredbyIineparticlestothegrowingsolid-liquid interIaceasshown Iig.1 (a and c). Homogeneous distributions oI particles,which are arrangedin random Iashion due to limited amount oI coarse particle reinIorcement are seen (Fig. 1d). This can be explained bythe Iact that garnet particles have a lower thermal conductivity and heat diIIusivity than aluminum melt and thereIore,garnet particles are unable to cool down with the melt. As a result, the temperature oI the particles is higher than thatoItheliquidalloy.Thehotterparticlesmayheatuptheliquidintheirimmediatesurroundings,andthusdelaythesolidiIicationoIthesurroundingliquidalloy.Thegarnetparticlesgenerallyobservedareaccumulatedintheinterdendritic regions and geometrical trapping by dendrites is rarely observed. The observations by Zhang and Alpasin |1993|, Chaudhury et al. in |2005| and suggest that the garnet particles are always pushed by dendrite Ironts duringsolidiIication regardless oI the dendritic arm spacing.956Anju Sharma et al. /Procedia Materials Science5 ( 2014 )953 961 Fig. 1: The optical micrograph oI composites with reinIorced (a) 10 wt. Iine particles, (b) 10wt. coarse particles,(c) 15 wt. Iine particles, and (d) 15 wt. coarse particles.4.2 Wear characteristics4.2.1 Effect of sliaing aistance on wear rateAccording to Archard`s theory |1953|, the amount oI sliding wear is usually proportional to the applied load and theslidingdistanceandisinverselyproportionaltothehardnessoIthesurIacewornaway.ShearingoItheasperity957 Anju Sharma et al. /Procedia Materials Science5 ( 2014 )953 961 junctions can occur in one oI the two bodies depending on the relative magnitude oI interIacial adhesion strength andtheshearingstrengthoIsurroundinglocalregions.TheeIIectoIslidingspeedshowsareasonabledecreaseoIthewear loss. As shown in Fig. 2 ( a and b), the wear loss is more in the beginning. However, with the increase oI loadmore wear loss occurs. Further increase oI sliding distance results in the decrease oI wear loss due to the increase incontact area. Most metals oxidizes typically in air to Iorm oxide Iilm within a Iew minutes oI exposure oI the cleansurIace. This enables a constant wear rate oI material. At 1kg loads, the oxide Iilms separate the two metals and thecoeIIicient oI Iriction is low because the oxide has low shear strength and its low ductility limits the junction growth.At higher loads (5kg), the surIace Iilms deIorm and metallic contact occurs, leading to higher wear rate. The presenceoI oxide layer reduces the chance oI direct metallic contact and thereIore asperities interaction is reduced, which is aprerequisite Ior adhesive wear |Rajan et al. in 2007|. Higher load (5kg) results in surIace Irictional heating, which, inturn, results in the Iormation oI a thin molten layer at asperity contacts in the case oI low melting oI metals. The wearlossislessIorgarnetreinIorcedcompositesevenathighloads(5kg).TheoxidizeddebrisIormsthestablemechanicallymixedlayer(MML)onthesurIace.Thisenablematerialtowithstandthehighertemperaturescompared with other materials causing reduction in wear rate |24|.4.2.2 Effect of reinforcea ceramic particles si:e on wear rateThe variation oIwear ratewith sliding distance oI the composite has been investigated at Iive diIIerent loads whichare shown in Fig.2 and 3. It is observed that wear rate oI the composites increases with the increase in applied load.This representation concludes that Iine particle reinIorced composite exhibits better wear resistance in comparison tocoarseparticlesat1kgto5kgloads.TheIineparticleshavemoresurIaceareaincomparisontocoarseparticleinLM13alloymatrix.ThemoresurIacearea isrepresentingthemoreinterIaceareaoIthegarnetparticles,whichisresponsibleIorenhancedmechanicalpropertiesoIcomposites.ThenatureoIdistributionoIdiIIerentsizesecond-phase particles (garnet) may lead to development oI diIIerent sizes oI asperities because composite surIace roughnessdependsuponthereinIorcementparticlessize|Hashimetal.in1999|.FinereinIorcementcompositehaveIinesurIaceascomparedtocoarsereinIorcedcomposite.Astheloadisincreased,theseparationbetweensurIacesdecreases andmore oI the soIter asperitiesundergo changesinheight and shape by thepassage oI the highest hardasperities.ThecaseoIthestaticcontactbetweenanindividualhardasperityandasoItsurIaceisequivalenttoindenting a halI-space with a hard sphere. A more prominent asperity gives a greater compression and so develops ahighercontactpressure.ThewearresistanceoIthecompositesincreaseswithincreaseinreinIorcementoIgarnetsand in matrix. The wear behavior oI both composites increased with increase in applied load as shown in Iigure (2 &3). Forwear test at 1 to 5 kg loads, the wear rate oI the composite decreases constantly with the increase oI slidingdistance. Compared to low load, the higher applied load makes the varied region and increase in degree oI the wearsubsurIace. Moreover, some oI the cracked brittle blocks detached Irom the matrix re-enter into the aluminum matrixbytheappliedload,whichresultsinthereductionoIthecontactareaandthenumberoIjunctions,whichrequires958Anju Sharma et al. /Procedia Materials Science5 ( 2014 )953 961 less energy toshearduringthesliding.In addition,withtheincreaseoIthe appliedloads, theIrictionalheatonthewearsurIaceincreases.Hence,theoxidationlayerincreases,whichwillalsoreducethewearrate.Duringtherepeateddryslidingcontacts,theworkhardeningmayoccuronthewearsurIace,whichwillenhancethewearresistanceoIthecomposites|ZhangandAlpas,1993|.FromIigure(2&3),itcanbeseenthatthewearratesareslightlychangedbutbehaviorremainssamewithincreasingtheappliedload. Thismaybeattributedtothesteadyproperties oI the composites.500 1000 1500 2000 2500 3000024681012141618202224262830Wear rate x 10-3(mm3/m)SIiding distance (m) 1kg 2kg 3kg 4kg 5kg(a)500 1000 1500 2000 2500 3000024681012141618202224262830Wear rate x 10-3(mm3/m)SIiding distance (m) 1kg 2kg 3kg 4kg 5kg(b)Fig.2:Wear rate against the sliding distance oI the composites with 10wt. (a) Iine and (b) coarse garnet reinIorced.500 1000 1500 2000 2500 3000024681012141618Wear rate x 10-3(mm3/m)SIiding distance (m) 1kg 2kg 3kg 4kg 5kg(a)500 1000 1500 2000 2500 30000246810121416182022242628wear rate x 10-3(mm3/m)SIiding distance (m) 1kg 2kg 3kg 4kg 5kg(b)Fig. 3:Wear rate against the sliding distance oI the composites with 15wt. (a) Iine and (b) coarse garnet reinIorced.4.2.2 Morphological analysis of worn surface ana aebrisThe morphologies oI worn out surIace oI pins and debris oIIer clues to the wear mechanisms involved in sliding thesample against load. The SEM micrographs oI the Iine and coarse garnet sand reinIorced composites tested at loads959 Anju Sharma et al. /Procedia Materials Science5 ( 2014 )953 961 oI 1-5 kg at a speed oI 1.6 m/s are presented in Fig.4, which show the wear track morphology oI the specimen.Fig. 4: SEM micrograph oI wear tracks oI composite with 15wt. Iine size garnet reinIorced at (a) 1 kg, and (b) 5kgload.OneoIthecommonIeatureobservedinbothlowerandhigherload,istheIormationoIgroovesandridgeswhichappear parallel to the sliding direction in composites as can be seen in Iig.4 (a & b) respectively. On Iurther analyzingit has been Iound that wear grooves are Iine in worn pin surIace oI composite subjected to low load as compared tohigher load. The depth oI microploughing is increased on increasing load to 5 kg where contact asperities change theshape.Consequentlythe sizeanddepthoIthegroovesbecomegreateratthisstage.Weardebrisatlowandhigherload, i.e., 1 and 5 kg have been investigated and are presented in the study. Wear debris oI composite with 10 wt. Iine size garnet reinIorced at 1 kg and 5kg loads are shown in Fig.5 (a & b). The size oIwear debris is smaller oIcomposite with Iine particles at load as compared to high load. Wear debris oI composite with 15 wt. coarse sizegarnet reinIorced at 1 kg and 5kg loads is shown in Fig. 6 (a & b).960Anju Sharma et al. /Procedia Materials Science5 ( 2014 )953 961 Fig. 5: SEM micrograph oI wear debris oI composite with 10 wt. Iine size garnet reinIorced at (a)1kg, and (b) 5kgload.Fig. 6: SEM micrograph oI wear debris oI composite with 15 wt. Iine size garnet reinIorced at (a)1kg, and (b) 5kgload.TheweardebrisgeneratedisduetodelaminationoImatrixmaterial.SomeoIthedebriswhichishavingruggededges as shown is generated bymicrocutting action |Das et al.in 2006|. Figure 6 b shows that the debris is oI smallsize due to high load oI 5 kg although large metallic and microcutting chips are also seen.961 Anju Sharma et al. /Procedia Materials Science5 ( 2014 )953 961 ConclusionAluminiummatrix composites have been successIully Iabricated with Iairly uniIorm distribution oI garnet particles.DispersionoIgarnetparticlesinaluminiummatriximprovesthewearbehavioroIthecomposite. Finesizegarnetsandparticle reinIorced composite exhibitsbetterwearresistancethan coarseparticleatsameweightpercentageoIreinIorcement. The eIIect is the increase in interIacial area between aluminium matrix and garnet particles leading totheincreaseinstrengthappreciably.Theappliedloads,andslidingdistance,haveaneIIectonthetransitionwearcondition. Addition oI reinIorcement delays the transition point. MML was responsible Ior the decrease in the wear-rateAcknowledgementsTheauthorsarethankIultoArmamentResearchBoard(ARMREB),DeIenceResearchandDevelopmentOrganization (DRDO), India Ior providing Iinancial support under the letter no. ARMREB CDSW/2012/148 Ior thisstudy.ReferencesSudarshan,SurappaM.K.,2008,DryslidingwearoIIlyashparticlereinIorcedA356Alcomposites,Wear,349,360-265.Sharma, S. C., Girish, B. M., Kamath, R., Satish, B. M., 1998, Graphite Particles ReinIorced ZA-27 Alloy CompositeMaterials Ior Journal Bearing Applications, Wear, 162,168-219.HashimJ.,LooneyL.,HashmiM.S.J.,1999,Metalmatrixcomposites:productionbythestircastingmethod,J.Mater. Process. Tech., 92-9, 1-7.DasSanjeev,UdhayabanuV.,DasS.,DasK.,2006,SynthesisandcharacterizationoIZirconSand/Al-4.5wtCuComposite produced by Stir Casting Route,J. Mater. 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