10

CHAPTER 2

LITERATURE SURVEY

2.1 INTRODUCTION

This chapter covers a literature review on the production as well as

evaluation of mechanical and tribological characteristics of Particulate

Aluminium Metal Matrix Composites (PAMCs). Furthermore, the review also

includes the use of Design of Experiments(DoE), statistical tools for

modelling and optimisation methods for arriving at the optimum performance

of the composites has been also covered in detail.

The earliest PAMCs date back to the late 1960s and early 1970s

with the production of Graphitic aluminium composites for automotive

pistons. Studies on PAMCs based on various aluminium alloys and

reinforcements have been taken up since. Universal series of wrought

aluminium alloys such as 1000 (Pure aluminium), 2000 (Al-Cu),

3000 (Al-Mn) 4000 (Al-Si), 5000 (Al-Mg) 6000 (Al-Si-Mg),

7000 (Al-Zn-Mg) and 8000 (Al-Li) have been used in the preparation of

PAMCs. Among the cast aluminium alloys, aluminium-silicon, aluminium-

copper and aluminium-magnesium alloy systems have been used extensively

in PAMCs applications. A summary of various aluminium alloys explored

are given in Table 2.1 and 2.2.

11

Table 2.1 Wrought aluminium alloys used as a matrix by previous researchers

Wrought Aluminium Alloy Reference

1060 Rosenberger et al. (2009)

1050 Lim et al. (1999)

1061 Rosenberger et al. (2005)

2024 Abdel-Azim et al. (1995), Narayan and Bai(1995), Kiourtsidis and Skolianos (2002), Kokand Ozdin (2007) and Rao and Das (2011)

2618 Mindivan et al. (2006)

2219 Basavarajappa et al. (2006)

2009 Sannino and Rack (1996) and Srivatsan et al.(2005)

2014 Alpas and Embury (1990), Srivatsan(1995),Modi (2001), Mallikarjuna et al. (2011)and Sahin and Kilicli (2011)

2124 Srivatsan (1992), Muratolu and Aksoy (2006)and Sukumaran et al. (2008)

2011 Sahin and Özdin (2008), Rao and Das (2011)and Sahin and Kilicli (2011)

6061 Jha et al. (1989), Zhang and Alpas (1993),Straffelini et al. (1997), Srivatsan et al. (2002),Yang (2003), Ganesan et al. (2005), SeyedReihani (2006), Yang (2007), Mahadevan et al.(2008), Urena et al. (2009), Kumar et al. (2010)and Ramesh et al. (2011)

6063 Natarajan et al. (2009)

6092 Wang et al. (2001), Salazar and Barrena (2004)and Ghazali et al. (2008)

7005 Ceschini et al. (2006)

7075 Kumar et al. (2010)

8090 Downes and King (1993), Bauri and Surappa(2008) and Rao et al. (2010)

12

Table 2.2 Cast aluminium alloys used as matrix by previous researchers

Cast Aluminium Alloy Reference

Pure Al Mandal et al. (2004

A206 / Al-4.5 Cu Lim et al. (1999), Mandal et al. (2004), Daset al. (2007) and Rohatgi et al. (2010)

Al-2Mg Mandal et al. (2007)

A359 /Al-Si10Mg Daoud and Abou El-khair (2010), Huber et al.(2006)

A356 /Al-Si10 Bai et al. (1992), Ravikiran and Surappa(1997), Nagarajan et al. (1999), Chen et al.(2000), Riahi and Alpas (2001), Acilar andGul (2004), Akhlaghi et al. (2004), Gul andAcilar (2004), Natarajan et al. (2006), Yalcinand Akbulut (2006), Sudarshan and Surappa(2008) and Rashed and Mahmoud (2009)

Al-12 Si Cao (2000) and Jun et al. (2004)

Al-12Si-4Mg Anasyida et al. (2010)

Al-12Si-3Cu Basavakumar et al. (2009)

Al-22Si Moustafa (1995)

Al-20Si-3Cu-1Mg Bai and Xue (1997)

Al-13Si-1Mg-1Cu Liu et al. (1997)

Al-Si12Fe Singh et al. (2001)

Al-Si12Cu Akbulut et al. (1998) and Sawla and Das(2004)

Al-4Cu-1.5Mg Nath et al. (1980)

Al–Mg–Si Corrochano et al. (2011)

Al-ZnMg Rao et al. (2010)

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Various particulate reinforcements were added mainly to improve

the wear resistance of aluminium alloys. Hybrid composites containing

addition of more than one particulate have also been investigated. A summary

of various reinforcements added is listed in Table 2.3.

Table 2.3 Particulate Reinforcements used in aluminium MMCs

Reinforcement Reference

Al2O3 Surappa and Rohatgi (1981), Yang (2003), Al-Qutubet al. (2006), De Portu et al. (2007), Rosenberger et al.(2009), Dharmalingam et al. (2010) and Radhika et al.(2011)

SiC Alpas and Zhang (1992), Pai et al. (1995), Zhang et al.(1996), Chen et al. (1997), Tjong et al. (1998), Lim et al.(1999), Haque and Sharif (2001), Srivatsan and Al-Hajri(2002), Shorowordi et al. (2003) , Gomez de Salazar andBarrena (2004), Mart et al. (2005), Yalcin and Akbulut(2006), Rodriguez et al. (2007), Sahin and Özdin (2008),Rashed and Mahmoud (2009), Kumar and Balasubramanian(2010), Rao and Das (2011), Wang and Song (2011) andManigandan et al. (2012)

B4C Ipek (2005), Shorowordi et al. (2006) and Soy et al. (2011)

TiC Sheibani et al. (2007)

SiO2 Pai et al. (1995) and Rohatgi et al. (2010)

Fly ash Sudarshan and Surappa (2008), Tripathy (2009) and VenkatPrasat et al. (2011)

Granite Singh et al. (2001)

TiO2 Pai et al. (1995) and Ramesh et al. (2009)

TiB2 Mandal et al. (2007), Kumar et al. (2008), Natarajan et al.(2009) and Mallikarjuna et al. (2011)

Graphite Pai and Rohatgi (1978), Biswas et al. (1980), Lin et al.(1998), Suresha and Sridhara (2011) and Menezes et al.(2012)

14

2.2 MECHANICAL PROPERTIES OF AMCS

The addition of particulates affects the various mechanical

properties of the composites like tensile strength and hardness. Composites

have enhanced mechanical behaviour when compared to the base alloy.

Doel and Bowen (1996) have studied the effect of SiC particles on

composite tensile behaviour and concluded that all the composites exhibited

lower ductility than the unreinforced material, with the composites containing

fine SiCp (5 m) being relatively more ductile and those reinforced with

coarse SiCp (60 m) exhibited very low ductility. Composites reinforced with

5 and 13 m particles respectively showed greater 0.2% proof stress and

tensile strength values than unreinforced material. However, the composite

reinforced with 60 m particles had lower 0.2% proof stress and tensile

strength values compared to unreinforced alloy.

Sahin and Murphy (1996) observed that the hardness of the Al-

Boron fiber MMCs and the matrix alloy increased linearly and their densities

decreased linearly with volume percent of boron fibre (0-32 vol.%). The

average wear rate of a 32 vol.% fibre composite in normal orientation was

reduced by about 84% compared to the matrix alloy.

Lin et al. (1998) observed a reduction in tensile properties of 6061

aluminum alloy/0–6 wt. % graphite particulate composite. However, the

hardness remained practically unchanged.

Achieving uniform distribution of reinforcement is a foremostrequirement for successful performance of AMCs. Hashim et al. (2002)conducted a systematic study on particle distribution in cast AMCs by usingFinite Element Analysis with a specialized Computational Fluid Dynamicssoftware. Optimum stirring conditions were obtained to achieve effective

15

flow patterns for uniformly dispersing the solid particles in the melt withoutbreaking the surface layer of the melt. In addition, studies on particledispersion behaviour by Seo and Kang (1995) showed that the size and typeof reinforcement had a significant role in determining the mechanicalproperties of the AMCs.

Miyajima and Iwai (2003) investigated the effect of SiC whisker,Al2O3 fiber and SiCp on the mechanical properties of AMCs produced bypowder metallurgy route. Powder metallurgy route was also used by Ling(1995) to evaluate mechanical properties and porosity in AMCs reinforcedwith SiC. It was found that there existed a strong dependence on the kind ofreinforcement and its volume fraction. The results also revealed thatparticulate reinforcement was most beneficial for improving the mechanicalproperties of AMCs. Further Karnezis et al. (1998) reported that, achievinguniform distribution of reinforcement within the matrix was a major challengein the case of Al/SiC composites which directly affects the properties andquality of composite material.

Singla et al. (2009) developed aluminium alloy/ SiCp compositesusing a two step-mixing method of stir casting technique, to fabricatecomposites of varying weight fraction of SiC (5-30%). Results showed thathardness and impact strength increased with an increase in weight percentageof SiC.

Yu et al. (2004) examined a novel method to fabricate uniformlydistributed Al2O3 particles in Al-based metal matrix composite. Thecomposite was formed by sintering an Al-10 wt% ZnO sample at 1000°C.Al2O3 particles were found to be distributed more uniformly in the Al (Zn)solid solution matrix in oil-quenched sample compared to furnace cooledsample. Dobrzañski et al. (2008) have reported the use of sintered Al2O3

particles were used as reinforcements in Al-Si12 alloy to investigate themicrostructure and corrosion resistance of the composites.

16

Xiao-dong et al. (2007) made a study on mechanical properties by

varying the particle size of SiC reinforcement in Al matrix composite

fabricated by squeeze casting technique. They investigated the bending

strength and fracture toughness of the composites and found that as the

particle size decreased, bending strength increased and fracture toughness

decreased. Mechanical properties like bending strength and hardness were

analysed by Altinkok and Koker (2004) in the case of Al2O3/SiC/A332

composites. It was observed that the bending strength and hardness of the

composites increased with decreasing SiCp size.

Das (2004) discussed the development of aluminium alloy

composites for engineering applications. Prototype components of Al-SiC

composites such as brake drums, cylinder block for automobile as well as

parts for mineral processing industries were produced and their performance

under actual operating conditions was evaluated. It was demonstrated that the

composite components have the potential to replace the existing components

made of conventional materials. Enhanced mechanical properties of

composites make them a potential candidate for several engineering

applications

2.3 DRY SLIDING WEAR BEHAVIOUR OF PAMC

According to Sannino and Rack (1995), the important tribological

parameters that control the wear rate and coefficient of friction of

discontinuously reinforced aluminium composites under dry sliding

conditions were the reinforcement type, size, shape, orientation and

reinforcement percentage referred to as the material factors. Applied load,

sliding velocity, sliding distance, environment and temperature as well as

counterfeit material, collectively called as mechanical and physical factors,

also play an important role in controlling the tribological behaviour of

aluminium composites.

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Wear test methods can be grouped into six categories: i) Machinery

Field Tests. ii) Machinery Bench Tests. iii) Systems Bench Tests

iv) Components Bench Tests v) Model Tests vi) Laboratory Tests (Czichos

1992). ASTM committee G-2 on friction and wear test methods address many

of the most common occurrences of friction and wear in machinery. G99-95a

standard describes a laboratory procedure for determining the wear of

materials during sliding using a pin-on-disc apparatus (Blau 1999).

Investigation on the effect of reinforcement by Alpas and Zhang

(1992) showed that at low loads, SiCp acted as load-bearing elements at

stresses lower than the particle fracture strength. It was also observed abrasive

action of the steel counterface caused the transfer of iron-rich layers onto the

contact surfaces. Above a critical load determined by the size and volume

fraction of SiCp, carbide particles on the contact surfaces got fractured. A

subsurface delamination process caused by decohesion of SiC-matrix

interfaces was found to control the wear, resulting in wear rates similar to

those in the unreinforced matrix alloy. An abrupt increase in the wear rates

(by a factor of 100) occurred in the unreinforced aluminium-silicon alloy at a

load of 95 N. SiC reinforcement was proved to be effective in suppressing the

transition from mild to severe wear rate regime.

Sannino and Rack (1995) observed that wear resistance increased

with an increase in reinforcement particulate size in Al 2009/SiC composite.

Scanning Electron Microscopy (SEM) studies showed that adhesion-induced

Tribo-fracture and micro cutting, micro-ploughing and wedge formation were

the predominant wear mechanisms at smaller reinforcement sizes (4, 10 and

13 m), while particulate cracking induced subsurface delamination occurred

in the large ceramic particulate (29 m) reinforced composites. This

behaviour attributed to an increase in particulate size and a consequent

increase in the volume loss.

18

Sharma et al. (1997) showed that the wear rate of the ZA-27 alloy

composites as well as the matrix alloy increased with the increase in load

applied, but decreased with the increase in speed. Composite specimens

exhibited abrasive wear at low loads, while at high loads are delamination

wear was predominant. SEM micrographs of the composite specimens tested

at high loads revealed subsurface cracks, which nucleate due to the stresses,

propagate during the course of the wear to join the wear causing delamination

wear. In addition, with an increase in SiC content, the wear resistance and the

hardness of the composites increased monotonically.

Wilson and Alpas (1997) constructed wear transition maps for

A356 Al and A356 Al - 20% SiC abraded against SAE 52100 steel, which

were used to identify load and speed combinations for different wear rates

and wear mechanism regimes. They found that the addition of SiCp to A356

alloy extended the mild wear regime to higher speeds and loads thereby

slowing down the severe wear. SiCp assisted the retention of an oxide transfer

layer on composite sliding surfaces, which prevented metal-metal contact and

kept wear behaviour within the mild wear regime. When severe wear started

in the composite, the formation of iron oxides from the steel counter face acts

as a lubricant and reduce the wear damage. An ultra-mild wear rate regime

was observed at low sliding speeds and loads where SiCp support the load.

Ravikiran and Surappa (1997) observed that with an increase in

sliding speed, the number of SiCp undergoing fracture decreased in A356/SiC

composites. The wear rate of the pin decreased with an increase in speed. At

lower speeds (less than 2 m/s), pin surface experienced severe damage

resulting in a high wear rate. The area fraction of SiCp exposed on the pin

surface increased with increasing speed. At higher speeds, SiCp protrude

above the matrix due to melting of a thin layer of matrix material and bear

almost the entire load. Formation of a stable iron oxide layer takes place at

19

high speeds, which forms a protective layer on both the pin and the disc

surfaces. Thus, the damage experienced by the matrix decreases with

increasing speed.

Kwok and Lim (1999) noted three distinct regimes (demarcated by

sliding speed) of friction and wear behaviour for Al+4.5%Cu+SiC P/M

processed composites. These regimes were : i) low rate of wear in Regime I

(below 3 m/s), ii) a catastrophic failure of the composites occurred readily in

Regime II (3 to 8 m/s) when a certain critical load is exceeded; and

iii) extensive melting of the composites took place in Regime III (when the

sliding speed exceeds 8 m/s). The catastrophic failure observed in Regime II

occurred when a large amount of the specimen material very quickly adhered

to the counter face, making it impossible to continue with the test. The

extensive melting in Regime III has been attributed to the rapid increase in

bulk temperature of the composites and reaching the melting point of the

Al-alloy matrix. The results obtained suggest that a smaller dispersoid particle

size leads to inferior high-speed wear resistance, with the composite

experiencing extensive melting even at a relatively low load is applied. The

coefficient of friction varies with sliding distance and no unique value could

be associated with each sliding condition.

Bindumadhavan and Wah (2001) observed that in A356/SiC

composite with Dual Particle Size (DPS) of SiC (47 and 120 µm) showed

better wear resistance than the composite having only small (47µm) sized

particles. In these composites, larger SiCp help to carry a greater portion of

the applied load, thereby reducing the load both on the smaller SiC particles

as well as on the base metal. These larger SiC particles also help to shield the

smaller SiC particles from the gouging action of the abrasive, thereby aiding

the smaller particles to continue to perform their wear resisting function.

20

Ranganath et al. (2001) observed that the wear resistance of

Al6061/garnet composites were superior to that of unreinforced matrix alloy .

The Wear resistance increased with the unreinforced matrix of garnet

particulates(4-12 %). The average coefficient of friction of the Al 6061

composite was observed to be lower than that of matrix alloy. Formation of a

Mechanically Mixed Layer (MML) was responsible for the decrease in the

wear-rate and friction coefficient of the MMCs.

Yang (2003) modelled the standard wear coefficients in both the

transient wear and steady-state wear behaviour of Al 6061–Al2O3/steel

system. In the case of 10% Al2O3 composite, higher wear, coefficient values

were observed compared to 15% Al2O3 and 20% Al2O3 reinforced

composites. The observed increase in wear coefficient was attributed to the

presence of a lower volume fraction of Al2O3 in its matrix.

Acilar and Gul (2004) investigated 10% and 30% SiCp reinforced

with Al-Si10 composites and found that the wear rate of both the composites

increased with increasing sliding distance and applied load. The damage to

the surface of the composites increased with increasing load since matrix

materials did not have enough resistance and hence the observed volumetric

wear rate of the composites was more.

Ramesh et al. (2005) evaluated the wear coefficients of Al6061–

TiO2 composites by using Archard’s and Yang’s theoretical models. Increase

in volume fraction of TiO2 resulted in higher hardness and lower wear

coefficient of the composites. The wear coefficient of all the Al6061–TiO2

composites decreased at higher loads and larger sliding distances. 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. This contributes to higher wear

losses of both the matrix alloy and the composites.

21

Al-Qutub et al. (2006) observed that the addition of 10 vol. %, of

sub-micron (0.7µm) Al2O3 particles improved the wear resistance of the 6160

aluminium alloy by up to 45% compared to the unreinforced alloy. Increasing

the Al2O3 content improved the wear resistance up to 145%. It was further

observed that the hardness of the composite increased linearly with the

percentage of Al2O3 particles.

Sevik and Kurnaz (2006) concluded that Al-Si12/Al2O3

composites with larger Al2O3 particles (125 m) showed better wear

resistance than the composites containing small particles (44 m). Large

Al2O3 particles were deeply embedded in the matrix and thus it was relatively

hard to pull out the particles from the matrix. While in composites with

smaller particles, the particles were not embedded deeply embedded and got

easily pulled out of the matrix.

Yalcin and Akbulut (2006) observed that both wear rate and

friction coefficient of the A356 alloy decreased with increasing SiCp content

(5-20 vol.%). However, specimens reinforced with 15 and 20 vol.% SiCp

when tested at 5 N applied load showed an increase in the friction coefficient.

It was suggested that this increase was caused by poor interfacial bonding

between the matrix and SiCp. Poor bonding, associated with particle

segregation can cause particle transfer from the matrix to the Tungsten

Carbide ball and disc interface generating high vibration.

Basavarajappa et al. (2007) observed that the wear rate for

Al2219/15SiC composites and Al2219/15SiC/3Gr hybrid composites were

almost unchanged with an increase in sliding speed upto 3 m/s. Beyond 3 m/s,

the wear rate of the unreinforced alloy increased to larger values than those of

the composites and seizure was observed at a sliding speed of 6.1 m/s. At this

speed, delamination wear was observed to occur in the alloy with fragments

from the pin being transferred to the disc as well as to larger fragments.

22

However, the wear rates of the composites almost unchanged with an increase

in sliding speed upto 4.6 m/s after which there was an increase in wear rate.

Rosenberger et al. (2009) studied the wear behaviour of AA1060

reinforced with Al2O3 under different loads. A mild wear mechanism was

observed for loads lower than 80N, while at larger loads the mechanism

change to a severe wear. In the mild wear regime, a Mechanically Mixed

Layer (MML) consisting of iron from the counter face and material from the

composite, was formed which was responsible for the increased wear

resistance of the composite. Two mechanisms were suggested to explain the

increase in the wear resistance caused by the formation of the MML: (i)

hardening by mechanical alloying and strain hardening of MML and (ii) an

increase in thickness of MML. At larger loads, large-scale instabilities

prevented the formation of a protective MML.

Anasyida et al. (2010) studied the dry sliding wear behaviour of

Al–12Si4Mg alloy with cerium addition and reported that increasing cerium

content up to 2 wt% improved both wear resistance and micro hardness of as-

cast alloys. Addition of more than 2 wt% cerium, however, led to a decrease

in micro hardness, resulting in lower wear resistance of the alloys.

Rao and Das (2011) reported in AA2024/SiC, that as the SiC

content increased, the wear rate and interface temperature decreased, but a

reversed trend was observed for coefficient of friction. Furthermore, they

observed that the wear rate increased with increased in load, speed and sliding

distance.

2.4 WEAR OF HYBRID PAMC

When a soft metal like aluminium slides on hard steel without any

external fluid or solid lubrication, aluminium will flow and adhere to the steel

23

surface and creating an interface of low shear strength. Transfer of aluminium

to steel will continue with sliding ( Prasad and Asthana 2004). Wear debris

may form as a result of ploughing on the soft aluminium surface by the

asperities on the hard steel and flaking off of patches from the transfer film

may also occur. The use of aluminium metal matrix composites (MMC)

reinforced with a solid lubricant (graphite, molybdenum disulfide, antimony

tri-sulphide, copper sulphide, calcium fluoride etc.) along with hard ceramic

particles (SiC, Al2O3, boron carbide, etc.) and/or short fibres can help to

reduce friction and wear of the matrix. Development of aluminium MMCs

dispersed with solid lubricants is primarily directed towards overcoming the

principal drawbacks of aluminium as a tribological material. Rohatgi and co-

workers first introduced graphite as a solid lubricant in aluminium by casting

routes, involving mixing the molten alloy with graphite particles to produce a

uniform dispersion of graphite in the matrix. (Pai and Rohatgi 1978 and

Rohatgi and Pai 1979) .

Wu et al. (1997) observed that the friction and wear behaviour of

Ni/MoS2 self-lubricating composites changed with the formation of a surface

lubricating film. The integrity of the lubricating film could be as a criterion

for estimating the self-lubricating characteristic of the composite. When

homogeneous and continuous lubricating film formed on the overall frictional

surface, the mechanical property of the composite did not show enough

deterioration to cause a remarkable decrease in the film's self-lubrication. The

optimum MoS2 concentration of Ni/MoS2 composite was determined as 60%

under the test condition employed.

Chu and Lin (2000) investigated 6061Al reinforced with 10% SiC

and natural graphite or electroless nickel coated graphite (0, 2, 5, 8 and 11

vol.%) made by P/M route. Wear studies showed that the use of the

electroless nickel film of the graphite particles was significantly beneficial in

24

lowering the wear rate of the component, although it did not produce a great

reduction in the wear rate of composite with pure graphite. Similarly, friction

coefficients were relatively lower when electro less nickel coated graphite

was used.

Riahi and Alpas (2001) studied stir cast A356/10 SiC/4 Gr as well

as A356/5Al2O3/3Graphite. They reported a mild wear regime in the loads of

5–420N and sliding speeds of 0.2–3.0 m/s for both composites. In the mild

wear regime, wear of graphitic composites was primarily controlled by the

formation of a tribo-layer as well as an oxidized surface layer on the contact

surfaces for both composites.

Fu et al. (2004) studied the wear properties of Al/Saffil,

Al/Saffil/Al2O3 and Al/Saffil/SiC hybrid metal matrix composites and

concluded that under dry sliding condition, Saffil/SiC/Al showed the best

wear resistance under high temperature as well as high load, while the wear

resistances of Saffil/Al and Saffil/Al2O3/Al were very comparable.

Benal and Shivanand (2007) studied the effects of reinforcement

content and aging durations on wear characteristics of Al (6061) based hybrid

composites and suggested that abrasive wear resistance of Al-based hybrid

composites may be suitably altered by thermal ageing.

Suresha and Sridhara (2010) studied the effect of addition of

graphite particulates on the wear behaviour in Al/SiC/Gr composites and

concluded that increase of speed reduced wear and with increase in load and

sliding distance increases wear.

Radhika et al. (2011) studied the tribological behaviour of

Al/Al2O3/Gr Hybrid Metal Matrix Composites and suggested that

incorporation of graphite as primary reinforcement increases the wear

25

resistance of composites by forming a protective layer between pin and

counter face. Inclusion of Al2O3 as a secondary reinforcement also has a

significant effect in reducing the wear of the composite.

2.5 ABRASIVE WEAR BEHAVIOUR OF PAMC

In this section, literatures relating to abrasive wear of aluminium-

based MMCs are discussed.

Low stress abrasion studies (three body) generally employ the use

of a Rubber Wheel Abrasion Test (RWAT) conducted as per ASTM-G65

standard (Deuis et al. 1998, Modi et al. 2001 and Murato and Aksoy 2006 ).

High stress abrasion studies (two body) involve a specimen pin sliding under

an applied normal load against a fixed abrasive medium on pin-on-disc

apparatus ( Deuis et al. 1996). Abrasive wear test using a pin-on-disc type

apparatus have been reported by Das et al. (2007), Kok and ozdin (2007) ,

Murato lu and Aksoy (2006) and Sharma et al. (2005). Some of the research

work reported involved the use of a reciprocating type abrasive wear tester

(Singh et al. 2002, Sawla and Das (2004) and Mondal and Das (2006)). Such

tests have been conducted by varying the materials as well as operational

parameters.

Singh et al. (2002) observed that abrasive wear rate of the

composite and the matrix alloy increased with increase in applied load and

abrasive size in Al-Si12Fe/SiC composites. The wear resistance of the

composite was superior to that of the matrix alloy for finer size abrasives,

whereas the trend reversed for coarse sized abrasives. Wear rate also

decreased with increase in sliding distance for composites due to work

hardening of wear surface, clogging, attrition and shelling of abrasive

particles.

26

According to Das et al. (2007) abrasive wear resistance properties

of Al–4.5 wt% Cu alloy was improved significantly by the addition of Al2O3

and ZrO2 particles. A decrease in particle size improved wear resistance for

both Al2O3 and ZrO2 reinforced composites, since smaller particle reinforced

composite has higher hardness and is more efficient in blunting the abrading

surface. ZrO2 reinforced composite shows better wear resistance than Al2O3

reinforced composite due to its superior particle–matrix bonding and due to

increase in hardness.

Das et al. (2008) observed that the abrasive wear rate of

Al-Si12Cu/SiC composite was lower than that of the alloy and decreased with

increasing in SiC content. Further, the wear rate of the composite increased

with increasing size of reinforcement. The alloy exhibited higher wear rate

than that of composites in either cast or heat-treated conditions, irrespective

of applied load and abrasive size. The effect of abrasive size was found to be

insignificant when the abrasive size was less than 60 m. The addition of SiCp

coupled with heat treatment provided significant improvement in wear

resistance.

zciler and Muratoglu (2003) concluded that the abrasive wear rates

of the Al2124/SiC composites increased with an increase in applied load. The

wear rate of the composites tested with SiC abrasive particles showed higher

values than those of the composites abraded by Al2O3 abrasive particles.

Al2O3 abrasive particles showed relatively lower abrasion on the surface of

composites than the SiC abrasive particles due to their relatively higher

hardness.

Kök and Özdin (2007) observed that Al2O3 reinforcement

significantly improved the abrasion wear resistance in Al 2024/Al2O3

composites tested against different abrasives. The wear resistance of the

composites was much higher than that of the unreinforced aluminium alloy.

27

Wear volume loss of the matrix alloy and the composites almost increased

linearly with increasing sliding distance. The wear resistance of the

composites increased with both increase in the Al2O3 particle content as well

as particle size.

Modi (2001) reported that Al 2104/Al2O3 composites experienced

lower material loss than the matrix alloy for all the test conditions employed.

This lower material loss was attributed to the work hardening of the matrix as

well as the protrusion of the dispersoid phase. An increase in the extent of

protrusion of the dispersoid phase with sliding distance offered a higher

degree of protection to the matrix. The composites exhibited maximum wear

loss with SiC abrasive medium while, minimum in the case of ZrO2 and

intermediate in the case of SiO2 reinforcements.

Murato lu and Aksoy (2006) investigated the abrasive wear

behaviour of both as cast and aged Al 2124/SiC composites in the

temperature range 20–200ºC. Wear test results showed that the weight loss of

the aged specimens was lower than that of as cast specimens. It was also

observed that wear resistance improved for specimens tested at room

temperature for both aged and non-aged specimens. Very little change in wear

rate was observed above 50ºC for both aged and as cast specimens. Contact

between SiCp in the composite material and abrasive paper, resulted in broken

or loosened hard SiC abrasives, which penetrated into the soft layer under the

worn surface at temperature between 50–200ºC. This caused an increase in

strength of the surface of the composite specimens and hence resulted in little

change in wear rate.

Sawla and Das (2004) observed superior abrasive wear resistance

in case of Al-Si12Cu/SiC heat-treated composite over as cast composite. It

was also noticed that the wear surface and subsurface deformation of heat-

treated composite showed less damage, reduced degree of crack propagation

28

and lower depth of deformation compared to as cast composite. This was

attributed to the combined effect of the reinforcement of SiC and heat

treatment, which resulted in enhanced hardness and wear resistance of

composite.

2.6 DESIGN OF EXPERIMENT AND OPTIMISATION FOR

TRIBOLOGICAL BEHAVIOUR OF COMPOSITES

DoE is an important and powerful statistical technique to

simultaneously study the effect of multiple variables (Taguchi and Konishi

1987). DoE using Taguchi technique can economically satisfy the needs of

problem solving as well as product/process design optimization by reducing

the variation in a process through robust design of experiments Basso et al.

(2007).

Based on the available literature on the research work carried out

on dry sliding wear and abrasive wear analysis of composites, wear behaviour

can be classified under three categories: (i) experimental investigations

(ii) wear model development and (iii) numerical simulations. Literature

review shows that most literature focus on the first category while the second

and third categories have received much less attention, probably due to the

increased complexity in developing wear models and/or numerical

simulations. Statistical methods have commonly been used for analysis,

prediction and/or optimization of a number of engineering processes. Such

methods enable the user to define and study the effect of every single

condition possible in an experiment where numerous factors are involved. A

review of the statistical methods that have been used for studying the

tribological behaviour of composites is presented in this section.

29

Davim (2000) studied the tribological behaviour of the brass/steel

pair using Taguchi method. Results showed that temperature as well as the

velocity/load and load/temperature interactions had a great influence on the

coefficient of friction. Wear was highly influenced by the load factor and only

a smaller extent by temperature.

Mondal et al. (1998) developed a factorial design of experiment to

describe the high stress abrasive wear behaviour of Al-Si10Cu2Fe/10% Al2O3

composites and derived empirical linear regression equations for predicting

wear rate within a selected domain of experimental wear rates. These

equations qualitatively hold good for matrix alloys and composites and

explain relative influences of individual variables such as load and abrasive

size of the wear resistance of these materials. The effect of load and abrasive

size on the wear rate was relatively more in case of composite material in

comparison to unreinforced alloy.

Basavarajappa and Chandramohan (2006) proposed a Taguchi

Design of Experiments to describe the dry sliding wear behaviour of

Al 2219/15SiC and Al/15SiC/3Gr hybrid composites. Empirical linear

regression equations were developed for predicting the wear volume loss for a

given set of experimental conditions. These equations illustrated that the

Al/SiC/Gr composite exhibited higher wear resistance compared to SiC-

reinforced composites. Wear volume loss decreased with an increase in the

sliding speed for both of the composites, but increased with an increase in

applied load and sliding distance. The interaction effect between load and

sliding speed was predominant in Al/SiC/Gr reinforced composites with

reference to sliding distance.

Sahin and Özdin (2008) employed a factorial Design of an

Experiment to develop linear equations for predicting wear rate of Al/SiC

composites. These equations demonstrated that 10 and 15 wt.% SiC

30

composites exhibited higher wear resistance than that of the unreinforced Al-

2011 matrix alloy. Wear rate of the matrix and composites increased with

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

Among the various parameters, abrasive size was found to be more significant

for composite, followed by load. For the matrix alloy, however, the applied

load was dominant, followed by the abrasive size. The interaction effect of

load and abrasive size was found to be more significant for both alloy matrix

and its composite.

Kök (2010) used Taguchi method to investigate the abrasive wear

behaviour of Al2O3 particle reinforced 2024 aluminium alloy cast composites

under different testing conditions. The results indicated that reinforcement

size was found to be the most influencing factor on abrasive wear, followed

by abrasive grit size. Wear rate of the composites increased with increasing

abrasive grit size and applied load while it decreased with increasing

reinforcement size and sliding distance.

Kumar and Balasubramanian (2010) developed a mathematical

model to predict the abrasive wear rate of AA7075 aluminium alloy matrix

composites reinforced with SiCp. The model was developed using Response

Surface Methodology (RSM). The effect of the volume percentage of

reinforcement, reinforcement size, applied load, sliding speed and abrasive

size on abrasive wear behaviour was analysed. It was concluded that the size

of abrasive exerted the greatest effect on the abrasive wear behaviour of

composite.

Suresha and Sridhara (2010) investigates the dry sliding wear

behaviour of Al-Si7Mg matrix composites reinforced with graphite and 10%

SiCp. Using a Central Composite Design (CCD), they studied the effect of

percentage of reinforcement, load, sliding speed and sliding distance on stir

cast Al / Gr, Al/SiC composites and Al/SiC/Gr hybrid composites. The result

31

showed that hybrid composites exhibited better wear characteristics. Increase

in speed reduced wear, while increase of either load or sliding distance or

both increased the rate of wear rate of the composites.

Sahoo and Pal (2007) studied the tribological performance of

electroless Ni–P coatings and optimizated the tribological test parameters

based on the Taguchi method coupled with Grey Relational Analysis. A Grey

Relational Grade obtained from the analysis was used as a performance index

to study the behaviour of electroless Ni–P coating with respect to friction and

wear characteristics. Grey Relational Analysis was done to find the optimum

test parameter combination that yielded minimum friction and wear

characteristics.

Bayhan and Onel (2010) employed the Response Surface

Optimization to optimize the reinforcement content and sliding distance for

minimizing the wear rate and weight loss of AlSi7Mg/SiCp composites. They

also suggested that for optimum values of reinforcement content and optimum

values of sliding distance, the wear rate of the composite was minimized. In

the experimental region, the average value of optimum friction distance

minimizing the wear rate was found to be about 595m and the average value

of optimum reinforcement content was 13%.

Muhammed et al. (2009) discussed the use of Taguchi method to

optimize stirring time, stirring speed and volume fraction of reinforcement

particles during casting of Al-Si/Al2O3 composites and found that volume

fraction was a major contributing factor for improving tensile strength and

hardness. A similar approach was used by Basavarajappa et al. (2006) to

optimize the process parameters on dry sliding wear behaviour of Al/SiC/Gr

composites.

32

Sahin (2003) reported the abrasive wear behaviour of SiC

reinforced aluminium against SiC and Al2O3 emery papers on a steel counter

face at a fixed speed. Linear factorial design approach was used and the

results showed that the composite exhibited a low wear rate compared to the

unreinforced matrix material against SiC and Al2O3 emery papers. Abrasive

size was found to have significant influence on wear of both matrix alloy and

its composites.

In recent years, techniques like Artificial Neural Network (ANN)

and Genetic Algorithm (GA) have gained importance. Vijian and

Arunachalam (2007) developed a mathematical model for cast Al-Si7Mg

alloy using multi variable regression analysis. Genetic Algorithm was used to

search for optimal squeeze cast process parameters to obtain better

mechanical properties of the composite. This technique was reported to give

promising results.

Sathyabalan et al. (2009) have discussed the effect of

reinforcement (fly ash and SiC) on abrasive wear loss and hardness in

Al-Si12 alloy composites using Artificial Neural Network . A DoE based on

Central Composite Rotatable Method was used to arrive at the proper

combination of parameters and the number of specimens required.

2.7 SUMMARY OF LITERATURE REVIEW

From the literature review, it is evident that a considerable quantity

of studies has been carried out in the field of PAMCs and its manufacturing

techniques to attain different mechanical and tribological properties. The

properties of PAMCs can be enhanced by choosing the appropriate

combination of particulates, its volume fraction and manufacturing technique.

PAMCs are used for various components in aircraft, spacecraft, satellites and

automobiles. The significant amount of research has been done on PAMCs

33

and mechanical properties, tribological behaviour and machining

characteristics of Al MMCs reinforced with different reinforcements

(SiC, Al2O3, graphite, TiB2, etc.,) have been investigated by various

researchers. Heat treatment has also been employed to enhance the strength of

aluminium based alloys and composites.

However, various alloys of aluminium have been used as matrix

materials and SiC has been used as reinforcements, Al-Si10Mg/SiC

composites have not been studied in detail so far. Furthermore, the PAMCs

based on MoS2 as reinforcement have not been studied extensively so far.

In the present study, an attempt has been made to

fabricate Al-Si10Mg/SiC, Al-Si10Mg/MoS2p composites and the

Al-Si10Mg/SiC/MoS2p hybrid metal matrix composites reinforced with SiC

and MoS2 particles. SiCp develop better the specific stiffness, strength and

hardness, while MoS2p impart self lubrication property.

2.8 OBJECTIVES OF THE RESEARCH WORK

Based on the literature review, the following objectives have been

identified for the present study.

i. Fabrication of Al-Si10Mg/SiC, Al-Si10Mg/MoS2p

composites and the Al-Si10Mg/SiCp/MoS2p hybrid metal

matrix composites and analysing their microstructure.

ii. Evaluation of the mechanical properties such as tensile

strength, density, hardness of Al-Si10Mg/SiCp,

Al-Si10Mg/MoS2p composites and Al-Si10Mg/SiCp/MoS2p

hybrid metal matrix composites and compare with those of

matrix alloy.

34

iii. Investigations on the effect of parameters such as applied

load, sliding speed and weight percentage of particulates on

the wear rate for the alloys under

a. Dry sliding wear conditions

b. Abrasive wear conditions

iv. To establish a correlation between the significant parameters

for dry sliding wear namely applied load, sliding speed and

weight percentage of particulates added and determine the

optimum parameters at which there is minimum wear rate

using Response Surface – Genetic Algorithm method.

v. To establish a correlation between the significant parameters

for abrasive wear namely applied load, sliding speed, grit

size and weight percentage of particulates added and

determine the optimum parameters at which there is

minimum wear rate using Response Surface – Genetic

algorithm method.

vi. Comparison of the wear behaviour of composites with those

of hybrid composites