Wear 271 (2011) 27662774Contents lists available at ScienceDirectWearj our nal homepage: www. el sevi er . com/ l ocat e/ wearAbrasivewearbehaviourofSiCp/AlalloycompositeincomparisonwithausferriticductileironY.Sahina,,V.KiliclibaDepartment of Manufacturing Engineering, Faculty of Technology, Gazi University, Besevler-06500, Ankara, TurkeybDepartment of Metallurgy and Materials Engineering, Faculty of Technology, Gazi University, Besevler-06500, Ankara, TurkeyarticleinfoArticle history:Received 13 October 2010Received in revised form11 May 2011Accepted 18 May2011Available online 26 May 2011Keywords:SiC particleAl alloyMetal matrix compositeDuctile ironAbrasive wearWear surfaceabstractTheabrasivewearbehaviourofSiCp/Alcomposites(MMCs)preparedby liquidmetallurgymethodwasinvestigatedtondouteffectsofappliedloadandweightfractiononapin-on-discconguration.TheMMCpinscontaining20wt.%particleswithsizesof50mandits2014Al alloyweretestedunderdiffer-entconditionsagainstSiC abrasives.ThewearperformancesofMMCswerealsocomparedwiththoseofductileiron(DI),partiallyaustenitizedandaustemperedductileiron(PADI)andconventionallyausten-itized(fullaustenitized)andaustemperedductileiron(CADI)undersimilarconditions.Moreover,wearsurfacesoftestedsampleswereexaminedinascanningelectronmicroscope(SEM).Hardness,densityand porosityincreasedwithincreasingwt.%ofparticleforthecomposite,butforthePADIandCADIsample,hardnessincreasedwithincreasingmartensitevolumefractionandausferritevolumefraction.The experimentalresultsshowedthatwearrateofthecompositedecreasedslightlywithincreasingSiCpcontentsandincreasedwithincreasingload.ThewearresistanceofMMCswas foundtobebetterthenthoseofDI,PADIandCADImaterials,whentestedagainst70msizesofabrasives.Furthermore,SEMexaminationshowedthata fewwearcraters,combinedwithre-attachmentofdebrisparticles,was dom-inantforthecomposite,butthefragmenteddebrisparticles,whentestedatlowerloads,werefoundthemoredominantforMMCs.Adhesion,chippingandabrasionwereresponsiblemechanismsforthealloy,but abrasionwasthemosteffectivemechanismfortheCADIsamples. 2011 Published by Elsevier B.V.1. IntroductionAluminium alloys are widely used in many automobile,aerospace and mineral processing components due to their excel-lent combination of low density and high thermal conductivityand high strength-to-weight ratio [1].However, they suffer frompoor elevated temperature and tribological properties. To over-come this, hard reinforcement phases such as particulates, bres,and whiskers are introduced into Al-based matrix for their highspecic strength, stiffness, wear resistance, fatigue resistance andelevated temperature [2,3]. Among the reinforcements such asSiCw, TiC, B, C and Al2O3, SiCp is the widely used due to its lowcost,wide range of available grades, more stable and chemical compati-bility with Al matrix. It has been generally observed that increasingthe SiCp or Al2O3 particle content enhances the wear resistance ofthe base alloy [4].There are several manufacturing techniques for particle rein-forced MMCssuch as squeeze casting, compo-casting, powdermetallurgy and mechanical alloying. The distributing of reinforce-Corresponding author. Tel.: +90 312 202 8671; fax: +90 312 212 00 59.E-mail addresses: ysahin@gazi.edu.tr (Y. Sahin), vkilicli@gazi.edu.tr (V. Kilicli).ment particles homogeneously in the metal matrix is a difculttask. Moreover, despite undesirable chemical reaction, the castingmethod, i.e. melt stirring process provides some advantages suchas cost efciency, good inltration, quality of chopped performs,and offers a wide selection of materials and processing conditions[5]. Particulate MMCsare isotropic in their properties and are eas-ier to process via powder metallurgy or cast ranging route. Dueto low processing cost and ease of preparation, Al matrix com-posites with different ceramic reinforcing particles showed goodmechanical properties and wear behaviour, compared to corre-sponding monolithic alloys [2,6]. SiC/Al composites have recentlyreceived particular interests due to their high specic modulus,high strength and high thermal stability for structural materi-als. Therefore, the applications of these composites have beenincreasedintheaerospace, automobiles industrysuchas driveshaftcylinder heads, pistons, discs of car brakes and jet ghter aircraftlings, where the tribological properties of the materials are veryimportant [79].Apart from MMCs, austempered ductile iron (ADI), partiallyaustenitized and austempered ductile iron (PADI) or ductile iron(DI), have alsoattractedmuchattentionfor its excellent mechanicalproperties such as high strength, toughness and excellent fatiguestrength. However, the resulting properties are strongly dependent0043-1648/$ see front matter 2011 Published by Elsevier B.V.doi:10.1016/j.wear.2011.05.022Y. Sahin, V. Kilicli / Wear 271 (2011) 27662774 2767upon the time and temperature of the austempering treatment[10,11]. Thus, ADI has becomeincreasinglyimportant for themanu-facturing of components such as gears, crankshafts, camshafts androlls, and PADIs have been found to be validated for suspensionparts of the automotive owing to its higher ductility then the con-ventionallyheat-treatedADIs [12]. Abrasivewear occurs whenhardparticles or asperities penetrate a softer surface and displace mate-rial inthe formof elongatedchips andslivers. Wear resistance is notan intrinsic property of material, but depends upon the tribologicalsystem, such as properties of materials tested, microstructure andinterface, abrasive grit size, test condition, equipment and envi-ronment [13,14].Dry wear and abrasive wear behaviour of metalmatrix composites have been investigated by several investigators[1546].The following is merely a brief overview of the work reportedon the wear behaviour of composites in the literature. Mondal et al.[25] studied the two-body abrasive wear behaviour of a cast alu-minium alloy 10wt.% Al2O3particle composite. They concludedalong with reinforcement size and the load and the interactionfactors were quite signicant. The abrasive wear performance ofpressure die casting Al composite reinforced with 10wt.% SiCp(5080minsize) was superior to that producedwithgravity cast-ing [2].The wear rate was primarily controlled by hardness eventhough other mechanical properties inuence the wear behaviourof thematerials tosomeextent. Sawla andDas [26] studiedthetwo-body abrasive wear behaviour of LM13 alloy and LM1315wt.%SiC composite as a function of load. It was observed that the wearconstant decreased with load, but the value of wear constant washigher for the cast alloy thanthat of the heat-treatedalloy andcom-posite. Kassimet al. [27] studied the abrasion of Al/SiCp compositesfabricated by a powder metallurgy route involving a nal hotextrusion step, with Al 1100 matrix and -SiC reinforcement withmean size of 10, 27 and 43m.The abrasion resistance increasedwith an increase in the volume fraction and size of SiC particles.Wilson and Ball [28] studied the abrasion wear resistance of theAA6061/20vol.% SiCp composite in short sliding distance testing(about 20m).There was a clear transition in wear mechanismwiththe use of ner abrasive grit sizes. As abrasive particle size reduced,the wear resistance of composites improved due to plastic defor-mation and cutting of the matrix, without SiCp fracture. On thecontrary, in the case of large abrasive particles whose size waslarger then the interparticle spacing, fracture and removal of SiCptookplace. Kiourtsidis andSkolianos [29] studiedthe abrasionwearbehaviour of T6 AA2024/40m-SiCp composites reinforced up to24vol.%. The composites wear resistant improved with increasingSiCp content in both the peak-aged (PA) and over-aged (OA) con-dition. The effect of particles size in T6 AA6061 alloy reinforcedwith SiC and Al2O3 particles was investigated by Zhang et al. [30].The wear performance of ne particle reinforced composites wasassociated with matrix hardness while the wear rate of large parti-cle reinforced composites was related to both matrix hardness andfracture of the particles.Wang and Hutchings [31] studied the two-body abrasion wearin relation to an Al6061 alloy reinforced with the Al2O3bresagainst SiC paper. With the larger abrasive particles, the wear resis-tance decreasedwithaverage bres volume fractions (20vol.%) andthe worn surface revealed bres fracture and extensive deboningat the bres matrix interface. Sheu and Lin [32] studied the effectof particle size on the abrasive wear of the Al alloy composites con-taining1030%Al2O3bres, wornonSiCandint grains. Theresultsshowedthat abrasivewear of thecompositeincreasedwithincreas-ing the abrasive grain size and load. Candan et al. [33] studied theinuence of low contact stress, the deleterious wear mechanismwas the digging out of SiCp from the Al matrix by the ploughingaction of the abrasive grains. In the case of large abrasive grains,wear resistance of Al/13mcomposites was nowhigher then thatoflarge SiCp reinforced composites. Bindumadhavan et al. [34]examined the wear performance of DPS (dual particle size) 47 and120m SiCp composites against SPS (single particle size) 47mSiCp composites and the higher load bearing capacity of the largerSiCp resulted in the protection of the smaller ones giving to DPS abetter wear performance then that of SPS composites.Sahin [35] carried out the abrasive wear test on Al2011 alloywith 510wt.% SiCp content with 3264m particle size, usingfactorial designs of experiments. The wear rate increased withincreasing the abrasive size, load and sliding distance when SiCpaper was used. However, the wear rate increased with increasingthe abrasive size, load and, decreased with sliding distance whenAl2O3emery paper was selected. A similar study was carried outon the MMCsexperimentally [4,13,36]. The results showed that theintroduction of SiC particles in the matrix alloy exerted the great-est effect on the abrasive wear, followed by load. It is also reportedthat MMCswere tested under different conditions [37,38].Last tworesults indicated that the abrasive grain size wasthe major param-eter on the abrasive wear, followed by the wt.% reinforcement andreinforcement size, respectively [39,40]. However, Modi et al. [41]showed that that the effect of applied load on the wear rate of bothzinc alloy and the 10wt.% Al2O3 particle reinforced composite wasmore severe as compared to that of the abrasive size at differentloads. Tjong andLan[42] foundthat the additionof only 5vol.%TiB2particle to copper led to a dramatic improvement in its wear resis-tance. ColacoandVilar [43] developedamodel for theabrasivewearof metallic matrix reinforced materials. The model was based on ageneralization to multiphase materials of Rabinowicz equation, byconsidering separately the contributions of the reinforcement par-ticles and of the matrix to material loss. Deuis et al. [44] reportedthat the controlling factors in composites wear; are the abrasivegrit size, hardness of the wearing surface in relation to that of theabrasivematerials andreinforcements meanpathinMMCsinaddi-tion to the fracture toughness of ceramic reinforcements. The wearperformance of MMCand its coating were inuenced by the type,size and volume fraction of the reinforcement phase and the wearenvironment [45,46].From the literature review, it is seen that most of the studieshas focused on the experimental work for abrasive wear behaviourof composites [2,4,5,2546], and DIs [4753],but there are a fewworks related to comparison of abrasive wear of MMCs with someother materials like high cast iron and intermetallic compounds[29,45,53].The aimof the present study is, therefore, to investigatethe abrasive wear behaviour of SiCp reinforced Al alloy compositesin terms of abrasive particle size, weight fraction and applied loadin pin-on-disc type of wear machine. Moreover, a comparison ismade with DI, PADI and CADIs under the same testing conditions.Furthermore, wear surfaces of MMCsand of their matrix alloy inaddition to DI based materials are also examined in a SEM.2. Experimental details2.1. MaterialsFor the fabrication of 20wt.% SiCp-reinforced MMCs, 2014 Alalloy wasused as the matrix material while SiC particles with anaverage size of 50m were used as the reinforcement materials.The matrix alloy used in this study waswidely used 2014 alu-minium alloy containing 0.8% Si, 4.2% Cu, 0.7% Mn,0.6% Mg andbalance Al. The composites were fabricated by a molten metal ofAlCualloyusinganelectric inductionfurnacewhichis 2kWpowerunder protected argon gas. For manufacturing MMCs, melting pro-cess was carried out in a crucible made fromgraphite while mixingprocess was conducted with a graphite mixer. The graphite mixerwasinserted into in a crucible when the melt temperature reached2768 Y. Sahin, V. Kilicli / Wear 271 (2011) 27662774to 500C. The temperature control of electric furnace and moltenmetal is carried out by NR911 type thermostat provided by NELInc. The mixer was xed on the mandrel of the drilling machine,started to stir the molten metal at about 670rev/min speeds aftercompleting the matrix alloy. The SiC particles were inserted ontothe aluminiumfoil by forming a packet. After completing the par-ticle addition, the molten mixture was poured in the pre-heatedmould made fromcast iron frombottomof the furnace. Details ofthe production method are given elsewhere [4,11].The ductile iron (DI) was produced in a medium frequencyinduction furnace in a commercial foundry. Samples fromthe bot-tom section of Y block of as-cast structure were intercriticallyannealed at various temperatures of 795 and 815C for 20min.The specimens were coded according to starting microstructureand partially austenitizing temperature like A795, A815. It is alsocalled as a partially austenitized and austempered ductile iron(PADI). The conventionally austempered sample wasalso codedas a C900 or CADI. The cast samples were heat-treated at theconventional austenitizing temperature of 900C in austeniticsingle-phase region () for 60minand then rapidly transformingto austempering temperature at 365C and holding at this temper-ature for various times and then air cooling to room temperature.More detailedinformationonthe productionandmechanical prop-erties can be found in the previous work [10].2.2. Abrasion wear testA pin-on-disc type of apparatus was employed to evaluate thewear characteristics of MMCs. The emery paper wasxed to a12mmthick, and 160mm diameter steel wheel to serve as theabrasive medium. The composite bars were machined into smallcylindrical shapes for using electrical wire machining in a pin-on-disc wear testing. The wear pin specimens made from the MMCswere approximately 5mmin length, too short to t into a standardwear machine. To forma pin of the necessary length, the cylinderswere bonded adhesively to a 50mmlong steel extension pin of thesame diameter using an epoxy adhesive, with a brass sleeve ttedover the joint for extra strength. The pin was then mounted in asteel holder in the wear machine so that it was held rmly perpen-dicular to that of the at surface of the rotating counter disc whentested. The samples were loaded against the abrasive medium bya cantilever mechanism. Wear tests were performed at roomtem-perature. The specimens experienced to continuous motion whilethe abrasive changed its position by the time (1min) the specimencompleted its cycle.The disc surface is regularly and thoroughly cleaned by acetoneprior to andafter wear testing. The wear tests were carriedout bothin dry conditions at different loads and for a xed sliding distance.The track radius has been kept at 90mmin length. The width of thewear track was 6.5mm.The track radius was measured to be thedistance between the centre of the disc and the central point of thetrack. A systematic view of the testing machine is shown in Fig. 1.The specimensurfaces were groundwell prior toinitiatingthe weartests and subjected to fewruns against the counter surface at slowspeed and low load for establishing intimate contact between thetwo matting surfaces.The composites were tested against SiC abrasive papers. In eachof these tests, the surface of the specimen was adjusted to com-pletely contact with abrasive particles before the abrasion test. Thespecimen of 6.4mm in diameter with a surface area of 40.9mm2for the composites was abraded under different loads against 180grits of SiC abrasives. This grit corresponds to 70m.After thetest, the wear pin was cleaned in acetone prior to and after thewear tests, then dried after that weighed on a micro-balance with0.1mgsensitiveness.Fig. 1. Schematic viewof the pin-on-disc test procedure.In the tests, normal load on the pin was variable at a constantsliding speed of 0.8ms1and the sliding distance was 48m.Eachtest was performed with a new abrasive paper and wasrepeatedfor three times and the average wasused. All the tests were per-formed with a range of loads from 8N to 32N. Wear losses wereobtained by detecting the mass loss of the samples before and afterthe wear tests. The wear rates were calculated by converting themass loss measurements to volume loss by using the respectivedensities [4].Specimens for metallographic observation were pre-pared by grinding through 800 grit papers followed by polishingwith 6mdiamond pastes.3. Results and discussion3.1. MicrostructureFig. 2 shows the optical micrograph of the aluminiumcompos-ite reinforced with a 20wt.% of SiC particle and 50m in size. Noevidence of the presence of cavities at interface in the matrix wasfound. The distribution of SiC particles in these composites wasalso uniform. The SiC particles (black colour) were observed to beangular in shape. This gure indicates that apart fromthe large SiCFig. 2. Microstructure of 50m 20wt.% SiCp reinforced 2014 Al composite.Y. Sahin, V. Kilicli / Wear 271 (2011) 27662774 2769Table 1Some mechanical and physical properties of Al alloy and its composite.Types of materials and their designations Weight fraction (wt.%) Density (kg/m3) Porosity (%) Hardness (BHN)Al-2014 alloy 0 2770 1.07 7950m-SiCp+Al-2014 alloy 10 2800 1.234 10550m-SiCp+Al-2014 alloy 20 2830 1.40 124Fig. 3. Microstructureof C900conventional sampleaustenitizedat 900Cfor 90minand then, austempered at 365C for a time of 60min.particles, ne SiC particles are present due to fracturing of particlesduring mixing process. Some mechanical and physical propertiesobtained for the Al alloy and its composite are given in Table 1. Thehardness increased with increasing contents and sizes of ceramicparticles in the composites.The nominal composition of ductile iron is (wt.%): 3.42 C; 2.63Si; 0.318 Mn;0.031 Cr; 0.0423 Ni; 0.0471 Mgand the balance Fe.The microstructure of as-cast material had ferrite graphite struc-ture [10]. Fig. 3 shows the microstructure of C900 conventionalsample austenitized at 900C for 90minand then, austemperedat 365C for a time of 60minetched with 2% nital. M letter inthis micrograph indicates Martensite. The microstructure of con-ventional the C900 samples with it is nearly wholly ausferriticstructure throughout the specimen. This micrograph also revealedthat there were graphites in the shape of spheroidal (black) dis-tributed throughout the whole sample. The mechanical propertiesand some metallographic measurements obtained for each heattreatment conditions are shown in Table 2. The hardness increasedwith increasing AFVF or with increasing martensite volume frac-tion. The C900 sample with highest AFVF had the highest hardnessvalue among the austempered samples.3.2. Wear behaviourFig. 4shows thevariationof averagevolumetric wear rates of theAl alloy matrix and its 10wt.% and 20wt.% SiCp reinforced compos-ites with 50m particle sizes as a function of applied load. Thesematerials were tested against 70msize of abrasive. It wasnotedthat the wear rate of the composite was less then that of the alloyTable 2Some metallographic andmechanical properties of different DI basedmaterials [10].Sample codes Ausferrite volumefraction (%)Martensite volumefraction (%)Hardness (BHN)As cast (DI) 168A795 (PADI) 10.5 14.3 203A815 (PADI) 23.6 38.2 251C900 (CADI) 37.5 52.3 327Fig. 4. Averagevolumetric wear rate as a functionof appliedloadfor the alloymatrixand its SiCp reinforced composite, tested against 70msize of abrasive.irrespective of all applied loads. For the composite, the hard rein-forcing SiC particles could be resisted against the micro cuttingaction of abrasives, and the lowest wear rate wasobtained for the20wt.% SiCp reinforced composite then that of the 10wt.% SiCpreinforced composite, but no signicant differences were observedbetween them due to a similar responsible mechanism duringabrasive wear (Fig. 4 and Table 3). Furthermore, it was evidentfrom gure that in the case of both alloy and the composite wearrate increased with increasing loads against xed abrasive sizes.Another reason was that the reinforcement particle of the 50mused for making MMCswasrelatively small in compared to the70msize of SiC abrasive. However, increasing trends in the wearrates, especially for the higher wt.% SiC particles wasless (Table 3).For the purpose of comparison, wear rates of DI, PADI and CADIswere testedunder the same testing conditions, andthe average vol-umetric wear rate of these materials are determined graphically inFig. 5. This gure shows the variation of average volumetric wearrate as a function of applied load for DI, PADI and CADIs, testedagainst the 70m size of abrasive. It was observed that for allthe materials tested wear rate increased linearly as load increased.Again, the CADI sample exhibitedthe lowest wear rate thenthose ofDI and PADI samples (Table 4) since these samples had the highesthardness and lowest ductility then those of other tested samples(Table 2). Acomparisonof Figs. 4and5showedthat the lowest wearrate wasobtained for the MMCthen that of CADI sample. This wasprobably due to the use of the 70m size of abrasive because thepenetration ability of abrasives and depthness decreased consider-ably against MMCs. The formation of wear mechanismwasanotherreason for behind this event, as will be observed in the upcomingsectionof wear surface analysis. There were some differences inthewear rates between CADIs and MMCs, when tested at various loadsagainst the same size of abrasive. For example, the wear rates wereabout 0.212mm3/m and 0.314mm3/m,when tested at 32N load,for the 50m 20wt.% SiCp composite and CADIs, respectively.2770 Y. Sahin, V. Kilicli / Wear 271 (2011) 27662774Table 3Average wear rate of the alloy and its MMC,tested at 70mabrasive grits.Load (N) Average wear rate of MMCs, tested at 70mgrits (mm3/m)Types of tested materials2014 Al alloy 10wt.% 50m-SiCp-reinforced MMCs20wt.% 50m-SiCp-reinforced MMCs1st run 2nd run 3rd run 1st run 2nd run 3rd run 1st run 2nd run 3rd run8 0.431 0.45 0.474 0.132 0.156 0.113 0.092 0.103 0.089160.904 0.866 0.0922 0.1785 0.20 0.155 0.1485 0.141 0.156241.289 1.410 1.350 0.2014 0.212 0.009 0.182 0.164 0.202321.556 1.432 1.456 0.265 0.297 0.232 0.2125 0.236 0.179Fig. 5. Average volumetric wear rate as a function of applied load for DI, PADI andCADIs, tested against 70msize of abrasive.For the A815 sample, wear rate was found to be about0.53mm3/mmat the same load. In other words, the wear rate ofthe 20wt.% SiCp composite was 1.52 times less then that of theCADIs, tested at 16N load. It meant that the selection of the com-posites became a very favourable when such an abrasive wasused.In order to understand the behind wear behaviour of these testedmaterials, wear surfaces were examined by SEM in the followingsection.Standard deviation in general increased with increasing load.It was more obvious for the Al alloy, especially for 24N and 32Nload, respectively (see Fig. 4). It might be due to forming a highertemperature between the matrix and disc, and resulted in moredelamination, abrasive grooves and craters (see Figs. 6a and 7b).In the case of the composite, standard deviation wasslightly lowerbecause introduction of ceramic particles into the matrix increasedthe hardness of the matrix and changed the wear mechanism. So,hard abrasion ne particles covered the surface and caused the lessFig. 6. Wear surface of the unreinforced alloy pin specimen tested at: (a) 8N loadagainst 70msize of abrasive, showing continuous grooves and (b) higher magni-cation of Fig. 6a, indicating a deformed region and some re-attachment of particlesoverthe base alloy of the pin surface. The sliding direction top to down.damage by protecting the surface of specimen (see Figs. 8 and 9). Itwas foundthat the error calculatedby using the difference betweenthe experimental data of wear rates was about 10% even at thehigher load conditions for the matrix alloy. Thus, the standard devi-Table 4Average wear rate of DI, PADI and CADIs, tested at 70mabrasive grits.Load (N) Average of wear rate of DI, PADI and CADIs tested at 70mgrits (mm3/m)Types of tested materialsAs cast A-795 A-815 C-9001st run 2nd run 3rd run 1st run 2nd run 3rd run 1st run 2nd run 3rd run 1st run 2nd run 3rd run8 0.261 0.246 0.288 0.2429 0.254 0.228 0.1895 0.182 0.20 0.1187 0.123 0.115160.413 0.403 0.434 0.366 0.392 0.345 0.3379 0.352 0.313 0.225 0.234 0.21824 0.534 0.547 0.516 0.4979 0.524 0.483 0.477 0.507 0.45 0.269 0.252 0.278320.597 0.576 0.612 0.55 0.574 0.533 0.521 0.504 0.556 0.314 0.331 0.297Y. Sahin, V. Kilicli / Wear 271 (2011) 27662774 2771Fig. 7. Wear surface of the Al alloy pin specimen tested at: (a) 32N load against70m size of abrasive, showing a smooth surface and (b) higher magnication,indicating some craters and some sticking of particles over the pin surface. Thesliding direction fromdown to top.ation is within the condence limit. Engineering materials like DI,PADI and CADI also showed more stable behaviour in comparisonto the matrix alloy, as shown in Figs. 4 and 5. Furthermore, devi-ation in Fig. 5 increased with load, but decreased with increasingthe hardness of both types of tested samples.3.3. Surface observationsThe worn ends of some of the wear pins were cut off and exam-ined in the SEM in order to study the morphology of the wearsurfaces. Fig. 6 shows the wear surface of the unreinforced Al alloy,tested at a sliding distance of 48m under 8N load, imaged in SEmode. This low magnication micrograph revealed that continu-ous grooves had formed on the surface of the pin. It wasobservedthat some re-attachment of particles occurred on the pin surface. Amagnied view of Fig. 6a is shown in Fig. 6b, which clearly showsthe particles attached along with the damaged region. Addition-ally, edge chipping and oxidized sticking particles were evident inboth micrographs. Fig. 6 shows the wear surface of the Al alloy pinspecimen tested at 32N load against the 70msize of abrasive. Asimilar wear surface was observed for this case. However, it mightbe observed that the extent of damaged regions and continuousgrooves in this case (Fig. 7a) was less then that of the loading at 8N(Fig. 6). Moreover, more debris particles are attachedtothe wearingsurface. Higher magnicationof Fig. 7b indicates that small amountof craters and some sticking of particles over the pin surface wereobserved due to generation of heat during the abrasive process. Itis worth mentioning that the presence of size of micro-grooving orFig. 8. Wear surface of the 50m 20wt % SiCp composite pin specimen testedat:(a) 8N load against 70m size of abrasive, showing a smooth surface but cov-ered with fragmentations of the ne abrasive particles and (b) higher magnication,indicating a reattachment of debris particles and a fewcraters over the surface. Thesliding direction fromtop to down.depth of damage was found to be signicantly less in this case thenthe case of samples tested at relatively lower loads.Fig. 8shows thewornsurfaceof the20wt.%SiCpreinforcedcom-posite with 50m particle size, tested at a load of 8N against the70mabrasive grits. This lowmagnication micrograph exhibiteda smooth surface but it was covered with fragmented debris parti-cles on the pin surface due to fracturing of ceramic particles withinsmall sizes. This is better shown in the SE image of higher magni-cation in Fig. 8b. The size of debris particles attached to the surfaceis about 28m.A fewof craters are visible on the pin surface, andthese wear craters were usually in the region of particle clusters.This small number of craters might be a reasonof the decreasingthepenetrationability of SiCabrasives against the 20wt.%SiCparticles.It is also anindicationof enoughinterfaces bonding betweenSiCparticle and alloy matrix. Thus, the depth of cut was not so deep. Onthe other hand, a third body was presented at the interface surface(Fig. 8a and b). This might be the retained debris particles fromthe previous wear events or abrasion particles. This type of wearresulted in decrease in the wear rate as the abrasive particle sizeand shape changed.Fig. 9shows the wear surface of the composite pinwiththe sameparticle size, but tested at a load of 32N. Worn surface of the com-posite possessed a relatively smooth appearance. It also showedthat there was no extensive damaged region on the pin surface dueto more contents of reinforcement particles in the matrix despitehigher load. It is an indication of enough bonding between the par-ticleandmatrix. Ahigher magnicationof Fig. 9a is showninFig. 9b.Moreover, this micrograph shows a fewcraters and embedded par-2772 Y. Sahin, V. Kilicli / Wear 271 (2011) 27662774Fig. 9. Wear surface of the 50 m 20wt.% SiCp composite pin specimen testedat:(a) 32N load against 70msize of abrasive, showing a very smooth surface and(b)higher magnication, exhibiting a few craters combined with re-attachment ofdebris particles. The sliding direction fromtop to down.ticles over the wear surface because of fracturing and removal ofsome particles. Under the applied loading condition, a smooth sur-face was observed due to the reduction in frictional forces on thewear surface. No considerable amount of oxidized particles overthe pin surface was observed.Depth and width of the grooves not only depended on the sizeof SiC particles chosen in the composite, but also on the abrasivesizes used against the MMCs. The hard reinforced particles reducedthe extent of penetration of the abrasive particles on the speci-mensurface, thereby protecting the softer matrix surrounding thehard second phase. The materials hardness determined the depthof indentationof the abrasive particles, thus inuencingthe relativepenetration depth value [40,44]. The wear resistance of the com-posite improved because of not fracturing so much big particles, asevidencedinFigs. 810. MMCsindicatedalower wear ratethenthatof DIs based materials at the 70msize of abrasive particle, sincefracture and removal of SiC particles in the composites occurrednot easily since interparticle spacing was smaller. However, even asmaller size of abrasives had abilities in digging out of the surfaceof these engineering materials like DI, PADI and CADIs. It is in goodagreement with Wilson and Ball [28]. The previous studies carriedout by Sahin [3,4,13], Kiortsidis and Skolianos [29], Candan et al.[33], Bindumadhavan et al. [34] and Sahin and Ozdin [36] showedthat the large particles in the composites bore the most of the wearload. However, it was opposite the work carried out on aluminiumbased composite by Wilson and Ball [28], Zhang et al. [30], Wangand Hutchings [31] and Sheu and Lin [32].Fig. 10 shows the wear surface of the C900 sample, tested at thesame loads and particle sizes, as tested in the previous samples.Fig. 10. Wear surface of the C900 pin specimen tested at: (a) 8N load, showingne continuous abrasive grooves and (b) higher magnication of Fig. 10a, showingabrasive grooves and oxidized particles sticking to the surface. The sliding directiontopto down.Fig. 10a shows continuous grooves throughout the sample. Thesegrooves were caused by the ploughing action of hard asperities onthe emery paper. It is exhibited that the hard materials were tested.On the other hand, this sample contained about 90% martensitevolume fraction. Therefore, its hardness is about 327 BHN com-pared to the cast sample, which is about 168 BHN. A different formof wear surface wasobserved for the C900 sample, compared tothe MMCs. The wear debris formed at this load had a tendency tostick to the wearing surface. An increased view of this sample isshown in Fig. 10b. This micrograph indicated the abrasive groovesand oxidized particles sticking to the surface more clearly.Fig. 11ashows the wear surface of the C900 pin specimen testedat 32N load, showing a relatively smooth surface with ne abra-sive grooves. A higher magnication of Fig. 11bshows a smoothsurface, but combinedwithsome continuous abrasive grooves. Fur-thermore, it is seen that the wear surface of the pin in Fig. 11aissmoother thenthat of Fig. 10a,whichis causedbytheincreaseintheload. The graphite nodule wasalso covered with a deformed layerbecause of the increased load. This micrograph revealed that therewere graphites (black colour) distributed throughout the rubbingsurface and some oxidized debris particles were reattached to thepin surface due to generating of heat at the interface and repeatedprocesses. These debris particles were found to be small equiaxedparticles. The abrasive groove widthinthis specimenwas toosmall.On the contrary, wearing groove width of the pin specimen fromthe alloy wasabout 50mor even higher (Fig. 6).The previous work showed that applied load and hardness weremost important factors affecting the abrasion wear process [47]. ItY. Sahin, V. Kilicli / Wear 271 (2011) 27662774 2773Fig. 11. Wear surface of the C900 pin specimen tested at: (a) 32N load, showing arelatively smooth surface with ne abrasive grooves and (b) higher magnicationofFig. 11a showing a smooth surface but combined with some continuous abrasivegrooves. The sliding direction fromtop to down.is true for the DI, PADI and CADI samples. For the MMCs, however,the microstructure and formation of wear mechanisms became adominant factor for the wear behaviour. In the current study, theabrasive wear behaviour of SiCp reinforced Al alloy composites wasinvestigated in terms of weight fraction and applied load. A com-parison of abrasive wear of MMCswas made with different DIsunder the same testing conditions. The MMCsshowed a better per-formance due to the microstructure of the MMCsconsisting of hardceramic particles in a macro-scale then those of the microstructureof DI, PADI and CADIs comprising of ferrite graphite, ferrite, ausfer-rite or martensite inanatomic-scale. Alower wear was obtainedforMMCsdespite the fact that its hardnesss of MMCswasmuch lowerthen those of the PADI and CADI samples (Table 3). To summarize;microstructure and size of SiC particles in the matrix (50m)and size of abrasive particles (70m)in addition to formations ofwear mechanisms were found to be the dominant factors for bothabrasive wear behaviour of MMCs, and DI based materials for thisstudy.4. ConclusionsThe experimental results demonstrated that the addition of the20wt.% SiC particle to the Al alloy led to a dramatic improve-ment in wear resistance of the base alloy. The wear resistanceof MMCs was found to be better then those of DI, its alloy andheat-treated samples, tested at the 70m size of abrasive. Thewear resistance increased with increasing wt.% particles for MMCsand martensite volume fractions for PADI and CADIs, respectively.Furthermore, SEM examination indicated that a relatively smallamount of wear craters, combined with re-attachment of debrisparticles due to occurring the small amount of fractured particlesin MMCsbecause the 70msized abrasives were used against thecomposite reinforced with the 50m size. For lower loads, how-ever, fragmentation or pulverization sticking to the wear surface inaddition to the strong adhesion on the wear surface was effectivefor MMCs, which led to a greater number of sticking abrasive par-ticles. In general, smoothening mechanism was observed for bothtypes of materials under higher loads as well. Moreover; adhesion,chipping and abrasion were more obviously observed for the alloymatrix, but the abrasion became the most effective for the CADIsample.References[1] J.M. Torralba, C.E. Da Costa, F. Velasco, P/Maluminiumcomposites: anoverview,Mater. Process. Technol. 133 (2003) 203206.[2] Y. Sahin, S. Ozkan, Dry wear behaviour of SiCp/2014 Al alloy composite ,in: E.Ciulli, B. Piccigallo, R. Bassani, J. Vizintin, R. Crockett (Eds.), Proceedings of the2nd European Conference on Tribology, ECOTRIB 2009, Engineering Faculty,University of Pisa, Pisa, Italy, June 710, 2009, pp. 337342.[3]Y. Sahin, K. Ozdin, Amodel for the abrasive wear behaviour of aluminiumbasedcomposites ,Mater. Des. 29 (2008) 728733.[4] Y. Sahin, Kompozit Malzemelere Giris , Seckin Yayn &Da gtm, Ankara, Turkey,2006 (Turkish).[5] S. Das, D.P. Mondal, G. Dixit, Correlation of abrasive wear with microstruc-ture and mechanical properties of pressure die-cast aluminium hard-particlecomposite , Metall. Mater. Trans. 32A (2001) 633638.[6] K.H. Min, B.-H. Lee, S.-Y. Chang, Y.D. Kim, Mechanical properties of sintered7xxxseries Al/SiC composites ,Mater. Lett. 61 (2007) 25442546.[7] R.L. Deuis, C. Subramanian, J.M. Yellup, Abrasion wear of Al composites areview, Wear 201 (1996) 132144.[8] J.F. Kaczmar, K. Pietrzak, W.Wlosinski, The productionand applicationof metalmatrix composite materials , Mater. Process. Technol. 106 (2000) 5867.[9] R.K. Uyyuru, M.K. Surappa, S. Brusetheug, Tribological behaviour of AlSiSiCpcomposites/automobile brake pad systemunder dry sliding conditions , Tribol.Int. 40 (2007) 365373.[10] Y. Sahin, M. Erdo gan, V. Kilicli, Wear behaviour of asutempered ductile ironswith dual matrix structures , Mater. Sci. Eng. A 444 (12) (2007) 3138.[11] Y. Sahin, M.Erdo gan, M.Cerah, Effect of martensite volume fraction and tem-pering time on abrasive wear of ferrite ductile iron with dual matrix ,Wear 265(12) (2008) 196202.[12] Y. Sahin, V. Kilicli, M.Ozer, M.Erdo gan, Comparison of abrasive wear behaviourofductile iron with different dual matrix structures ,Wear 268 (12) (2010)153165.[13] Y. Sahin, Tribological behaviour of metal matrix andits composites , Mater. Des.28(2007) 13481352.[14] K.M. Shorowardi, T. Laoui, A.S.M.A. Haseeb, J.P. Celis, L. Froyen, Microstructureandinterface characteristics of B4C, SiC and Al2O3reinforced Al matrix com-posites: a comparative study , Mater. Process. Technol. 142 (2003) 738743.[15] K.H. Gahr, Wear by hard particles , Tribol. Int. 31 (10) (1998) 587596.[16] S.M. Zebarjad, S.A. Sajjadi, Microstructure evaluation of AlAl2O3compositesproduced by mechanical alloying method , Mater. Des. 27 (2006) 684688.[17] S. Zhiqiang, Z. Di, L. Guobin, Evaluation of dry sliding wear behaviors of SiCpreinforced aluminiummatrix composites , Mater. Des. 26 (2005) 454458.[18] J.A. Garcia-Hinojosa, C.R. Gonzalez, J.A.I. Juarez, M.K. Surapa, Effect of grainrenement treatment on the microstructure of cast Al7SiSiCp composites ,Mater. Sci. Eng. A 386 (2004) 4560.[19] A.M. Al-Qutub, I.M. Allam, T.W. Qureshi, Effect of sub-micron Al2O3concen-tration on dry wear properties of 6061 aluminium based composite , Mater.Process. Technol. 172 (2006) 327331.[20] M. Rahimian, N. Ehsani, N. Parvin, H.R. Rahavandi, The effect of sinteringtemperature and the amount of reinforcement on the properties of AlAl2O3composite , Mater. Des. 30 (2009) 33333337.[21] M. Rahimian, N. Parvin, N. Ehsani, Investigation of particle size and amount ofalumina on microstructure and mechanical properties of Al matrix compositemade by powder metallurgy , Mater. Sci. Eng. A 527 (2010) 10311038.[22] H. Wang, R. Zhang, X. Hu, C.-A. Wang, Y. Huang, Characterization of a powdermetallurgy of SiC/CuAl composite , Mater. Process. Technol. 197(2008) 4348.[23] A.K. Mondal, B.S.S.C. Rao, S. Kumar, Wear behaviour of AE42+20% safl Mg-MMC, Tribol. Int. 40 (2007) 290296.[24] A. Mazaheh, H. Abdizadeh, H.R. Baharvandi, Development of high-performanceA356/nano-Al2O3 composites , Mater. Sci. Eng. A 518 (2009) 6164.[25]D.P. Mondal, S. Das, A.K. Jha, A.H. Yegnesswaran, Abrasivewear of Al alloy-Al2O3particle reinforced composite: a study on the combined effect of load and sizeofabrasive , Wear 223 (1998) 131138.[26] S. Sawla, S. Das, Combined effect of reinforcement and heat treatment on thetwobody abrasive wear of aluminiumalloy andaluminiumparticle composites,Wear 257 (2004) 555561.2774 Y. Sahin, V. Kilicli / Wear 271 (2011) 27662774[27] S. KassimAl-Rubaie, N.H. Yoshimura, M.B.J. Daniel, Two-body abrasive wear ofAlSiC composites ,Wear 233235 (1999) 444454.[28] S. Wilson, A. Ball, Tribologyof compositematerials , in: P.K. Rohatgi, P.J. Blau, C.S.Yust (Eds.), Conference Proceedings Oak Ridge, ASM International, MaterialsPark, OH, May13, 1990, pp. 114.[29] G.E. Kiourtsidis, S.M. Skolianos, Wear behavior of articially agedAA2024/40m SiCp composites in comparison with conventionally wearresistant ferrous materials, Wear 253 (2002) 946956.[30] Z.F. Zhang, L.C. Zhang, Y.W. Mai, Particle effects on friction and wear of alu-miniummatrix composites, J. Mater. Sci. 30 (1995) 59996004.[31] A.G. Wang, L.M. Hutchings, Two body abrasion wear of Al6061 alloy reinforcedwith Al2O3 f, Mater. Sci. Technol. 5 (1989) 7176.[32] S.-Y. Sheu, S.-J. Lin, Particle size effect on the abrasion wearsof20vol.% SiCp/7075 Al composites, Scripta Mater. 35 (1996)12711276.[33] E. Candan, H. Ahlatci, H. Cimenoglu, Abrasive wear of AlSiC composites pro-duced by pressure inltration, Wear 247 (2001) 133138.[34] P.N. Bindumadhavan, H.K. Wah, O. Prabhakar, Dual particle size (DPS) com-posites: effect on wear and mechanical properties of particulate metal matrixcomposites, Wear 248 (2001) 112120.[35] Y. Sahin, Wear behaviour of aluminium alloy and its composites rein-forced by SiC particles using statistical analysis ,Mater. Des. 24 (2003)95103.[36]Y. Sahin, K. Ozdin, The effect of abrasive particle size on the wear behaviour ofmetal matrixcomposites , in: S. Ghost, J.M. Castro, J.K. Lee (Eds.), AIPConferenceProceedings 712, NUMIFORM 2004 Conference, 8th International ConferenceonNumerical Methods Applications, The Ohio State University, 650 AckermanRoad Columbus, OH 43202, USA, 2004.[37] Y. Sahin, The prediction of wear resistance model for the metal matrix com-posites , Wear 258 (2005) 17171722.[38] Y. Sahin, Optimization of testing parameters on the wear behaviour of metalmatrix composites based on the Taguchi method , Mater. Sci. Eng. A 408 (2005)18.[39] J. Esteban Fernandez, M.R. Fernandez, R.V. Diaz, R.T. Navarro, Abrasive wearanalysis using factorial experiment design , Wear 255 (2000) 3843.[40] B.K. Prasad, S. Das, A.K. Jha, O.P. Modi, R. Dasgupta, A.H. Yegneswaran, Factorscontrolling the abrasive wear response of a zinc-based alloys silicon carbideparticle composite , Composites 28A (1997) 301308.[41] O.P. Modi, R.P. Yadav, D.P. Mondal, R. Dasgupta, S. Das, A.H. Yegnesswaran,Abrasive wear of ZincAl alloy10% Al2O3 composite through factorial design,J. Mater. Sci. 36 (2001) 16011607.[42] S.C. Tjong, K.C. Lan, Abrasive wear behaviour of TiB2 particle-reinforced coppermatrix composites , Mater. Sci. Eng. A 282 (2000) 183186.[43] R. Colaco, R. Vilar, A model for the abrasive wear of metallic matrix particlereinforced materials , Wear 154 (2003) 625634.[44] R.L. Deuis, C. Subramanian, J.M. Yellup, Three-body abrasive wear of compositecoatings in dry and wet environments , Wear 214 (1998) 112130.[45] S. Osman Ylmaz, Comparison on abrasive wear of SiCrFe, CrFeC and Al2O3reinforced Al2024 MMCs,Tribol. Int. 40 (2007) 441452.[46] M.Kok, Abrasive wear of Al2O3 particle reinforced 2024 aluminiumalloy com-posite fabricated by vortex method , Composites 37A (2006) 457464.[47] E.D. Robinowicz, Friction and Wear of Materials , Wiley, NY, 1965, p. 18.[48] G. Cueva, A. Sinatora, W.L. Guesser, A.P. Tschiptsch, Wear resistance of cast ironusedin brake disc rotors ,Wear 255 (2003) 12561260.[49] M.Hatate, T. Shiota, N. Takahashi, K. Shimizu, Inuences of graphites shapesonwear characteristics of austempered cast iron , Wear 251 (2001) 885900.[50] B. Bosnjak, B. Verlinden, B. Radulovic, Dry sliding wear of lowalloyed austem-pered ductile iron , Mater. Sci. Technol. 19 (2003) 650656.[51] N. Rebasa, R. Dommarco, J. Sikora, Wear resistance of high nodule count ductileiron, Wear 253 (2002) 855861.[52] B.A. Ceccarelli, R.C. Dommarco, R.A. Martinez, M.R. Martinez Gamba, Abrasionand impact properties of partially chilled ductile iron , Wear 256 (2004) 4955.[53]Y. Sahin, O. Durak, Abrasive wear behaviour of ductile iron , Mater. Des. 28(2007) 18441850.