An Overview of Metal Matrix Composite

7/28/2019 An Overview of Metal Matrix Composite

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JournalofEngineeringResearchandStudies E-ISSN0976-7916

JERS/Vol.II/ IssueIV/October-December,2011/72-78

and is able to be used up to 1600C. The high

thermal conductivity coupled with low thermalexpansion and high strength gives this materialexceptional thermal shock resistant qualities.Silicon carbide ceramics with little or no grain

boundary impurities maintain their strength to very

high temperatures,approaching

1600C with no strength loss. Chemical

purity, resistance to chemical attack attemperature, and strength retention at hightemperatures has made this material very popularas wafer tray supports and paddles insemiconductor furnaces. The electrical conductionof the material has lead to its use in resistanceheatingelementsforelectricfurnaces,and as a keycomponent in thermistors i.e. temperature variableresistors. The alloy designation for Al is basedon four digits corresponding to the principalalloying elements. The most importantalloying elements in aluminum alloy systems are

copper (2xxx), manganese (3xxx), silicon(4xxx), magnesium (5xxx) and zinc

(7xxx) [5,6]. The SiC particles used in aluminummatrix composites are hardener than tungstencarbide [7] this is the reason why SiC isrecommended by many researchers. MMCs

generally, consist of continuous ordiscontinuous fibers, whiskers, or particulatesdispersed in a metallic alloy matrix. Thesereinforcementsprovide thecompositewithpropertiesnot achievable in monolithic alloys [8].The mostcommonly used route for fabrication of these

composites has been through infiltration ofmolten metal into preformed and porous ceramicbodies. For example, Al-alloys have beensuccessfully infiltrated with hydraulic or gaspressure into SiC,Al2O3 andAlNperforms[9]. It

is very interesting to emphasize the influence thatthe reinforcing particle volume fraction has toexert on themechanicalpropertiesofMMCs[10].


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2.MMCsystemsandissuesfortheirprocessingMetal Matrix Composites are self-possessed of ametallic matrix (Aluminum, magnesium,copper, iron,Silicon,cobalt andadispersedceramic(oxides, carbides) or metallic (lead, tungsten,molybdenum) phase. The various Matrix of metalare Aluminum Matrix Composites (AMC),Magnesium Matrix composite, Titanium Matrix

Composite, coppermatrix composites used in thefield of composites.Aluminum Matrix Composites(AMC), this is the widest group ofMetalMatrixComposites. Matrices of Aluminum Matrix

Composites are usually based onaluminum-silicon(Al-Si) alloys and on the alloys of 2xxx and6xxx series. Aluminum Matrix Composites(AMC) are reinforced by, Alumina (Al2O3)or

silicon carbide (SiC) particles (particulateComposites) in amounts 15-70 vol.%,Continuous fibers of alumina, silicon carbide,

Graphite (long- fiber reinforced composites),Discontinuous fibers of alumina (short-fiberreinforced composites). Silicon carbide compositesare attractive as structural materials in fusionenvironments because oftheir low activation, highoperating temperature and strength. The physicalproperties of composites are generally anisotropic.Silicon carbide particles, ranging in size from about12 to 38 microns, added to the standard aluminumalloys involumesof20 to40percent.20% or 30%are more commonly specified to achieve thefollowing advantages with lower density than

other alloy alternatives. Cast metal matrixcomposites has achieve much success and expertiseincastingof20-

40%siliconcarbideand thesealloys to theincreased

useofthesealloyshasnumerousapplications in thefield of CMMCs. High Speed automatedPrecision machinery, Silicon wafer processingequipment, seals, bearings, heat exchangers, hotflowgas liners, robotics, high quality reflective

mirrors, high performance bicyclejunctions andcomponents, Ball valve parts, fixed and movingturbine components, brake parts, optical and

laser equipment, semiconductormanufacturing equipment. CMMCs materialssatisfy these needs and requirements. The materialis readily melted and cast into complex

geometries utilizing our counter gravity

casting techniques. Cast Silicon carbide metalmatrix composites also can offer a lower costalternative to high beryllium content alloy

applications. Composite Parameters considered for

a given matrix/dispersed phasesystem:

Concentration

Size

Shape Distribution

Orientation

2.1ParticleReinforcedMMCsParticles used for reinforcing include ceramics

and glasses such as small mineral particles,metal particles suchas aluminum,

and amorphous materials, including

polymers and carbon black.


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Particlesused to increase themodulusofthematrixto decrease the permeability and ductility of thematrix.Particlesarealsoused toproduceinexpensivecomposites. Rein-forcers and matrices will becommon, inexpensive materials and are easily

processed.

Figure1.PhotoMicro-graphicimageofAl-SiCPMMCs made by dispersing a reinforcing material(SiC)intoametalmatrix(Al)asshowninfigure1.Thereinforcement surfacewillbecoated toprevent achemical reaction with the matrix. For example,

carbonfibersarecommonlyusedinaluminummatrixto synthesize composites showing low density andhigh strength. However, carbon reacts withaluminum to generate a brittle and water-solublecompoundon thesurfaceofthefiber. Toprevent thisreaction, the carbon fibers coated with nickel ortitaniumboride. Thematrixis themonolithicmaterialinto which the reinforcement embedded, and iscompletelycontinuous.

2.2Short Fiber-reinforcedMMCsProduction rates for short-fiber composites (both

alignedandrandomlyoriented)arerapidandintricateshapes formed which are not possible withcontinuous fiber reinforcement. The reinforcementmaterial embedded into the matrix. Thereinforcement does not always serve a purely

structural task(reinforcing thecompound),but isalsoused to change physical properties such as wearresistance, friction coefficient, or thermalconductivity. The reinforcement will be eithercontinuous or discontinuous as shown figure 2(a) and(b).

(a) (b)

Figure2.Shortfiberreinforcescomposite(a)Alignedand(b)Random.

Disc

ontinuousMM

Cswillb

e i

sotropi

c,

andwork

edwith standard metalworking techniques, such

as extrusion, forging or rolling. In addition,

they machined by using conventionaltechniques, but commonly would need the usepolycrystalline diamond tooling (PCD)

[11]. Discontinuous reinforcementuses whiskers", short fibers, orparticles. Themost common reinforcing materials in this category

are alumina and silicon carbide. Short- fiber

reinforced composites consist of a matrix


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reinforced by a dispersed phase in form ofdiscontinuous fibers (length < 100*diameter).

Applications involving totally multi directionalapplied stresses normally use discontinuousfibers, which are randomly oriented in the matrix

material. Consideration of orientation and fiber

length for particular composites depends on thelevel and nature of the applied stress as well asfabricationcost.

2.3Long FiberMMCsLong-fiberreinforcedcompositesconsist ofamatrixreinforced by a dispersed phase in form ofcontinuous fibers. Continuous reinforcement usesmonofilament arelargediameter(about 100-150m)

wiresorfibers suchascarbonfiberorsiliconcarbide.Monofilament are much less flexible thanmultifilaments, so they handled as single fiber,rather than bundles, and precautions are necessary

to avoid causing damage by imposition of sharpcurvature during handling. The fibers embeddedinto the matrix in a certain direction; the resultis an anisotropic structure in which alignment of

the material affects its strength. One of the firstMMCs used boron filament as reinforcement.

The term multifilament refers to relatively

small diameter (about 5-30 m diameter) fibers,which are flexible enough handled as tows or

bundles.

Figure3.Longfiberreinforcedfiber.Thesewoven,braided,filament wound. Thematerialconcerned includes carbon, SiC and various oxides.There has also been interest in carbon fiberreinforced zinc alloys, another system inwhich interfacial reaction are limited. While SiC

has

bee

nsu

ccessful in p

arti

cul

ateMM

Cs, multi-filament SiC fiber suitable for incorporation into

metallic matrices are not commercially available.Products on the market, under trade names suchas Nicalon, tend to have high levelsof free carbonand silica, leading to excessive reaction with mostmetallicmatricesduring processing.

2.4CermetsCermets are a composite material composedof ceramic (cer) and metallic (met) materials.Cermets are ideally, designed to have the idealproperties of both a ceramic, such as high

temperature resistance and hardness, and those of ametal, such as the ability to undergo plastic

deformation. The metal used as a binder for anoxide, boride, or carbide. Generally, the metallic

elements used are nickel, molybdenum, and cobalt.Depending on the physical structure of the

material, cermets can also be Metal matrixcomposites, but cermets are usually less than20%


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metalbyvolume. Typically, theceramicparticlesare1-10 m in diameter. One or more carbidecompounds bonded in a metallic matrix. Theterm cermets are not used for these materials, eventhough

it is technicallycorrect. Commoncementedcarbidesbased on tungsten carbide (WC), titanium carbide(TiC), and chromium carbide (Cr3C2)

.Tantalum carbide (TaC) and others lesscommon. Metallic binders: usually cobalt (Co) ornickel (Ni) Cermets used instead of tungstencarbide in saws and otherbrazed toolsdue to theirsuperior wear and corrosion properties. Titaniumnitride (TiN), titanium carbon nitride (TiCN),titanium carbide (TiC) and similar brazed liketungsten carbide if properly prepared however

theyneedspecialhandlingduringgrinding. TheAl-,Ti- and Mg-based matrices commonly used forMMCs are attractive in these terms, but are veryreactive in the liquid state, which often leads to

problemsduring this typeofprocessing.2.5StructuralMMCsThestructuralcomposites madeupofsandwichesor

laminated panels i.e. When a fiber reinforcedcomposite consists of several layers with differentfiber orientations, its multilayered (angle-ply)

compositeinlayeredform.Instructuralapplications,

the matrix is usually a lighter metal such asaluminum, magnesium, or titanium, and provides acompliant support for the reinforcement in hightemperature applications, cobalt and cobalt-nickelalloy. Themanufacturingprocessesusuallyhandlay-

up and atmospheric curing or vacuum curing areused.Metallicformshaveattractedinterest recentlypartly because processing advances have led tomaterialbecomingavailableat competitivecost and

partly because attractive property combinationsobtained, particularly in terms of specific stiffnessand specific energy absorption. Several approachesare available to metallic forms. Some of these,

particularly those generating closed cell structures,

involve processing the metal in the liquid or

semisolidstate.Aproblem thenarisesfrom the lowviscosity of liquid metals. Depending upon the

processing methodology employed but this iscommonly achieved by introducingdispersion ofceramic into the melt, either as oxide films or asceramicparticles,whichraiseitsviscosity. 3.ProcessingRoutesThe processesclassified according to whether the

matrixisin theliquid,solidorvaporphasewhileit iscombinedwith thereinforcement.

3.1.1StirCastingStir casting is a primary process ofcomposite production whereby the reinforcementingredient material incorporated into the moltenmetal by stirring. This involves stirring the meltwith ceramic particles and then allowing themixture to solidify. This can usually be preparedby fairly conventional processing equipment andcarried out on a continuous and semi continuousbasis by the use of stirring mechanismasshownfigure4.Aconcernis tomake


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sure that good particle wetting occurs. Difficultiescan occur from the increase in viscosity on

adding particles or, especially, fiber to a melt.However, the viscosity is sufficiently low toallow casting operations carried out.

Microstructure in- homogeneitiescan arise, notably particles

agglomeration and sedimentation in the melt.Redistribution as a result of particle pushing by

an advancing solidification front can also be a

problem. This reduced when solidification is rapid.

Stir casting often involves prolonged liquid-ceramic contact, which can cause extensiveinterfacial reaction. This hasstudied in detailed for

Al-SiC, whereformation ofAl4C3andsiliconwillbe

widespread.

Figure.4Schematicviewofstirringmechanismforthe Fabricationofcomposites

The both degrade the final property of the

composition and raises viscosity of theslurry, making subsequent casting difficult. The

rate of r

eaction r

edu

ced,

and

can b

ecom

e

zero, ifthe melt is Si-rich, either by prior alloying or as a

result of the reaction. The reactionKinetics and Silevels required to eliminate it are such that it hasaccomplished that casting of Al-SiCp involving

prolonged melt holding operations suited toconventional (high Si) casting alloys, but not tomost wrought alloys. Stir casting characterizedbyfollowingfeatures:

1. Content ofdispersedphase limited (usuallynot more than30%vol.).

2. Distribution of dispersed phase throughout

them

atrixi

snot p

erf

ectlyhomog

en

eou

s:(a) There are local clouds (clusters) of the

dispersedparticle(fibers);(b) Theres gravity segregation to thedispersed phase due to difference in thedensitiesofdispersedandmatrixphase.

3. The technologyisrelativelysimpleandlow-

cost.

3.1.2SqueezeinfiltrationInfiltration is a primary process of composite

productionwhereby themoltenmetalismade tofill,

spontaneously or using external mechanical work,pores within a preform of the reinforcementingredient. Pressure infiltration is an

infiltration process where hydrostatic pressureapplied onto the molten matrix surface to drivethe liquid into the preform. Pressure dieinfiltration is an infiltration process which uses a

pressuredie castingapparatus, where a preformis placed into a solid mould, and pressureinfiltration is effected witha moving solid


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pistoncausing turbulent flowofthemelt upstreamofthe perform. In connection with mechanical pressureinfiltration is a pressure infiltration process whichuses amoving solidpart to applypressureon themeltsurface driving the liquid into a preform. Liquidmetal is injected into the interstices of an assembly ofshort fibers, usually called a preform. Preform arecommonly fabricated by sedimentation of short fibers

fromliquidsuspension.Squeezecastinginfiltrationisa mechanical pressure infiltration process where apreform is placed into a solid mould, and pressureinfiltration affected with a moving solid piston

providing laminar flow of the molten matrix into themould. Variants include direct squeeze casting, inwhich the piston surface represents the final castingsurface; and indirect squeeze casting, in which the

piston acts on the ingate to the die.Various silica-andaluminum based mixtures have been popular as hightemperature binders. Squeeze Casting Infiltration is aforced infiltrationmethodof liquidphase fabrication of

Metal matrix Composites, using a movable mould part(ram) for applying pressure on the molten metal andforcing it topenetrateintoaperformeddispersed phase,placed into the lower fixed mould part, squeeze

Casting infiltration method is similar to the Squeeze

Casting technique used for metal alloys casting.

Squeezecastinginfiltrationhas thefollowing steps:

A perform of dispersed phase (particles,fibers)placedinto thelowerfixedmouldhalf.

1. A molten metal in a predetermined

amount pouredinto thelowermouldhalf

2. Theuppermovablemouldhalfmovesdown-wards and forces the liquid metal to infiltrate theperform

3. The Infiltratedmaterial solidifiesunder thepressure.

4. Thepart removedfrom themouldbymeansoftheejectorpin.

The method used for manufacturing simple smallparts (automotive engine pistons from aluminum

alloyreinforcedbyaluminashort fibers). Twomaintechniquesused to formand consolidate thepowder

are sintering and metal injection molding. Recentdevelopments have made it possible to use rapidmanufacturing techniques which use the metalpowder for the products. In practice, substantialpressures in the MPa range are likelyneeded.However, this technique thepowdermelted and notsintered,bettermechanicalstrengthaccomplished.

3.1.3SprayDepositionSpray casting/deposition is a primary process ofcomposite production whereby the metal sprayedontoasubstrate.Forcomposites, thereinforcement iseitheralreadyincorporated in thesprayedmelt (e.g.,by stir-casting), combined during spraying withthe metal, by injection of the reinforcementingredient material into the sprayed metal dropletstream,or is co-sprayed, i.e., sprayed at the sametime as the


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matrix onto the substrate. Spray depositiontechniques fall into distinct classes, depending

whether the droplet streamproduced froma moltenbath, or by continuous feeding of cold metal intoa zone of rapid heat injection. Adaptation toparticulate MMCproductionby injectionofceramicpowder into the spray has been extensivelyexplored, although with limited commercialsuccess. Droplet velocities typically average about

20-40 ms-1

. A thin layer ofliquid,orsemi-solid,isnormallypresent on the topoftheingot asit forms. MMCmaterialproducedin thisway often exhibits inhomogeneous distributionsofceramicparticles.Porosity in theas-sprayedstateis typically about 5-10%. Thermal spraying is

slower, but velocities arehigher. Porosity levels aretypically at least a few %. Unfortunately, it hasvery difficult to spray onto fiber arrays toproduce MMCs with acceptably low void

contents and there are also problem inmaintaininguniformfiberdistribution.

3.1.4ReactiveProcessingMany processes have developed in whichconstituents brought together under conditions

such that a chemical reaction occurs while themixtures consolidate. In some such processes,liquid metal introduced and progressively

oxidizes. The work originated in attempts to

ease melt infiltration, particularly withAl basedmelts, by reducing the pressure required for

infiltration. Ideally, wetting and / or chemical

reactionoccurringat theinfiltration front would besuch as to promote spontaneous infiltrationwithout the need for external application of

pressure. While it has proved difficult to promoterapid infiltration under these conditions, MMC

productsmadein thiswaywithgoodnearnet shapecharacteristics, particularly ceramic content ishigh while thermodynamic and Kinetic

details are complex and reaction takes placeto promote spontaneouspenetrationofanAl-based

melt into an array of ceramic particles or fibers.

TheAl, - SiC, - Ti, - and Mg based matrices

commonly used forMMCs are attractive in theseterms, but are very reactive in the liquid state,which often leads to problems during this typeof processing. As applications continue toexpand, the spectrum ofmaterials and processesemployed will remain relativelywide.

3.2Solidstateprocessing3.2.1PowderBlendingandconsolidationMMC diffusion bonding is a primary process forcomposite fabrication in the solid state, in whichstacksofmatrixmetalandreinforcement ingredients(usually parallel fiber monolayers and matrix

foils, see also fiber winding) encapsulated andbonded together after evacuation by mechanicalpressure at elevated temperature to enhancediffusion powder consolidation is a diffusion

bonding (primary) process in which matrix in

powder form blended orotherwise placed next tothe reinforcing ingredient material, andconsolidated with or without pressure and

elevated temperature. Blending of metallic


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powder with ceramic fibers or particulate is aversatile technique for MMC production.MMC produces by Powder blending arecommonly extruded. While MMC powder

extrusion is a consolidationofingredient materialswith application of pressure with an extrusion

press. Cold extrusion occurs below the re-crystallization temperature of the metal, hotextrusion at higher temperatures. This is usually

followed by cold compaction, canning,

evacuation, degassing and a high temperatureconsolidation stage such as Hot Isocratic Pressing(HIP)orextrusion.A featureofmuchpowder routematerial presence of fine oxide particles, usually

present in Al-MMCs in the form of plate

like particles a few tens of nm thick, constitutingabout

0.05-0.5vol%, depending on powder history andprocessingconditions. Thisfineoxide tends toact asa dispersion strengthening agent and often has a

stronginfluenceon thematrixproperties,particularlyat high temperature. Processes such as rolling

i.e. MMC powder rolling is ingredient materialswith application of pressure with a rolling mill.

And forging i.e. MMC powder forging isconsolidationofingredient materialswithapplicationofpressurewithaforgingpress.Involvehighdeviatorystrainsbeing

imposedquicklyandhencecancausedamagesuchascavitations, particle fracture and macroscopic

cracking, at particularly at low temperature. Very

high temperatures,andpossibilityofmatrixliquation,

on the other hand, can cause macroscopic

defects such as hot tearing or hot shortness. Incontrast to these forming processes, HotIsostatic Pressing (HIPing) generates no (volume-

averaged) deviatoric stresses and so is unlikely to

give rise to either micro structural or macroscopic

defects. MMC hot isostatic pressing (HIP) isdiffusion bonding of ingredient materials withapplication of hydrostatic pressure with a gas, at

temperatures high enough to effect concurrentsintering of the matrix, which for metal matrices

is generally above the matrix re-

crystallization temperature. However, it 's very

difficult to remove residual porosity in regionsofvery high ceramic content, such as withinparticle clusters, and absence of any microscopic

shear stress means that such clusters are notreadily dispersed during HIPing, leading to poor

inter-particlebonding.

3.2.2Diffusion BondingofFoils Foil-fiber-foilmethod (alsocalled foil-fibermethod) isaprimarycompositeproductionprocesswhereinlayers

of metal foil and ceramic monofilament fibersare alternatively stacked to produce precursor

materials for subsequent diffusion bonding,specifically hot pressing. While wire winding is

a method for production of precursor MFRM,

material produced by co-winding metal wires andceramic fibers forsubsequent diffusion

bonding, specifically hotpressing (MMC hot pressing is consolidation of

ingredient materials by diffusion bonding withapplicationofpressurewithapiston(ahot press)at

temperatures high enough to effect concurrent


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sinteringofthe matrix, which for metal matrices isgenerally above the matrix re-crystallization

temperature.),aliquidphase(at least temporarily)inthe compact. In connection with, powdercloth method are variant, foil-fiber-foilmethod forproduction of MFRM, in whichmatrix metal powders and a binder mixed andformed into a cloth or foil before stacking. One of

the main problems lies in avoiding excessivechemical reaction at the fiber/metal interface.

Additions ofAl, Mo or V slow the kinetics of

interfacial reaction, but also tend to make therollingofthinfoilsaredifficult.Ingeneral, the foil-fiber-foil route is cumbersome and obtaining highfiber volume fractions and homogeneous fiber

distribution is difficult unless specialtechniques used. Also, the process becomesdifficult when the aim is to produce parts of

complexshape.

3.3VaporStateProcessing

3.3.1PhysicalvaporDeposition(PVD)Coatingprocessesisaprimaryprocesseswhichcoatthematrixontoindividualreinforcement elementsof

the ingredient material (i.e. vapor deposition, or

electrolytic coating) creating composite elements,which generally require subsequent consolidation.

Vapor deposition (in the context ofcomposite production) is a primary processwherein the matrixdeposited from the

vapor phase onto individualreinforcement elements of the ingredient. Physical

vapor Deposition processes are relatively slow,butthe fastest is evaporation involving thermalvaporization to the target speciesinavacuum.It may

be noted that there is little or nomechanical disturbance of the interfacial

region; this of significance when thefibers have diffusion barrier layer, or tailoredsurface chemistry. Composite fabrication isusually completed by assembling the coated fiber

into a bundle and consolidating this in a hot

pressing or HIPing operation. A very uniform

distributionoffibersproducedin thisway,withfiber

contents of up to about 80%. The fiber volumefraction accurately controlled through thethickness of the deposited coatings and the fiber

distributionis always very homogeneous.While Electrolytic coating (in the context

of composite production) is a primary processwherein the matrix deposited from solutionusing

electrochemicalmeansontoindividual reinforcementelements of the ingredient material. In connectionwith matrix coated fiber method is a family of

primary coating process whereby

continuousormonofilament fiberscoatedwithmetal

matrix material by physical vapor deposition, orby sputtering techniquesorbychemicalmeansprior

to compositeconsolidation.

4.MECHANICALPROPERTIESComposite materials either isotropic or

anisotropic, whichdetermined by the Structure ofcomposites. Isotropic material is a material,properties of which do not depend on direction ofmeasuring.Anisotropic material is a material,

properties of which along a particular axis or

parallel to a particular plane are


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different from the properties measured along otherdirections.As shown in figure 5, Rule ofMixtures[ROM] is a method of approach to approximateestimation [12] of composite material properties,basedonanassumption that acompositepropertyisthe volume weighed average of the phases(matrix anddispersedphase)properties.

Figure5.RuleofMixtures4.1 ExperimentalThe paper highlighted on the Silicon Carbideproperties (in connection with mechanicalcharacteristics) of some particulate reinforcedcomposites,basedonacommercialaluminum alloy.

Several techniques followed by researchers for

the processing of particulatereinforced MMCs. Homogenous

dispersion of SiC particles in the Al matrix

shows an increase trend in the samplespreparedwithmanualstirringandwith2-stepmethod(bothmanualandautomatic)ofstircasting techniquerespectively. The composites meant for improving

the tribologicalpropertiesofthebase, and madeby

Vortex casting, in laboratory conditions, atthe Material Science and Engineering Faculty,in Technical University lasi [13]. Most of the

test for density, tensile strength, hardnessand elastic modulus and wear resistance of theprepared cast matrix and their compositioncarried out as perASTMstandards.

4.2HeatTreatmentsInorder to attenuate theabovecitednegative effectofthesoft particles,aheat treatment couldbeappliedon the composite specimens. Optimization of the

temperature and duration of the treatment playsan important role towards obtaining a goodcombination of the matrix pattern and certainproperties of the composite. In view of this, thecomposite samples submitted toasolutionhardening

treatments, First of all stirring system hasfollowed by rotating

mechanism.And themeltinghasdoneinanoilfiredfurnace.

Figure6. Effectofwt%SiCliquidustemperatureofcompositecasting.


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13. M. Mares, I. Carcea, R. Chelariu, C. Roman,Proc.

EUROMAT Conf.,Maastricht,1,423(1997).

Documents

An Overview of Metal Matrix Composite