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CHAPTER 2

LITERATURE REVIEW

2.1 INTRODUCTION TO METAL MATRIX COMPOSITES

The potential for extensive application of cast composites is very

large in India especially in areas of transportation, energy and

electromechanical machinery. The extensive use of composites can lead to

large savings in materials, energy and in several instances reduce

environmental pollution. Considerable progress has been made in the field of

cast metal matrix composites since cast aluminium-graphite particle

composites were first synthesized in 1965. Stir casting and pressure

infiltration have emerged as the two major processes to make composites.

Metal matrix composites in general consist of continuous or discontinuous

fibers, whiskers or particulates dispersed in a metallic alloy matrix. These

reinforcements provide the composite with properties not achievable in

monolithic alloys (Pradeep Rohatgi 1993).

According to Surappa (2003), the major advantages of Aluminium

Matrix Composites (AMCs) compared to unreinforced materials are as

follows:

Greater strength

Improved stiffness

Reduced density(weight)


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Improved high temperature properties

Controlled coefficient of thermal expansion

Thermal/heat management

Enhanced and tailored electrical performance

Improved abrasion and wear resistance

Control of mass (especially in reciprocating applications)

Improved damping capabilities.

2.2 MANUFACTURING OF METAL MATRIX COMPOSITES

Harris (1988) classified fabrication techniques into two broad

categories namely solid phase fabrication methods and liquid phase

fabrication methods. Solid phase fabrication methods include diffusion

bonding, hot rolling, extrusion, powder metallurgy, pneumatic impaction, etc.

Liquid-phase fabrication methods include liquid metal infiltration, squeeze

casting, compo casting, pressure casting, spray co deposition, stir casting etc.

The liquid metallurgy techniques are the least expensive and the multi step

diffusion bonding techniques may be the most expensive.

2.2.1 Stir Casting

This process involves incorporation of ceramic particulate into

liquid aluminium melt and allowing the mixture to solidify. The crucial thing

is to create good wetting between the particulate reinforcement and the liquid

aluminium alloy melt. The simplest and most commercially used technique is

known as vortex technique or stir casting technique. In this method the matrix

material is melt and stirred vigorously to form a vortex at the surface of the

melt. The vortex technique involves the introduction of pre-treated ceramic

particles into the vortex of molten alloy created by the rotating impeller.


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Stirring is continued for few minutes before the slurry is cast (Hai Zhi Ye and

Xing Yang Liu 2004). Stirring helps in two ways: (a) transferring particles

into the liquid metal and (b) maintaining the particles in a state of suspension.

It is then poured into the die and allowed to solidify. Mechanical stirring in

the furnace is a key element of this process. The resultant molten alloy, with

ceramic particles, can then be used for die casting, permanent mold casting, or

sand casting.

A homogeneous distribution of secondary particles in the

composite matrix is critical for achieving a high strengthening effect because

an uneven distribution can lead to premature failures in both reinforcement-free and reinforcement-rich areas. The reinforcement-free areas tend to be

weaker than the other areas. Under an applied stress, slip of dislocations and

initiation of microcracks can occur in these areas relatively easily, eventually

resulting in failure of the material. Microstructural inhomogeneties can cause

notably particle agglomeration and sedimentation in the melt and

subsequently during solidification. In the areas of signi cant segregation or

agglomeration of normally highly brittle hard particles, weak bonds are

formed in the material which can lead to the reduced mechanical properties. A

major concern associated with the stir casting process is the segregation of

reinforcing particles caused by surfacing or settling of the reinforcement

particles during the melting and casting processes.

Inhomogeneity in reinforcement distribution in these cast

composites could also be a problem as a result of interaction between

suspended ceramic particles and moving solid-liquid interface during

solidification. The nal distribution of the particles in the solid depends on

material properties and process parameters such as the wetting condition of

the particles with the melt, strength of mixing, relative density, and rate of

solidi cation. The distribution of the particles in the molten matrix also


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depends on the geometry of the mechanical stirrer, stirring parameters,

placement of the mechanical stirrer in the melt, melting temperature, and the

characteristics of the particles added.

Generally it is possible to incorporate upto 30% ceramic particles in

the size range 5 to 100 m in a variety of molten aluminium alloys. The melt

ceramic particle slurry may be transferred directly to a shaped mould prior to

complete solidification or it may be allowed to solidify in billet or rod shape

so that it can be reheated to the slurry form for further processing by

technique such as die casting, and investment casting. The process is not

suitable for the incorporation of sub-micron size ceramic particles orwhiskers. (Surappa 2003).

An interesting recent development in stir casting is a two-step

mixing process. In this process, the matrix material is heated to above its

liquidus temperature so that the metal is totally melted. The melt is then

cooled down to a temperature between the liquidus and solidus points and

kept in a semi-solid state. At this stage, the preheated particles are added and

mixed. The slurry is again heated to a fully liquid state and mixed thoroughly.

The resulting microstructure has been found to be more uniform than that

processed with conventional stirring. The effectiveness of this two-step

processing method is mainly attributed to its ability to break the gas layer

around the particle surface. Compared with conventional stirring, the mixing

of the particles in the semi-solid state can more effectively break the gas layer

because the high melt viscosity produces a more abrasive action on the

particle surface. Hence, the breaking of the gas layer improves the

effectiveness of the subsequent mixing in a fully liquid state.

In principle, stir casting allows for the use of conventional metal

processing methods with the addition of an appropriate stirring system such as

mechanical stirring; ultrasonic or electromagnetic stirring; or centrifugal force


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stirring. The major merit of stir casting is its applicability to large quantity

production. Among all the well-established metal matrix composite

fabrication methods, stir casting is the most economical (Compared to other

methods, stir casting costs as little as one third to one tenth for mass

production. For that reason, stir mixing and casting is now used for large-

scale production of Metal Matrix Particulate Composites. Various metals such

as Al, Mg, Ni, and Cu have been used as the matrix and a wide variety of

reinforcements like SiC, graphite, SiO2, Al2O3Si3N4, and ZrSiO4, have been

used as reinforcements. Processing of metal matrix composites by stir mixing

and casting requires special precautions including temperature control and

design of pouring and gating systems (Pradeep Rohatgi 2001).

2.3 RULE OF MIXTURES

Most studies concerned with the evaluation of mechanical

behaviour of composites use "Rule-Of-Mixtures"(ROM) to predict and/or to

compare the properties of the composite. ROM is an operational tool that uses

weighted volume average of the component properties in isolation to obtain

the magnitude of property for the composite.

2.4 MECHANICAL PROPERTIES AND DISTRIBUTION OF

REINFORCEMENT IN ALUMINIUM COMPOSITES

MMC materials have a combination of superior properties than

unreinforced matrix like increased strength, higher elastic modulus, higher

service temperature, improved wear resistance, high electrical and thermal

conductivity, low coefficient of thermal expansion and high vacuum

environmental resistance. These properties can be attained with proper choice

of the matrix and reinforcement.


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Fogagnolo (2004) produced aluminium matrix composite materials

reinforced with Silicon Nitride, Aluminium Nitride and Zirconium di Boride

by powder metallurgy and observed uniform distribution of reinforcement.

Mechanical alloying increased the tensile strength and powder hardness when

compared with unreinforced aluminium alloy. Addition of reinforcement

improved the ultimate tensile strength and hardness of the extruded materials.

Increase in composition of SiC in aluminium matrix increased the

hardness, impact strength and normalized displacement (Manoj Singla et al

2009). Homogenous dispersion of SiC particles in the Al matrix showed an

increasing trend in the samples prepared by two step stir casting technique.

Zhou and Xu (1997) produced two different aluminium matrix

composites (A356 and 6061) reinforced with SiC particles by gravity casting

and reported that a two-step mixing method improved the wettability of the

SiC particles and ensured good particle distribution. SiC particles are located

predominantly in interdendric regions as substrates of Si crystals in

(A356-10%SiC) composites. Arda Cetin and Ali Kalkanli (2008) observed

that addition of Mg in alloy improved the wettability of SiC particles.

Tamer Ozben et al (2008) examined the effect of SiC reinforcement

in aluminium (Al/7Si/2Mg) and observed that an increase in SiC increased the

tensile strength, hardness and density of Al/SiC composites, the impact

toughness decreased with increase in SiC particles. Machinability of MMC

was very less compared to traditional materials because of the abrasive

reinforcement element.

Bayraktar et al (2008) studied the damage mechanism of

SiCp/aluminium composites in as received and heat treated conditions of the

composites fabricated with different production methods. The crack initiated

at the interface (SiC/matrix) with large debonding at the interface between the


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SiC particles and the matrix causes reduced fatigue strength. The mechanical

behaviour of these composites was related to the particle geometry (shape),

distribution and size of reinforcement particles in the matrix.

Chennakesava Reddy and Essa Zitoun (2010) reported that the

yield strength, ultimate strength, and ductility of Al/SiC metal matrix

composites are in the descending order of Al 6061, Al6063 and Al 7072

matrix alloys. The contents of alloying elements such as Si, Fe, Mg and Cu

play a vital role in the mechanical properties Al/SIC composites. Mg

improved the wettability between Al and SiC particles by reducing the SiO2

layer on the surface of the SiC. The fracture modes of composites are ductilein nature.

Hamouda et al (2007) reported that the tensile strength and youngs

modulus of silicon dioxide particulate reinforced LM6 aluminium alloy

composites decreased gradually with increase in silicon dioxide. This was due

to the dominating nature of the compressive strength of quartz particulate

reinforced in LM6 alloy matrix.

Tensile strength, impact strength and fatigue properties of

aluminium composites reinforced with longitudinal steel fibers are higher

compared to composites reinforced with transverse fibers (Agbanigo and

Alowode 2008). This was due to the fact that transverse fibers created areas of

stress concentration which aids initiation and propagation of cracks resulting

in early commencement of deformation and fiber matrix debonding.

Fracture behaviour of two MMC materials Al6061/Al2O3and Al-Si

alloy SiC were studied by Perez Ipina et al (2000). Annealing heat treatments

promoted an increase in fracture toughness and observed formation of fatigue

precracking after heat treatment.


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Cepeda-Jime Nez et al (2008) developed a multilayered composite

laminate of Al 7075 and Al 2024 alloys by hot roll bonding with high impact

toughness. A post rolling tempering reduced the stresses around the interfaces

and optimized the precipitation hardening during T6 treatment. The

mechanism of interface pre-delamination was responsible for delamination

and crack nucleation in every layer of the composite laminate.

Wang Weimin et al (2002) fabricated (TiB2-Al

2O

3)/Al composites

by self-propagating, high temperature synthesis and hot pressing. The

fabrication processes parameters had a great influence on the ignition

temperature of synthesis reaction, reaction temperature and density of thesynthesized products. The fracture toughness increased rapidly with increase

in Al content in composites. The bending strength increased with increase in

Al content till about 30 vol% and then decreased with further increase in Al

content.

Roy et al (2006) produced Al based composites reinforced with

Fe-aluminide and alumina by in-situ process and observed that the initiation

temperature of in-situ reaction decreased significantly with the use of

nano sized Fe2O3crystallites. Evolutions of reinforcements are favoured by

the increase in pressing temperature.

Adamiak (2006) added titanium aluminide intermetallics particles

to aluminium matrix composites by hot extrusion and found that the addition

of intermetallic reinforcement particles to the composites do not influence

their tensile properties. The higher reinforcement content resulted in higherparticle dispersion hardening.

Veeresh Kumar et al (2010) were successful in adopting liquid

metallurgy technique in preparing Al6061-SiC and Al7075-Al2O3composites

and found that Al6061-SiC composites exhibited superior tensile strength


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properties than that of Al7075-Al2O3composites. The wear resistance of the

composites are higher, SiC significantly improved the wear resistance of

composites than Al2O3composites.

Neelima Devi et al (2011) found that the weight to strength ratio of

aluminium silicon carbide composite was about three times than that of mild

steel. Aluminium silicon carbide alloy composite material was two times less

in weight than aluminium for the same dimensions.

Abouelmagd (2004) reinforced different weight fractions of Al2O3

and Al4C3particles in pure aluminium by powder metallurgy. Hardness and

compressive strength improved to about four times by the addition of Al 2O3

and Al4C3. Addition of Al4C3 caused the ductile to brittle transition

phenomenon and showed large number of cracks. The crack width increased

with increase in deformation temperature.

Wodarczyk-Fligier et al (2010) observed uniform distribution of

boron nitride in aluminium matrix. Hardness of composite materials increased

with increase in boron nitride. Precipitation hardening caused an additional

increase in hardness of composite materials. Addition of boron nitride

decreased the tensile strength and corrosion resistance of composites.

Hardness of Al6061 aluminium composite increased with increase

in addition of frit particles (Ramesh et al 2010). Addition of frit particles

significantly improved the ultimate tensile strength and compressive strength

of Al6061 initially. Ultimate tensile strength of composites decreased above

the addition of 6wt % of frit particles. Above 8 wt % of frit the compressive

strength of composites decreased with increase in frit particles.


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2.5 FLY ASH AS REINFORCEMENT IN ALUMINIUM

COMPOSITES

Fly ash, being a waste material formed as a result of coal combustion in

power and metallurgical plants needs ecological processing to avoid its

dumping in waste grounds or landfills. In view of the combination of physical

and chemical properties and from the economical and ecological standpoint,

fly ash may be an attractive material as reinforcement in metal matrix

composites. Metal matrix composites manufactured by dispersing coal fly ash

in aluminum alloys improved the mechanical properties and wear resistance.

Babu Rao et al (2010) presented that fly ash can be classified into

two types namely the precipitator and cenosphere. The solid spherical

particles of fly ash are called precipitator fly ash and the hollow particles of

fly ash with density less than 1.0 g/cm3 are called cenosphere fly ash.

Addition of precipitator fly ash particles in aluminium alloy improved the

stiffness, strength and wear resistance. However addition of fly ash decreased

the density of composites. Cenosphere fly ash consisting of hollow fly ash

particles can be used for the synthesis of ultra light composite materials due to

its low density. Fly ash mainly contains elements like oxygen, silicon,

aluminium, iron, calcium, magnesium, sodium, potassium and titanium.

Incorporation of fly ash particles in aluminium alloy promotes the use of fly

ash and has the potential for conserving energy intensive aluminium, thereby

reducing the cost of aluminium products.

Rohatgi et al (2006) reported that incorporating fly ash into

aluminium castings decreased the energy content, material content, cost and

weight. Fly ash was incorporated in aluminium alloy matrix using stir casting

and pressure infiltration techniques. The sand and permanent mold castings

demonstrated adequate castability of aluminium melts containing up to 10 %

by volume of fly ash particles. The density and coefficient of thermal


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expansion of castings decreased with increase in fly ash content. The hardness

and wear resistance increased as the fly ash content increased. Tensile

strength of heat treated composites (T6) containing less than 8 vol% fly ash

was similar to that of the aluminium alloy.

LI Yue-ying et al (2007) investigated the mechanical behaviours of

Al/fly ash particles synthesized by squeeze casting method. The hardness of

the composites was higher than that of the Al matrix and increased with

increase in volume fraction of fly ash particles. The tensile strengths and

elongation of composites are lower than that of the Al matrix and decreased

with increase in volume fraction of fly ash particles.

Rohatgi et al (2005) observed that the presence of fly ash

cenospheres in pure Al matrix decreased the coefficient of thermal expansion.

Increase in applied pressure and infiltration time decreased the coefficient of

thermal expansion. Increase in infiltration pressure and temperature improved

the infiltration and decreased the entrapment of air voids.

Differential thermal analysis study by Guo et al(1998) indicated

that pressure infiltrated aluminium with 40 vol.% fly ash composite was

chemically stable after holding for 10 hrs at 850C enhancing the chemical

stability of aluminium-fly ash composites during synthesis and reheating.

Yadong Li et al (1998) combined polyethylene terephthalate plastic

waste with fly ash and observed that fly ash served as a filler element. Fly ash

particles served as a heat conductor, decomposition inhibitor and as

lubricating agent. Fly ash improved the compressive strength, melting and

mixing processes. Sobczak et al (2003) observed oxy-redox reactions between

Al and fly ash constituents such as SiO2, Fe2O3, Fe3O4and mullite resulting in

the formation of a thick reaction product region.


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Zuoyong Dou et al (2007) used fly ash particulates to produce

aluminium matrix composites and found that the Electro Magnetic

interference Shielding Effectiveness (EMSE) of aluminium improved with

increasing frequency. At higher frequency the EMSE properties of the

composites was similar to that of the aluminium alloy.

Rohatgi et al (2006) synthesized A356fly ash cenosphere

composites using gas pressure - infiltrated technique and observed the

presence of voids in regions where cenospheres are very close to each other.

The stress strain curves of composites showed a stress plateau region, which

was commonly observed in foam materials. The compressive strength, plateaustress and modulus of the composites increased with increase in density.

The damping properties of the hollow sphere fly ash/6061Al

composites with different fly ash diameters was measured by Wu et al (2006)

using forced vibration mode and bending vibration mode. The damping

capacity of fly ash/Al composite with smaller fly ash diameter was higher

than composite with larger fly ash diameter in both vibration modes.

The effect of three different stir casting routes on the structure and

properties of fine fly ash particles reinforced Al/7Si/0.35Mg alloy composite

was evaluated by Rajan et al (2007). Squeeze casting technique resulted in a

well dispersed and relatively agglomerate and porosity free fly ash particle

dispersed composites compared to liquid metal stir casting, compo casting,

modified compo casting and squeeze casting routes.

Wang Deqing et al (2001) employed squeeze infiltration process to

synthesize lead fly ash composite and found the external composite surface

consist a layer of pure lead. Corrosion testing indicated that the corrosion

resistance of the composite has improved.


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Bienias et al (2003) reported that the addition of fly ash particles in

aluminium by squeeze casting technology was advantageous in comparison

with gravity casting for obtaining higher structural homogeneity with

minimum porosity, good interfacial bonding and uniform distribution of fly

ash particles.

Mahendra and Radhakrishna (2007) observed uniform distribution

of fly ash in Al/5Cu alloy. The fluidity and density of the composites

decreased, the hardness increased with increase in percentage of fly ash

particulates. The tensile strength, compression strength and wear resistance

increased with increasing percentage of fly ash particulates. The slurryerosive wear resistance increased with increasing fly ash content. Corrosion

increased with increase in percentage of fly ash content.

Rohatgi et al (2002) observed aluminium fly ash composites have

higher specific strength and specific hardness compared to aluminium.

Hardness of the composite was higher than that of aluminium alloy.

No significant change in the aging kinetics was observed due to the presence

of spherical fly ash particles in the composite. Aging times of the order of

104 to 105 seconds was required to reach the peak hardness and improved

compressive strength.

2.6 THEORY OF WEAR

Wear behaviour is the surface damage or removal of material from

one or both of the two solid surfaces in sliding, rolling or impact motions

relative to one another. Wear is usually a progressive loss of weight and

alteration of dimensions over a period of time. Wear is an undesirable product

in almost all machine applications such as bearing seals, gears and cams etc.

Wear of components ranges from mild polishing type attrition to rapid and

severe removal of material.


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2.6.1 Types of Wear

In most basic wear studies dry friction was investigated to avoid the

influence of fluid lubricants. Dry friction is defined as the friction under

unlubricated conditions generally lubricated by atmospheric gases especially

oxygen. Wear can be classified as follows:

Abrasive wear

Adhesive wear

Corrosion wear

Erosive wear

Fatigue wear

2.6.1.1 Abrasive Wear

Abrasive wear occurs when asperities of rough, hard surface or

hard particles slides on a softer surface and damage the interface by plastic

deformation or fracture. In ductile materials with high fracture toughness the

hard asperities or hard particles results in plastic flow of the softer material.

Abrasion can be generally classified into two body or three body abrasions.

2.6.1.2 Adhesive Wear

Adhesive wear occurs when two smooth flat bodies are in slidingcontact either in lubricated or unlubricated conditions. Adhesion (or bonding)

occurs at the asperity contacts and these contacts are shared by sliding

resulting in detachment of a fragment from one surface and attachment to the

other surface.


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2.6.1.3 Corrosive Wear

Most of the metals are thermodynamically unstable in air and reacts

with oxygen to form oxide developing oxide layers on the surface of metal

when their interfacial bonds are poor. Corrosion wear is the gradual eating

away or deterioration of unprotected metal surfaces by the effects of the

atmosphere, acids, gases, alkalis, etc. This type of wear creates pits and

perforations and may eventually dissolve the metal parts.

2.61.4 Erosive Wear

Erosive wear is caused by the impact of particles of solid or liquid

against the surface of an object. The impacting particles gradually remove

material from the surface through repeated deformations and cutting actions.

It is a widely encountered mechanism in industry. The rate of erosive wear is

dependent on factors such as their shape, hardness, impact velocity and

impingement angle with the properties of the surface being eroded.

2.6.1.5 Fatigue Wear

Surface fatigue is a process by which the surface of a material is

weakened by cyclic loading. Fatigue wear is produced when the wear

particles are detached by cyclic crack growth of micro cracks on the surface.

These micro cracks are either superficial cracks or subsurface cracks.

2.7 WEAR BEHAVIOUR OF ALUMINIUM COMPOSITES

Aluminium based metal matrix composites have found application

in manufacturing various automotive engine components such as cylinder

blocks, pistons and piston insert rings where adhesive wear (dry sliding wear)

is a predominant process (Deuis et al 1996). Materials possessing high wear

resistance (under dry sliding conditions) are associated with a stable tribo


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layer on the wearing surface and the formation of fine equiaxial wear debris.

The influence of applied load, sliding speed, surface hardness, reinforcement

fracture toughness and morphology were critical parameters for adhesive

wear in relation to the wear regime encountered by the matrix material.

Sannino and Rack (1995) in their review on discontinuously

reinforced aluminium composites proposed that metals undergoing dry sliding

can be independently optimized through investigation of (i) third body

behaviour: the rate of third body ejection depends on sliding velocity, load,

geometry of contact and the reinforcement characteristics (ii) Surface

behaviour where adhesion is the principal debris generation mechanism (iii)Subsurface behaviour when delamination is the principal debris generation

mechanism.

2.7.1. Effect of Aluminium Matrix on Wear

The dry sliding wear behaviour of four aluminium alloys A2124,

A6092 (both precipitation hardened), A3004 (dispersion hardened) and

A5056 (work hardened) was investigated by Ghazali et al (2005) against M2

steel counter face in the load range of (23140) N and at a fixed sliding speed

of 1 m/s. Severe wear was observed for all alloys, with specific wear rates in

the range of 0.3110 4 to 4.2310 4 mm3/ (N m). The dry sliding wear

resistance of wrought aluminium alloys was strongly influenced by the alloy

composition mainly due to the differences in the hardness and the chemical

interaction with the counter face. Wear was dominated by the transfer of Fe

from the counter face for all alloys and resulted in the formation of a

Mechanically Mixed Layer (MML). Linear relationship between specific

wear rate and thickness of the MML was observed for A2124, A5056 and

A3004 alloys.


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Rajaneesh et al (2011) explored the wear behaviour of Zinc/

Aluminium alloy composite reinforced with SiC (30 ) particulate produced

using liquid metallurgy technique. The sliding speed was varied between 1.2

m/s to 5.1 m/s and load was varied between 10 N to 40 N. Wear rate of

composites increased with increasing load and increasing speed. Zinc based

MMC showed lower co-efficient of friction under dry sliding condition. The

presence of SiC restricted the growth of micro cracks and delamination.

Combination of delamination and abrasive wear was observed during the test.

Adhesion and melting of the specimen was also observed.

Anasyida et al (2010) found that the addition of cerium inAl/12Si/4Mg lead to the precipitation of intermetallic compound in needle

like structures in wear test conducted in dry conditions at room temperature of

25oC. Increasing cerium content up to 2 wt% improved both wear resistance

and micro hardness of the aluminium alloy. Addition of more than 2 wt%

cerium decreased the micro hardness resulting in low wear resistance.

Formation of craters and severe localised plastic deformation were observed

on the worn surface of alloys with higher Ce content. The mechanism of wear

was a combination of abrasion and adhesion.

Tribological behaviour of Al (8090)/Li and Al/Li/15% SiC

composite was analysed by Rodriguez et al (2006). Transition from mild wear

to severe wear, dependent on nominal pressure was observed in both materials

leading to changes of two orders of magnitude in wear rate. The formation of

Mechanically Mixed Layer (MML) was a key factor in controlling the mild

wear of these materials. The morphology and composition of the wear debris

also changed with the wear mechanism.

Ramachandra, Radhakrishna (2006) in their study on aluminium

matrix composites reinforced with silicon carbide (SiC) particulates using

conventional vortex casting technique reported that the slurry erosive wear


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resistance increased with increase in SiC content. The formation of passive

layers on the surface of slurry erosive specimens decreased the wear loss by

forming protective layers against the impact of slurry.

2.7.2 Effect of Reinforcement on Wear

Feng Tang et al (2008) conducted pin-on-disk dry sliding wear tests

at sliding speeds ranging from 0.6 to 1.25 m/s and under loads ranging from

3.98 to 6.37MPa for pin specimens of Al-5083 matrices composites

reinforced with 5 and 10 wt.% B4C particles. Two stages in the pin length

reduction curves while reinforcing B4C in aluminium alloy was observed. The

low length reduction rate in the first stage corresponded to a flat stage with

low coefficient of friction. The transition from the first stage to the second

stage attributed to the change in wear mechanism from abrasive wear to

adhesive wear.

Jha et al (1989) studied the dry sliding wear of 6061 aluminium

alloy and composites containing graphite particle dispersions developed by

power metallurgy route. The wear rate of composites increased with

increasing amount of graphite due to the increased porosity (interconnected

and interfacial) in the composites. Most of the wear debris was flaky in

nature. Mandal et al (2007) reported that TiB2particles improved the wear

performance of the Al/4Cu alloy. The wear resistance increased with increase

in amount of TiB2. The improvement in wear resistance of both alloy and

composites was mainly due to the formation of finer debris.

Pritt Kulu et al (2005) reported the behaviour of powder materials

and coatings under different abrasive wear conditions was dependent on the

type, composition of materials and conditions of abrasive wear (abrasive

particle size and velocity, media of abrasive wear etc). Under high-energy

impact wear TiC based cermets with optimal composition were almost as


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good as hardmetals. The wear resistance of sprayed coatings at impact wear is

low due to their low thickness.

2.7.3 Effect of Manufacturing Processes on Wear

Das (2004) reported aluminium (LM13)/ SiC composite developed

by (stir casting or vortex technique) exhibited uniform distribution of the

particle in the matrix and good interface bonding between the ceramic phase

and the metallic matrix. Beyond a critical load and abrasive size, the Al alloy

SiC composite exhibited more or less the same wear rate compared to that of

aluminium alloy. Wear rate increased almost linearly with applied load.

Composites exhibited improved wear resistance and seizure pressure

compared to that of aluminium alloy under both dry and lubricated sliding

wear. The corrosion resistance of composite was comparatively higher than

the base alloy irrespective of the corrosive media.

Walker et al (2005) reinforced 15 vol.% of SiC particles in

aluminium alloy (2124, 5056) by powder metallurgy route. Mild wear was the

predominant wear mechanism during lubricated sliding. Two and three body

abrasives from the counter face deformed the surface by micro ploughing and

indentation. Silicate particles exceeded their fracture toughness under the

applied contact stress and liberated small particles as debris.

Dobrzanski et al (2010) reinforced EN AC - AlSi12 alloy matrix

with Al2O3preforms by pressure infiltration and observed numerous visible

scratches on the disc caused by the pull out of Al2O3 particles from the

matrix. If the process of infiltration was complete, all pores are fulfilled with

liquid matrix material.

Vieira et al (2009) studied the unlubricated sliding wear of

centrifuged Al alloy and Al/SiCp Functionally Graded Metal (FGM) matrix


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composites processed with different centrifugal speeds. FGM cast at low

centrifugal speed (1500 rpm) presented a smooth gradient on SiCp

distribution while FGM cast at higher centrifugal speed (2000 rpm) revealed a

sharper gradient on the distribution of reinforcing particles.

In situ micro alloying of aluminium alloy (2014) with Sn and Ag

was conducted by Bishop et al (1998) using reaction sintering technique.

Using this method, samples were microalloyed with either Sn or Ag, aged to

peak hardness, and subjected to dry sliding wear tests in accordance with

ASTM standards. Sn and Ag micro alloyed samples developed improved

wear resistance with sintering time due to an increased extent of microalloying.

2.7.4 Effect of Reinforcement Orientation on Wear

The sliding wear behaviour of preferred orientation of SiC whiskers

in an alumina based ceramic cutting tool material was studied by Hong Xiao

et al (1991). The surface parallel to hot pressing direction was found to have

more wear resistant than the surface perpendicular to hot pressing direction.

Oxidation of Sic whiskers occurred in the wear process which accelerates the

wear rate. The oxidation of whiskers is less on the surface parallel to hot

pressing direction.

The friction and wear behaviour of aluminium/graphite fiber

composites was examined by Nayeb Hasbemi (1991) as a function of

interfacial reaction. The wear fibers parallel to the sliding direction were

dominated by three wear mechanisms: (1) matrix removal by delamination (2)

wear due to ploughing and (3) fiber pull-out. Whenever fiber pull-out was a

contributing mechanism in the wear, the wear rate is an exponential function

of the normal load. In contrast, the wear rate of composites was proportional

to the normal load in the absence of fiber pull-out. When the fibers were


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normal to the sliding plane and direction, fiber pull-out was minimal. When

the fibers were parallel to the sliding plane and perpendicular to the sliding

direction, fiber roll-out was significant. When the fibers were parallel to the

sliding plane and direction, fiber pull-out was significant.

Nannaji Saks and Nelson K. Szeto (1992) compared the wear

behaviour of three composites namely graphite /aluminium, stainless steel

/aluminium and Al2O3/Al/Li and reported that graphite/Al is a low-friction,

low-wear composite. Stainless steel/Al is a high-friction, high-wear and

highly anisotropic composite. The low friction was due to spreading of

graphite at the sliding interface. Fiber pull-out was the dominant mechanismof wear, especially in the Gr/Al and SS/Al composites. Poor bonding and

fiber clusters lead to high wear and high friction.

The wear and frictional behaviour of LM 13 alloys containing up

to 30 vol % of Al2O3 fiber were investigated by Akbulut (1998) in sliding

against a hard steel counter face (63 HRC) under dry conditions at room

temperature in the transverse section of composites. Increased fiber volume in

the composites decreased the wear rate and coefficient of friction. Reinforcing

AI-Si (LM 13) alloy with alumina short fibers reduced the wear rate of the

matrix alloy by a factor from 1.2 to 4.o and the coefficient of friction by 5-

25% , depending on the fiber volume. Excessive plastic deformation occurred

during the wear and the amount of the plastic deformation decreased with

increasing fiber volume.

Iwai et al (2000) reinforced Al2O

3fibers ranging from 0.03 to 0.26

volume fractions and rubbed against a pin of nitrided stainless steel with a

load of 10 N at a sliding velocity of 0.1 m/s in aluminium alloy. Improvement

in dry sliding wear resistance of composites was observed. Reinforcements

inhibited plastic flow and restricted propagation of wear cracks. Duration of

severe wear regime and severe wear rate decreased with increase in fiber


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volume fraction. Wear rate of the counter face (steel pin) increased

moderately with increase in volume fraction of alumina fibers.

2.7.5 Effect of Sliding Speed on Wear

Uyyuru et al (2007) studied the tribological behaviour of stir cast

Al/Si/SiCp composites against automobile brake pad material. With increase

in applied normal load and sliding speed (1.5, 3, 4 m/s) the wear rate

increased, the coefficient of friction decreased with increase in applied normal

load and sliding speed. Heterogeneous type of tribo layer was observed over

the worn disc surfaces which affects the wear behaviour apart from acting as a

source of wear debris.

Singh et al (2001) studied the effect of granite reinforcement (10

wt.%) on dry sliding wear behaviour of aluminium silicon alloy (LM6)

manufactured by liquid metallurgy technique. Increase in sliding speed (1.89,

3.96 and 5.55 m/s) decreased the wear rate initially and then increased with

sliding speed in case of aluminium alloy. On the contrary, wear rate decreased

with sliding speed for the composite except at the maximum sliding speed and

at high pressures. Frictional heating and friction coefficient were more in case

of the matrix alloy than that of the composite. The composite seized at much

higher temperature than that of the matrix alloy.

Prasanna Kumar et al (2006) studied the wear behaviour of

zinc/aluminium alloy composites reinforced with garnet particles (0, 5, 10,15

and 20 %) fabricated by liquid metallurgy. The wear loss of composites was

less than that of the alloy and increased with increase in load and sliding

speed (upto 3.65 m/s). The wear resistant increased with increase in garnet

content. The coefficient of friction of zinc/aluminium alloy metal matrix

composite decreased with increase in percentage of garnet particles. The


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friction coefficient of zinc-aluminium alloy metal matrix composite decreases

with increase in percentage of garnet from 0 % to 20 % by weight.

2.7.6 Effect of applied load on wear

The wear rate of composites was lower than that of Al 2219

aluminium alloy and decreased with increase in SiC content. With an increase

in load (0 to 60 N) , cracking of SiC particles occurred and a combination of

abrasion, delamination and adhesive wear was observed (Basavarajappa et al

2006). Mild wear was observed for a small applied load, but as the load

increased up to 20 N, the wear rate of the unreinforced alloy and composite

increased. At the load of 20 N, the wear pattern changed for the unreinforced

alloy, while the composite followed the same trend up to 50 N (the

unreinforced alloy seizes at this load). At a 60 N load, the SiCp reinforced

composites showed a change in the wear rate pattern to severe wear.

Mehmet Acilar and Ferhat Gul (2004) carried sliding wear tests

under normal loads of 12, 24 and 36 N at a sliding speed of 1.0 m/ s and

sliding distances of 2.2, 3.6 and 5.0 km against a steel disk using a pin-on-disc

type apparatus. The surface damage of Al/10Si/SiCp (10 and 30-vol% )

composites produced by vacuum infiltration technique increased with

increasing load since matrix materials have wear low resistance. Delamination

type of wear mechanism was observed under higher loads. Oxidation was the

wear mechanism under the low load, since oxide layer with high Fe content

formed on the steel disc surface served as a lubricant and reduced the wear.

The damage to the surface of the composites increased with increasing load.

Shorowordi et al (2006) investigated the tribo surface

characteristics of two aluminium metal matrix composites reinforced with

B4C and SiC sliding against a commercial phenolic brake pad at different

pressures (0.75 to 3.00MPa). Wear rate and surface roughness of both MMCs


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increased with increase in contact pressures, the coefficient of friction

decreased at high contact pressure. The wear rate and coefficient of friction of

Al/B4C was lower than that of Al/SiC. The surface chemistry of the transfer

layer particularly the carbon percentage influenced the wear and coefficient of

friction.

2.7.7 Effect of Sliding Distance on Wear

Ramesh et.al (2005) observed that the increase in loads and sliding

distances (90-540 m) resulted in higher volumetric wear loss but lowered the

wear coefficient of Al6061/ TiO2composites. At larger sliding distances, rise

in temperature of the sliding surfaces resulted in softening of both the matrix

alloy and the composite pin surfaces, leading to heavy deformation at higher

sliding distances contributing to higher wear losses. The volumetric wear loss

of the composites were much lower when compared with the matrix alloy and

reduced with increased content of TiO2 in the composites at all sliding

distances studied. This is due to enhancement in hardness of the composites

resulting in improvement of wear and seizure resistance of materials.

Wear loss was found to increase more or less linearly with sliding

distance (125-500 m) for A6061 matrix alloy as well as composites

containing 7 vol.% graphite particles. The rate of increase in wear rate with

increase in sliding distance corresponding to the 6061 matrix alloy was less

than that of the graphite containing composite.

Wear rates and friction coefficients were measured by Martin

(1996) in 2618 Al alloy reinforced with 15 vol % SiC and the corresponding

unreinforced alloy in the temperature range 20- 200oC. Both materials

presented a transition from mild to severe wear as the temperature increased

with increase in sliding distance. The transition temperature was between 100


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and 150oC in the unreinforced alloy and between 150 and 200

oC in the

composite.

2.7.8 Effect of Environmental Conditions on Wear

Deuis et al (1998) formed composite coatings on composites

reinforced with discontinuous ceramic particles of Al2O3, SiC and TiC on

AA5083 aluminium alloy using plasma transferred arc (PTA) surfacing

technique and the specimens were subjected to dry and wet (liquid media

employed was either distilled water or a saline solution of 3.5 wt.% NaCl)

environments. Dry and wet abrasive wear studies were employed using

modified sand/rubber wheel abrasion tester. The wet environment promoted a

higher wear rate compared to the dry conditions. The wear environment

significantly influenced wear behaviour. Wet abrasion characterized by a

higher Np (function of wear scar length, peripheral wheel speed and Mp the

silica sand particle mass value) at the contact zone promoted a higher wear

rate compared to dry abrasion.

Rolf Wasche et al (2004) compared the friction and wear behaviour

of pressure-less sintered TiB2 and SiC against SiC and Al2O3 balls under

unlubricated conditions at room temperature. The coefficient of friction

against both ball materials decreased with increase in humidity against

alumina than against SiC. Wear rate was affected significantly by humidity

and decreased by the magnitude for Al2O3/SiC and SiC/SiC system.

Murthy et al (2004) reported that doping elements (Al, Mg and P)

reinforced with silicon carbide affected the coefficient of friction at low

humidity (30% RH) than at high humidity (60% RH). At higher humidity

coefficient of friction (COF) decreased but the effect of doping elements was

insignificant due to faster kinetics of tribo chemical reactions. Continuous


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adhesion, twisting and rolling of small wear particles during the wear process

resulted in the formation of long needle like debris.

2.7.9 Effect of Counter Face Material on Wear

Howell and Ball (1995) conducted wear test of magnesium/silicon

aluminium alloys reinforced with SiC (20 vol. % SiC) particulates against

automobile friction linings (brake pads). They revealed that if the structure

and composition of friction linings are arranged correctly, the wear resistance

and frictional properties of aluminium MMC brake rotors are superior to

those of cast iron brake rotors. At high loads and sliding velocities,

cohesiveness of materials within the pad was poor and the wear rate of the

MMC was extremely high.

Natarajan et al (2006) studied the wear behaviour of aluminium

metal matrix composite (A356/25SiCp) sliding against brake shoe lining

material and compared it with the conventional brake drum made of grey cast

iron. MMCs have considerable higher wear resistance than conventional grey

cast iron while sliding against automobile friction material under identical

sliding speed and load conditions.

Kok and Ozdin (2007) reinforced Al2O3(16m and 32m) in 2024

Al matrix alloy and observed significant improvement in abrasive wear

resistance of composites tested against different abrasives (600,320,240 grit).

Wear resistance increased with increasing Al2O3 particles content and

abrasive size and decreased with increasing the sliding distance, applied load

and abrasive grit size.

Straffelini et al (2004) studied the friction and wear behaviour of

aluminium based composites reinforced with SiC. The friction and wear

behaviour was connected with the characteristics of the transfer layer formed


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m/s). For unreinforced 6061 Al and A356 A1 alloys a transition from mild to

severe wear occurred in ranges of 175-190oC and 225-230 oC respectively.

With the addition of 20 vol. % Al203to 6061 Al, the mild wear transformed to

severe wear transition was raised to a range between 310-350 C. Likewise,

an addition of 20 vol. % of SiC to the A356 Al increased this transition to

440-450C. A hybrid A356 AI composite containing 20 vol. % SiC and 10

vol.% graphite remained in a mild wear regime at the highest test temperature

of 460oC. All the reinforced alloys were able to withstand considerable

thermal softening effects while remaining in a mild sliding we at regime. The

elevated temperature sliding wear of the particulate reinforced alloys was

accompanied by extensive thermal softening of their bulk matrix

microstructures. The formation of transfer layers of comminuted particulates

and steel inclusions delayed the onset of severe wear.

2.8 WEAR BEHAVIOUR OF ALUMINIUM/FLY ASH

COMPOSITES

Rohatgi and Guo (1997) observed that abrasive wear resistance of

aluminium alloy containing 5vol% fly ash was superior to that of the base

A356 alloy below a load of 8 N at a sliding velocity of 1 m/s. The decrease in

specific wear rate with increase in load was due to an accumulation of wear

debris in the interstices between the abrading particles and observed sub

surfaces below the rubbing surfaces of composites and the base alloy.

Samrat Mohanty and Chugh (2007) incorporated fly ash particles in

automotive brake lining friction composites. Ingredients such as phenolic

resin, aramid pulp, glass fiber, potassium titanate, graphite, aluminium fiber

and copper powder were used in the composite development phase in addition

to fly ash. The developed brake lining composites have exhibited consistent

coefficient of friction and wear rates.


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Mahendra and Radhakrishna (2005) produced Al4.5%Cu alloy fly

ash composite bush by stir casting technique. The bush made from the

composite showed more resistance to wear than the aluminium alloy under

lubricated conditions for 200 hours. A cylinder liner was cast from the

composite and then tested in a two stroke petrol engine. No seizure was

observed in the cylinder liner even after 400 hours of testing.

2.9 PROPERTIES OF ALUMINIUM HYBRID COMPOSITES

Naplocha and Granat (2008) reinforced Al2O3 and graphite in

monolithic Al/Si7 alloy and observed that alumina fibers considerably

improved the wear. Addition of graphite protected the composite from

seizure. The composite reinforced with graphite fibers was less sensitive to

applied load than composites reinforced with graphite flakes.

Satyappa Basavarajappa et al (2005) compared the wear behaviour

of aluminium alloy reinforced with SiCp and graphite. Incorporation of

graphite particles in aluminium composites decreased the wear rate. Seizure

occurred for aluminium alloy but not in Al/SiCp and graphitic composites.

Adel Mahamood Hassan et al (2009) investigated the effects of

adding copper and silicon carbide as reinforcement particles to Al/4Mg alloy.

Wear loss of alloys containing copper was less than that for the copper free

alloys. Addition of SiC in Al/Mg/Cu alloy decreased the wear rate, the

coefficient of friction values increased with increase in SiC.

Hayrettin Ahlatcia (2006) produced Al/Mg matrix hybrid

composites reinforced with Al2O3 and SiC by pressure infiltration. Matrix

hardness and compression strength increased while porosity and impact

toughness decreased with increasing Mg content. Wear resistance of the


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composites increased with increasing Mg addition. Abrasion resistance of the

hybrid composites decreased with increase in test temperature.

Umanath et al (2011) fabricated aluminium (Al6061) based hybrid

composites reinforced with mixtures of SiC and Al2O3by stir casting method

and found that the coefficient of friction and wear rate of the hybrid

composite was less compared to that of the matrix alloy, Al/SiC composite

and Al/Al2O3 composite.

Wilson and Alpas (1996) observed that addition of SiC and Al203to

6061 Al alloy improved the seizure resistance. Elevated temperature sliding

wear of particulate reinforced alloys was accompanied by extensive thermal

softening of their bulk matrix microstructures. Presence of graphite in hybrid

composite introduced greater mild wear losses due to increased contact

surface extrusion effects.

Dry sliding wear of AA6061 alloy reinforced with SiC particles and

metal coated carbon fibers was studied by Urena et al (2009). Composites

manufactured with duplex (SiC and carbon) reinforcements presented better

wear behaviour than composites reinforced with SiCp because of the lubricant

effect of carbon fibers.

Tribological behaviour of Al/Saffil/C hybrid composites with

graphite and alumina fibers produced by squeeze casting method was studied

by Naplocha, Granat (2008). Crushed graphite fibers and segments of alumina

fibers embedded in the matrix were observed. In composite with flake

graphite weak layers of the matrix broke and delaminated above a graphite

pocket.


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2.10 INFLUENCE OF PARTICLE SIZE ON COMPOSITES

Kassim et al (1999) investigated the two body abrasive wear

behaviour of aluminium matrix composites reinforced with silicon carbide

particles with mean sizes of 10 m, 27 m and 43 m fabricated by powder

metallurgy route. The abrasive wear resistance of composites against an

abrasive paper increased with increase in volume fraction and size of SiC

particles. The abrasion resistance decreased with increase in the relative

abrasive penetration depth until a critical value, abrasion resistance was

independent of the penetration depth.

Singh et al (2002) studied the two body abrasive wear behaviour

aluminium alloy/10 wt% sillimanite (Al2SiO5) particle composite against

emery papers of desired abrasive sizes fixed on a wheel. The wear rate

decreased with sliding distance and increased with increase in abrasive size

and applied load irrespective of the materials.

Sug Won Kim et al (2003) investigated the effects of alloying

elements and heat treatment of Al/Si/Cu/Mg/Ni alloy composites reinforced

with SiCp fabricated by a duplex process of squeeze infiltration (1st step)

followed by squeeze casting (2nd step). The hardness of the composites

increased with decrease in SiCp size and also with Ni addition. Al composite

reinforced with 10 m SiCp have the lowest wear amount compared to

composites with 3 m and 5 m SiCp composites.

Hayrettin Ahlatci et al (2001) investigated the abrasive wear

behaviour of pure aluminium composites reinforced with 13 m and 37 m

diameter SiC particles produced by pressure infiltration technique. Abrasive

wear tests carried out against Al2O3 revealed that the effect of SiC particles

size on the wear resistance of compacts depends on the size of the Al2O3


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abrasive grains being rubbed. The compact which had 13 m SiC particles

exhibited higher wear rate than the compact with 3 7m SiC particles.

Sudarshan and Surappa (2008) fabricated aluminium alloy (A356)

composites with narrow size range (53106 m) and wide size range

(0.5400 m) fly ash particles. Composites reinforced with narrow size range

fly ash particle exhibited superior mechanical properties compared to

composites with wide size range particles. At higher loads wear resistance of

composites reinforced with narrow size range fly ash particles was superior to

that of composites with wide fly ash particles.

2.11 REGRESSION ANALYSIS

Regression analysis is a statistical tool for the investigation of

relationships between variables. Regression analysis gives information on the

relationship between a response (dependent) variable and one or more

(predictor) independent variables to the extent of information contained in the

data. The goal of regression analysis is to express the response variable as a

function of the predictor variables. The duality of fit and the accuracy of

conclusion depend on the data used.

There are three types of regression. The first is the simple linear

regression. The simple linear regression is for modeling the linear relationship

between two variables. One of them is the dependent variable Y and another

is the independent variable X. The simple regression model is often written as

shown in Equation (2.1).

Y= 0+ 1x + (2.1)

where Y is the dependent variable, 0is Y intercept, 1 is the gradient or the

slope of the regression line, x is the independent variable, and is the random


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error. It is usually assumed that error is normally distributed with E( ) = 0

and a constant variance ( ) =2 in the simple linear regression. The term

linear is used because the Equation (2.1) is a linear function of the unknown

parameters 0and 1.

The second type of regression is the multiple linear regression with

one dependent variable and more than one independent variables. The

multiple linear regression assumes that the response variable is a linear

function of the model parameters and there are more than one independent

variables in the model. Equation (2.2) shows the general form of the multiple

linear regression models.

Y= 0+ 1x1............ pxp+ (2.2)

where Yis dependent variable, 0, 1, 2....... p are regression coefficients, and

x1,x2.xp are independent variables in the model. In the classical regression

setting it is usually assumed that the error term follows the normal

distribution with E( ) = 0 and a constant variance Var( ) =2.

The multiple linear regressions involve more issues than the simple

linear regression such as collinearity, variance inflation, graphical display of

regression diagnosis, and detection of regression outlier and influential

observation. A linear regression model may also be written as shown in

Equation (2.3).

Y= 0+ 1x1+ 2x2+ 12x1x2+ (2.3)

In the linear regression model Equation (5.3) a cross-product term,

x1x2 is included in the model. This term represents an interaction effect

between the two variables x1 and x2. Interaction means that the effect

produced by a change in the predictor variable on the response depends on the


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level of the other predictor variable(s). The third type of regression is

nonlinear regression, which assumes that the relationship between dependent

variable and independent variables is not linear in regression parameters.

Y= 0+ 1x1+ 2x12+ 3x3

2+ (2.4)

Equation (2.4) is also a linear regression model and is referred to as

a polynomial regression model. Polynomial regression models contain

squared and higher order terms of the predictor variables making the response

surface curvilinear. A second order model is the one in which the maximum

power of the terms in the model is two.

Few attempts have been made to model and predict the relationship

between two or more of process variables and a response variable in different

applications. Siva et al (2009) developed a mathematical model to correlate

the various process parameters of weld bead geometry in plasma transferred

hard facing of a nickel based alloy over stainless steel plates. Multiple

regression method was used by Vishal Parashar et al (2010) to formulate the

gap voltage, pulse on time and pulse off time to the material removal rate of

wire cut Electro Discharge Machining.

Delijaicov et al (2010) applied ANN and multiple regression

technique to a data set generated by shot peening with aluminium alloy plates.

Tensile strength of friction stir welded AA6061 aluminium alloy joints was

predicted by Elangovan et al (2009) incorporating welding parameters and

tool profiles using statistical tools such as design of experiments, analysis of

variance and regression analysis. Relation between machining forces and tool

wear of aluminium metal matrix composite was studied by Lin et al (2003)

using multiple regression analysis.


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Mondal et al (1998) studied the two-body abrasive wear behaviour

of a cast aluminium alloy/Al2O3 particle composite at different operating

conditions using factorial design of experiment and developed an empirical

linear regression equation for predicting wear rate within a selected

experimental domain. Kumar and Balasubramanian (2008) conducted wear

test and developed a mathematical model by Response Surface Method

(RSM), Analysis of Variance (ANOVA) technique was applied to check the

validity of the developed model and Students t-test was utilised to find the

significance of factors.

Sahin (2010) employed factorial design to describe the abrasivewear behaviour of Al alloy and its composites and to develop linear equations

for predicting wear rate within selected experimental conditions. Dobrzanski

et al (2010) worked out statistical models to determine the abrasive wear of

examined materials depending on the content of ceramic phase, friction

distance and load.

2.12 ARTIFICIAL NEURAL NETWORKS

Artificial Neural Network (ANN) usually called neural network is a

mathematical model or computational model that is inspired by the structure

and/or functional aspects of biological neural networks. Neural networks

consist of an interconnected group of artificial neurons and it processes

information using computation approach. Modern neural networks are non

linear statistical data modelling tools. They are usually used to model

complex relationships between inputs and outputs. In recent times Artificial

neural network (ANN) is being used as an alternate statistical method. It has

been applied successfully to different engineering problems.

Abdelhay (2002) examined the feasibility of using an integration

system between some measured ultrasound parameters from non destructive


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test (NDT) to determine the influence of grain size and carbon. Fadare et al

(2009) developed an ANN model to predict the tool life and wear rate while

machining Ti/6Al/4V alloy by varying the cutting parameters (cutting speed,

feed rate, depth of cut, coolant pressure, and tool type) using a three layered,

feed forward, back propagation artificial neural networks.

The machining forces-tool wear relationship of an aluminium metal

matrix composite was studied using multiple regression analysis (MRA) and

Generalised Radial Basis Function (GRBF) neural network by Lin et al

(2003). The use of a neural network analysis improved the accuracy of tool

wear prediction particularly when the functional dependency is non linear.Hulya Kacar Durmus et al (2006) studied the effects of wear loss and surface

roughness at various ageing temperatures, load, sliding speed and abrasive

grit diameter of aluminium alloy against SiC water proof emery using

artificial neural networks and observed that the experimental results coincide

with ANN results.

Mustafa Taskin et al (2008) used ANN approach to predict the

diffusion bonding behaviour of Ni/Ti alloys manufactured by powder

metallurgy process using back propagation neural network. In neural

networks training, different temperatures and welding periods were used as

input for predicting the shear strength. Rajendraboopathy et al (2008) was

successful in generating a feed forward back propagation neural network

model to predict the failure of fiber reinforced composite materials by

acoustic emission influenced by parameters like amplitude, duration, counts

and energy.

2.13 CONCLUSIONS BASED ON THE LITERATURE

An extensive literature was carried out to understand the basic

needs of aluminium based MMCs. This includes various aspects such as


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characterization, fabrication, testing, analysis and correlation between

microstructure and the properties.

The conclusions drawn from the study are

There exists a wide range of database in the literature for

different reinforcements in aluminium metal matrix

composites including hybrid composites. The mechanical

properties and wear behaviour of aluminium composites were

superior to their base alloy.

Studies revealed that wear and coefficient of friction ofcomposites are influenced by reinforcement content, sliding

speed and applied load. Reinforcement particle size was also a

factor influencing the wear and mechanical properties of

MMCs. Few literature were available on the impact of

reinforcement size on mechanical and wear behaviour of

composites.

In particle reinforced composites fracture mode was observedto depend on the reinforcement purity, reinforcement particle

size, nature of interface, volume fraction of reinforcement,

fabrication route adopted, heat treatment etc.

Different techniques were available for the production of

metal matrix composite. Some of the manufacturing processes

are far more expensive than others. Generally the manufacturer

prefers the lowest cost route for mass production. Therefore

stir casting technique represents a substantial proportion of

the MMCs in commercial sectors.


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Artificial Neural Networks and statistical modelling can be

used to predict the influence of parameters on process

variables.

Thus the priority of this work will be to prepare MMC using

fly ash (an industrial waste) as reinforcement in aluminium

(A380) matrix and to study its wear characteristics. Studies

were also to be carried on the influence of particle size on

mechanical properties and wear behaviour of aluminium/fly

ash composites.

Documents

7_chapter2 MMC