Metall. Res. Technol. 114, 506 (2017)© EDP Sciences, 2017DOI: 10.1051/metal/2017033

Metallurgical Research

Technology&

Available online at:www.metallurgical-research.org

REGULAR ARTICLE

Conventional and microwave assisted sintering of copper-siliconcarbide metal matrix composites: a comparisonC. Ayyappadas1, A. Raja Annamalai2, Dinesh Kumar Agrawal3, and A. Muthuchamy1,*

1 Department of Manufacturing Engineering, School of Mechanical Engineering, VIT University Vellore, 632 014 Tamil Nadu,India

2 Centre for Innovative Manufacturing Research (CIMR), VIT University Vellore, 632 014 Tamil Nadu, India3 107 Materials Research Laboratory, Pennsylvania State University, University Park, 16802 Pennsylvania, USA

* Correspo

Received: 8 November 2016 / Accepted: 13 April 2017

Abstract. This study investigates the effect of heating mode on the sintering of Copper-SiC metal matrixcomposites containing up to 7.5wt.% SiC. The sinterability of the Cu-SiC system consolidated in a 2.45GHzmultimode microwave furnace has been critically compared with that processed in a radiatively heated(conventional) furnace. As compared to conventional sintering, microwave processing has resulted in a greaterdensification. It was observed that an increase in SiC content resulted in a higher hardness of the materials forboth the heating modes. For all compositions, the electrical conductivity and hardness of microwave-sinteredCu-SiC composites are higher than those of their conventionally sintered counterparts.

Keywords: composite / sintering / densification / hardness / electrical conductivity / wear

1 Introduction

Copper has been successfully employed to manufacturepowder metallurgy components since the advent ofpowder metallurgy technique. Copper has wide range ofapplications starting from microchips to the latest designelements in automotive industry [1–3]. It is excellent interms of its electrical conductivity and corrosionresistance. However, the use of monolithic pure copperlimited especially in heat sinking and electronic packag-ing applications [4], which require high thermal conduc-tivity combined with lower coefficient of thermalexpansion, which cannot be satisfied with the pure formof Cu. Some other applications demand for a higherhardness and strength with desirable conductivityvalues. Metal matrix composites (MMC) such as coppermatrix composites bridge the gap which results in a newclass of material with desirable properties. Coppermatrix composites have superior electrical, mechanicaland thermal properties as compared to that of purecopper by the inclusion of suitable reinforcement [5–7].They possess superior tensile strength, wear resistance,hardness and low coefficient of thermal expansion whichcould not be found in any single copper alloys or

nding author: a.muthuchamy@vit.ac.in

monolithic materials [4,6]. The mechanical strength ofcopper can be enhanced either by age hardening or byintroducing dispersoids into the copper matrix [1,4].These reinforcement particles which include some oxidesand carbides are thermally stable at higher temperature.Adding dispersoid particles in the copper matriximproves the mechanical properties of the composites.Cu-SiC metal matrix composites possess the properties ofboth copper and silicon carbide, with high thermalconductivity of copper and low coefficient of thermalexpansion of SiC [8,9]. This composite is primarily usedfor the heat sink or heat spreader applications because ofits high thermal conductivity and tailorable coefficient ofthermal expansion (CTE) over a desirable range. Copperbased MMC reinforced with SiC and carbon fiber arewidely used as packaging materials [10–12]. SiC rein-forced copper MMC’s are more effective as packagingmaterials since carbon fiber exhibits anisotropic behavior[10]. Innovators at NASA’s Glenn research recentlyreported successful development of SiC fibers and SiC/SiC ceramic matrix composites (CMC) which possessexcellent strength, toughness, lower thermal expansion,better life and creep rupture resistance at temperatureup to 1500 °C for gas turbine components [13]. This givesan insight to develop copper matrix composites with SiCaddition. Many researchers made successful attempts tofabricate and characterize copper based MMC’s. ChingYern Chee et al. fabricated Cu-SiC composites with

2 C. Ayyappadas et al.: Metall. Res. Technol. 114, 506 (2017)

coated and non-coated SiC particles. The interface pro-blems between SiC and copper matrix due to lack ofsufficient bonding between particles were particularlyaddressed [10]. G. Celebi Efe et al. investigated the effectof particle size on Cu-SiC composites and reported thatthe composites containing coarser SiC particles resultedin a higher densification and exhibited better properties[14]. A.S. Prosviryakov studied the effect of SiC contenton copper based MMC’s manufactured by mechanicalalloying. The study revealed that milling time and SiCcontent has a significant effect on the various propertiesof the composites. It was reported that over 25wt.%addition of SiC deteriorates these properties due tointense reduction in microstructural homogeneity [5].G. Celebi Efe et al. in another investigation studied theeffect of sintering temperature on Cu-SiC composites andreported 900 °C as the optimum sintering temperature.The mechanical, thermal and electrical properties werefound to be best at this temperature [6]. S.C. Tjong et al.employed hot isostatic pressing (HIP) to fabricate copperand copper composites reinforced with 5, 10, 15 and20wt.% SiC particles. Both dry sliding wear and abrasivewear measurements were made to study the effect of SiCcontent on properties of the composites. The authorsconcluded that SiC particles reduce the extent of weardeformation and dislocation movement which resultedin reduced wear rate and hardness [15]. In most of theaforementioned works, conventional sintering processwas employed to fabricate the composites. Some investi-gators derived a comparative study between convention-al and SPS process. Avijit Mondal et al. investigatedthe effect of heating mode and copper content on thedensification of W-Cu alloys fabricated by both conven-tional and microwave process. It was reported that allthe microwave-sintered composites exhibited improvedhardness and electrical conductivity as compared toconventionally sintered counterparts. Eighty-five percentreduction in processing time was achieved by microwaveheating [16]. Microwave assisted sintering was projectedas a promising processing technique for the sinteringof metal and alloy powders. Hence microwave assistedsintering was identified as an effective sintering processto fabricate these composites. Microwave assistedsintering is a faster processing technique for the consoli-dation of various materials. 2.45GHz multimode micro-wave systems for various materials processing includingsintering. Heat is generated in the material by micro-waves-matter interaction via dielectric heating (ceram-ics) and magnetic coupling (metals). Unlike theconventional process where thermal energy is transferredfrom the surface towards inside of the material, inmicrowave heating it is opposite from inside to outside.As a result of this, the temperature within the core maybe higher than the surface in microwave heating, whereasit is higher on the surface for conventional process[17,18]. Higher material diffusion in microwave processresults in finer microstructure and enhanced properties.Present investigation aims at finding the effect of SiCaddition on the mechanical, tribological and electricalproperties of copper based MMCs sintered by conven-tional and microwave process.

2 Experimental procedure

2.1 Materials

Gas atomised copper powder (distributed by SigmaAldrich, Bangalore, India) of 99.5% purity was used asthe matrix phase. Fine quality SiC powder of 99.9% purity(distributed by Sigma Aldrich, Bangalore, India) wasadded in Cu powder with the following ratios: 2.5, 5 and7.5wt.%. SEM micrographs of the as received copper andSiC powders are shown in Figure 1. The SEM micrographsreveal the spheroidal nature of the copper powder withan average particle size of 100mm. Irregular and angularshape of SiC particles with an average particle size of 20mmcan also be observed. The characteristics of the initialpowders are listed in Table 1.

2.2 Fabrication of Cu-SiC composites

Each composition containing 2.5, 5 and 7.5wt.% SiC andremaining copper powder were mixed thoroughly using apestle and mortar. Compaction of the powder mixture wasdone in a closed cylindrical die of 16mm diameter undera uniaxial pressure of 400MPa using a semi-automatichydraulic press (model: CTM-10, supplier: Bluestar, NewDelhi, India). Green compacts were having a heightranging from 4 to 6mm and diameter of 16mm. In orderto perform the dry wear test on the composites, another setof samples with square cross section were fabricated with arectangular section die of dimensions 31.7 x 4 x 4mm. Thesamples were compacted in the rectangular closed die witha uniaxial pressure of 400MPa. All the green compactswere sintered by conventional and microwave to study theeffect of sintering modes on the mechanical and micro-structural behavior of the composites. Both sinteringprocesses were performed at 900 °C in a reducing atmo-sphere (95%N2-5%H2) with a heating rate of 5 °C/min forconventional and 20 °C/min for microwave heating witha holding time of 1 hour for both. Conventional sinteringwas carried out in a tubular furnace (supplier: Indfurrsuperheat furnace, Chennai) with two intermediate holdsof 15minutes to drive out the volatiles. A low heating rateof 5 °C/min was set to avoid the thermal shock and damagein the furnace elements. Microwave sintering of the greencompacts was carried out using a multimode cavity2.45GHz, 6 kW commercial microwave furnace. Figure 2shows the schematic sketch of the microwave furnace usedfor the present study. A multi-layered insulation packagewas used to provide sufficient insulation to obtain high anduniform temperatures throughout the sample. The outerpackage was made up of thick ceramic fiber (alumina andsilicon carbide) sheets. A mullite tube was placed at thecenter of the package, and samples were placed inside thismullite tube. The entire package was placed on a turntableto ensure uniform exposure of the sample to the microwavefield. A reducing atmosphere was maintained during thesintering by first creating a vacuum of 8–10 torr inside thefurnace followed by back filling of a reducing atmosphere(95%N2-5%H2). Throughout the sintering, the gas flow wasmaintained at 2 L/min. For this experiment, a thin layer ofgraphite coating outside the mullite tube was used as a

Table 1. Powder characteristics of the as received copperand SiC powders.

Characteristics Copper Silicon Carbide

Apparent Density (g/cm3) 4.5 1.25Tapped Density (g/cm3) 5.3 0.28Flow rate in sec/ 50 g 30 12Particle size (mm)D10 13.82 8.52D50 30.53 21.36D90 62.02 42.36

Theoretical Density g/cm3 8.96 3.21Surface Area m2/g 0.246 0.152Shape Spherical AngularPurity > 99.5% 99.99%

a

b

Fig. 2. a: schematic diagram for configuration of multimodemicrowave furnace; b: schematic sketch of the 6 kW microwavefurnace used for the present investigation.

(a) (b)

Fig. 1. Scanning electron microimages of as received (a) copper powder (b) silicon carbide.

C. Ayyappadas et al.: Metall. Res. Technol. 114, 506 (2017) 3

susceptor. The susceptors usually couple very well with themicrowaves and are used for initially raising the tempera-ture of the compact. After sintering, the microwave powerwas switched off and samples were allowed to furnace cool.

2.3 Metallographic sample preparation

In order to obtain the optical micrographs of the sinteredsamples, metallographic preparation of the specimens wasperformed. The samples were polished in a semi-automaticpolishing machine (manufacturer: Bainpol; Model no:PMV 028; Supplier: Chennai metco) loaded with emerysheet grades of grit size 220, 600 and 1200. Later thesamples were polished in a disk-polishing machine using analumina medium. Fine alumina powder of particle size1mm was suspended in water to prepare the medium. Thepolishing process was carried out till a mirror finish wasvisible on the sample surface. ASTM E-407 standard forthe micro-etching of metals and alloys was followed to etchthe samples [19]. As per the standard, a solution containing5 g FeCl3, 10ml HCl, 50ml glycerol and 30ml water wasused as the etchant. The samples underwent a controlledetching process for a time period of 15–60 seconds. Sampleswere then dried instantly using a drier and viewed underan optical microscope.

2.4 Characterization

Sintered densities were determined using Archimedesprinciple. Microstructural analysis was done using opticalmicroscope (model: Axioscop A40, Zeiss, Germany) andScanning electron microscope (model: ZEISS EVO MA10,Zeiss, Germany). SEM-EDS analysis was performed onall the composites to determine the phase composition ofthe sintered samples. Micro-hardness test was performedusing a Vickers’ Micro-hardness testing machine (model:Matsuzawa MMT-X7, Japan, Supplier: Chennai Metco,

Fig. 3. Comparison between the temperature profile of conven-tional and microwave assisted sintering modes.

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Chennai) based on optical measurement systemwith a loadof 100 g and dwell period of 10 s according to ASTM E-384standard test procedure [20]. In order to confirm theprecision and repeatability of the hardness values, readingswere taken from five different locations on the compositesurface by carefully picking a location which included boththe matrix and reinforcement phase. The averages of thereadings were taken as the Vickers’micro-hardness value ofthe composite. In order to study the tribological behavior ofthe composites under applied loads, dry wear test wasperformed on the composites. The composite sample with asquare cross section of rectangular sample with thedimensions of 31.7 x 4 x 4mm. The test apparatus was apin-on-disc tribometer (model: TR-201LE, DUCOM, DiscMaterial: EN-31 Steel, Hardness: 60HRC) where thecomposite test specimen rubs against a rotating hardenedsteel disc which forms the pin and disc system according toASTM G-99 test procedure [21]. Disk rotation speed, weartrack diameter and sliding distance were made constant as500 rpm, 70mm and 1000m respectively throughout thetest. All the test samples underwent a varying load of 10, 20and 30N to study the effect of applied load on wear rate.Wear rate was calculated as the quotient of difference inmass of the composite before and after the test to the totalsliding distance.Wear rate indicates the removal of definitemass of the composite when subjected to unit slidingdistance during the pin-on-disk dry wear test. The LVDTconnected to the test apparatus measures the linear wearand coefficient of friction (COF) during the test. COFvalues were directly observed from the PC connected to thetest apparatus. Electrical conductivity of the compositeswas calculated in terms of electrical resistivity. Anelectrical resistivity measuring instrument (model: DDC-8, Chongqing, China) was employed to measure theresistivity values. The instrument works on the principleof four point Ohm analyses. A correction factor wasselected according to the size and shape of the specimen.The bulk resistivity of the specimen is governed by formula(1). The reciprocal of the average of these values were notedas the electrical conductivity of the composites.

Bulk resistivity ¼ 2pSðV =IÞ; ð1Þwhere S is the spacing of probe, V is the measured voltageand I is the current.

3 Results and discussion

3.1 Densification response

Heating profiles of both sintering processes are shown inFigure 3. Densification response of the composite materialto the sintering process for different SiC addition is shownin Table 2. Relative densities of the microwave-sinteredsamples were observed to be higher as compared to theconventional counterparts. This is due to the fact thatmicrowave-matter interactions cause higher rate ofmaterial diffusion resulting into higher sinterability ofthe composite material [22]. SiC particles prevent copper toplastically deform during the compaction process. There-

fore, with the addition of higher amounts of SiC powder willresult in poor densification of the sintered compacts[1,14,15]. Densification parameter is a measure by whichthe powder will densify upon the application of pressure,shown in equation (2). Densification parameters (p) forboth the processes are shown in Table 2. These valuesindicate the degree of densification attained during thesintering process. It can be inferred that the samplessubjected to microwave assisted sintering has undergonehigher densification.

Densification parameter

¼ Green density�Apparent density

Theoritical density�Apparent density:

ð2Þ

3.2 Microstructure and SEM-EDS analysis

Optical micrographs of the composites are shown inFigure 4. The bright colored areas indicate the coppermatrix whereas the dark spots indicate the uniformlydistributed SiC particles in the matrix. As the weightpercentage of SiC increases it was observed that the SiCparticles get embedded into the copper particles due tothe ductile nature of copper. Large grains of copper areclearly observed in the micrograph in all samples sincecopper particles have an average size of 400mm as shown.Microwave-sintered Cu-SiC composites were found to bemore homogeneous than the conventionally sinteredsamples. Some hard alumina particles of the order of1mm were also observed in the optical micrographs, theymight have got embedded into the soft copper matrixduring themetallographic preparations of the samples. Thedistinction between copper particles and SiC particles canbe made based on their respective sizes and contrasts asseen in Figure 5f. From the SEM micrographs (Fig. 5) theuniform distribution of SiC reinforcement (dark portion) in

Table 2. Effect of SiC addition and sintering mode (conventional versus microwave) on the densification response of theCu-SiC composites.

Composition Green density Sintered density Densification parameter

Sample 1 Sample 2 CON MWS CON MWS

Pure copper 7.88 (88%) 7.88 (88%) 8.06 (90%) 8.42 (94%) 0.17 0.5Cu-2.5 SiC 7.32 (83%) 7.23 (82%) 7.58 (86%) 7.93 (90%) 0.17 0.44Cu-5 SiC 6.68 (77%) 6.76 (78%) 6.93 (80%) 7.37 (85%) 0.13 0.32Cu-7.5 SiC 6.40 (75%) 6.40 (75%) 6.48 (76%) 6.82 (80%) 0.04 0.20

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the copper matrix (white portions) can be noticed.Substantial amount of porosity as expected can be seenin all the composites. It was also observed that the SiCparticles were located at inter-particular positions in thecopper particle network as shown in Figure 5e. Apart fromthe Cu-SiC interface, no other phases were seen in themicrographs of composites. The distribution of SiC inthe copper matrix was observed to be homogeneous for therange of addition used in the study. SEM-EDS analysisperformed on Cu-7.5 SiC is illustrated in Figure 6. Presenceof Si and C in the composite can be in turn predicted asSiC added to the copper matrix. Oxygen detected in theanalysis might come from the etching solution or aluminamedia used for the metallographic preparation of thesample.

3.3 Hardness, wear and electrical conductivitymeasurement

It is observed that the hardness increases with the additionof SiC for the range used in the study as shown in Tables 3and 4. Highest Vickers micro-hardness value of 82HV100was found for Cu-7.5 Sic sintered by microwave heating.Same trend was observed with higher load under aRockwell hardness tester. Microwave assisted sinteredCu-7.5 SiC composite exhibited a hardness of 64HRBwhilethe conventional counterpart showed only 54HRB. Purecopper exhibited a hardness of 36HV100 and 44HV100 forconventional and microwave process respectively. Rock-well hardness of the composites measured in B scale isshown in Table 4. SiC particles are excellent barriers to thedislocation movement in the copper matrix. An increase inthe SiC content strongly hinders the plastic flow, resultingin an increase of the hardness of Cu–SiC composites asshown in Table 3 [1,4,14]. The hardness values of thesecomposites were observed to be high despite the lowrelative density values. Similar trend was reported by otherresearchers [1,5,6,9,10,14]. This trend is attributed to thereinforced hard SiC particles which arrest the plastic flowin the matrix. All the microwave assisted sinteredcomposites exhibited higher hardness than conventionalsintered samples. Wear behavior of materials couldn’t beexactly correlated with the hardness values due todifferent varying parameters like materials properties,lubricating condition, sliding properties etc. that governwear behavior [2,23]. Pure copper exhibited high wear lossdue to low hardness and severe wear test conditions as

illustrated in Table 5 and Figure 7. Presence of macrogrooves and pits were observed in the worn out surfaces ofcopper samples as illustrated in SEM micrographs shownin Figure 6a,b. With an increase in the load, the wear lossis observed to increase as expected. With the increasingamount of SiC from 2.5 to 7.5% the wear resistance alsoincreases. As expected Cu-7.5 SiC composite showed highwear resistance due to improved hardness and a reductionof 1/16 times wear loss was observed under an appliedload of 30N. With the increase in load, SiC particle pull-out was observed as shown in Figure 6d. Reinforcementparticles got pulled out from the matrix resulting inexcessive wear and deterioration of the surface. S.C. Tjonget al. reported that volume loss due to wear is directlyproportional to sliding distance and load and inverselyproportional to hardness of the material, which isoriginally stated as Archard’s hypothesis of wear[13,24]. The SiC reinforcing particles with high hardnesscan offer protection to the Cu matrix during sliding. Cu-SiC composite also exhibited a high coefficient of frictionfor the entire range of loads. Highest COF was observedfor Cu-7.5 SiC with a value of 0.66 for 30N load as shownin Table 6. Delamination surface cracks were observedin the SEM images of worn out pure copper sample.High wear loss in pure copper was assisted by excessivedelamination of the surface layers. The extent of plasticdeformation was considerably reduced with the inclusionof hard SiC particles as it imparts sufficient hardness tothe material [1,4,14]. The incorporation of SiC particles incopper matrix is very effective in reducing the extent ofstrain localization in the subsurface region [4,14]. Theelectrical conductivity of pure copper was estimated as89% IACS and 92% IACS for conventional and micro-waved sintered samples, respectively (Tab. 7). Theelectrical conductivity of the Cu-SiC composite was foundto reduce drastically with the addition of SiC into thecopper matrix. The conductivity value of Cu-7.5 SiC wasobserved to be almost half that of annealed copper(100% IACS) for conventional as well as microwave-sintered samples. This was due to the presence of SiCceramic particles with low conductivity values and due tothe presence of porosity in the samples [1,3,14]. It ispossible to claim that the lower electrical conductivity ofcomposites containing higher amount of SiC may be dueto the presence of porosity and a small amount of oxidelayer formed during sintering at elevated temperaturewhich can be supported by EDS results.

Conventional Microwave

(c) Cu-2.5SiC (d) Cu-2.5SiC

(e) Cu-5SiC (f) Cu-5SiC

(a) Pure copper (b) Pure copper

Copper grains

SiC

Copper grains

SiC

(g) Cu-7.5SiC (h) Cu-7.5SiC

SiC

Fig. 4. Optical micrographs of Cu-SiC composites sintered by conventional (left) and microwave (right) sintering modes.

6 C. Ayyappadas et al.: Metall. Res. Technol. 114, 506 (2017)

Conventional Microwave

(c) Cu-2.5SiC (d) Cu-2.5SiC

(e) Cu-5SiC (f) Cu-5SiC

(a) Pure Copper (b) Pure Copper

Copper grains

porosity SiC

SiC

SiC

(h) Cu-7.5SiC

porosity

(g) Cu-7.5SiC

Fig. 5. SEM micrographs of Cu-SiC composites sintered by conventional (left) and microwave assisted (right) sintering modes:secondary electrons imaging mode.

C. Ayyappadas et al.: Metall. Res. Technol. 114, 506 (2017) 7

4 Conclusions

Microwave assisted sintering technique is successfullyemployed to fabricate copper-SiC composites. A compari-son of the effect of conventional and microwave heatingmode has been made on physical, mechanical and electrical

properties of the composites. Composites sintered bymicrowave process exhibited better densification responsedue to the fact that microwave-matter interaction providesbetter sinterability of a composite material. Faster pro-cessing in the microwave field resulted in the reductionof processing time by 60% as compared to conventional

Conventional Microwave

Composition Element Weight%

Atomic%

Cu-7.5SiCC K 5.20 17.99 Si K 2.05 2.51 Cu L 92.76 79.49

Composition Element Weight%

Atomic%

Cu-7.5SiC C K 6.62 25.48 Si K 0.03 0.05 Cu L 90.52 68.76

(a) Cu-7.5SiC (b) Cu-7.5SiC

Fig. 6. EDS analysis of Cu-7.5 SiC composite sintered by conventional (left) and microwave assisted (right) sintering modes.

Table 3. Variation of Vicker’s micro-hardness of thecomposites sintered by conventional and microwaveprocess.

Composition Hardness

Sintering mode !Conventional

Microwave

Pure copper 36±2 HV100 44±2.6 HV100

Cu-2.5 SiC 49±2.5 HV100 56±2.2 HV100

Cu-5 SiC 58±2.4 HV100 68±2.6 HV100

Cu-7.5 SiC 73±2.8 HV100 82±3.2 HV100

Table 4. Variation of Rockwell hardness of the compo-sites sintered by conventional and microwave process.

Composition Hardness HRB

Conventional Microwave

Pure copper 18±1 22±1Cu-2.5 SiC 24±3 28±2Cu-5 SiC 36±1 42±1Cu-7.5 SiC 54±1 64±1

Table 5. Variation of wear rate with respect to SiC content and sintering modes.

Composition Sintering mode ! Conventional Microwave 900 °C

Wear rate, g/m

10N 20N 30N

CONV MWS CONV MWS CONV MWS

Pure copper 3.10 2.40 5.60 4.80 9.36 7.86Cu-2.5 SiC 1.32 1.06 2.44 2.12 3.70 3.04Cu-5 SiC 0.66 0.50 1.25 0.86 1.98 1.30Cu-7.5 SiC 0.18 0.07 0.35 0.21 0.61 0.48

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process. Optical and SEM images revealed the homoge-neous distribution of SiC within the copper matrix. SEM-EDS analysis showed no formation of intermetalliccompounds in the composites. Vickers micro-hardness testshowed an increase in SiC content leads to correspondingincrease in the hardness due to the hard SiC particles whichprevent the plastic flow of Cu matrix. Microwave-sintered

composites exhibited better hardness and wear properties.A linear relationship between wear rate and applied loadwas observed. Electrical conductivity of pure copper ismeasured to be 88 and 94% IACS for conventional andmicrowave processes, respectively. Conductivity valuesfound to decline drastically with the addition of ceramicSiC particles. It can be concluded that microwave assisted

Conventional Microwave

(c) Cu-2.5SiC

(e) Cu-5SiC (f) Cu-5SiC

(d) Cu-2.5SiC

(a) Pure copper (b) Pure copper

Pit/gouge

Sliding direction

Micro groove

Sliding directionMacro groove

Particle pullout

(g) Cu-7.5SiC (h) Cu-7.5SiC

Micro groove Sliding direction

Fig. 7. SEM microimages of the worn out surface after dry wear test.

C. Ayyappadas et al.: Metall. Res. Technol. 114, 506 (2017) 9

Table 6. Variation of coefficient of friction (COF) with SiC content and applied loads.

Composition Coefficient of Friction (COF)

10 N 20 N 30 N

CONV MWS CONV MWS CONV MWS

Pure copper 0.48 0.56 0.54 0.52 0.58 0.54Cu-2.5 SiC 0.54 0.52 0.56 0.58 0.54 0.56Cu-5 SiC 0.59 0.60 0.62 0.60 0.64 0.62Cu-7.5 SiC 0.64 0.60 0.62 0.58 0.64 0.66

Table 7. Variation of electrical conductivity of the Cu-SiC composites sintered by conventional and microwaveassisted sintering process.

Composition Electrical conductivity, % IACS

Sintering mode!Conventional Microwave

Pure copper 88% IACS 94% IACSCu-2.5 SiC 72% IACS 80% IACSCu-5 SiC 58% IACS 65% IACSCu-7.5 Sic 47% IACS 54% IACS

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sintering technique is effective in imparting bettermechanical, electrical and tribological properties tocopper-SiC composites as compared to conventionalsintering process.

The authors gratefully acknowledge VIT University, Vellorefor the support through Seed Grant for Research. Also, theauthors C. Ayyappadas, A. Muthuchamy & A. Raja Annamalaiacknowledge the DST-FIST facilities at Department ofManufacturing Engineering, VIT University, Vellore.

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Cite this article as: C. Ayyappadas, A. Raja Annamalai, Dinesh K. Agrawal, A. Muthuchamy, Conventional and microwaveassisted sintering of copper-silicon carbide metal matrix composites: a comparison, Metall. Res. Technol. 114, 506 (2017)