STATE -OF ART REVIEW ANALYSIS OF PRESENT FLY ASH ...joics.org/gallery/ics-1680 - 1.pdfMandal et al (2004) fabricated aluminium matrix composites using stir casting method. Preheated

STATE -OF – ART – REVIEW ANALYSIS OF PRESENT

FLY ASH REINFORCED METAL MATRIX COMPOSITE

Vairavel .M1, R.Girimurugan2, C.Thiruvasagam3 , Selvaraj .M4, S.Saravanan5

1Research And Development Head , Teja Tech Automation Pvt Ltd , Erode ,Tamilnadu

India.

2Assistant Professor ,Department of Mechanical Engineering, Nandha College of

Technology, Perundurai, TamilNadu, India.

3,4Assistant Professor , Department Of Mechanical Engineering , Gnanamani College Of

Technology ,Namakkal , Tamil Nadu ,India

5Associate Professor , Department Of Mechanical Engineering , Gnanamani College Of

Technology ,Namakkal , Tamil Nadu ,India

[email protected]

Abstract

This Papers , Aluminium Matrix Composites are used as materials in automotive

industries owing to their superior strength-to -weight ratio and stiffness.Aluminium

reinforced with conventional ceramic materials such as SiC / Al2O3 are gradually being

implemented in the production of components in automobile industry. Fly ash (SiO2, Al2O3,

Fe2O3 as major constituents and oxides of Gr, Ca, Na, K etc. as minor constituents) is

one of the most inexpensive and low density material which is abundantly available as solid

waste byproduct during combustion of coal in thermal power plants.

Keywords: Review investigation , Metal matrix systems , Components , Analysis ,

Techniques ,

1. Introduction

In liquid phase processing, ceramic particulates are incorporated

into a molten metallic matrix using various proprietary techniques. This is

followed by mixing and eventual casting of the resulting composite mixture into

shaped components or billets for further fabrication. Two phase processes involve

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the mixing of ceramic and matrix and heating in a region of the phase diagram

where the matrix contains both solid and liquid phases. Osprey deposition, compo

casting and variable co deposition of multi-phase materials fall under two phase

composite processes (Rosso 2006).

The liquid phase fabrication methods can be classified in to various types

such as squeeze casting, liquid metal infiltration and spray co deposition

(Sharma 2000).

Solid phase processes involve the fabrication of particulate

reinforced MMCs from blended mixture of elemental powders and

particulates. Powder Metallurgy, High Energy High Rate forming (HERF) and

diffusion bonding fall in this category (Das 2004).

Deposition techniques for MMCs fabrication involve coating individual

fibers in a tow with the matrix material needed to form the composite,

followed by diffusion bonding to form a consolidated composite plate or structural

shape. Important deposition techniques are immersion plating, electro plating,

spray deposition and spray forming techniques.

In situ processing is also called reactive processing. In this process

refractory reinforcements are formed insitu with the alloy matrix by reaction

between the constituents (Surappa 2003).

The present investigation has focused on the utilization of Fly ash in

useful manner by dispersing it into aluminium to produce composites by a

modified two step stir casting method to overcome the cost barrier for wide spread

applications in automotive systems.

In this study, Fly ash particles which are extracted from residues



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generated in the combustion of coal were chosen as reinforcement material. India

produces about 110 million tons of Fly ash per year from burning about 250

million tons of coal for electric power generation.

Aluminium Matrix Composites (AMCs) are used as materials in

aerospace and automotive industries owing to their superior strength- to -

weight ratio and high stiffness. Several research works have been carried out for

the production of composites. They have applied various methods to fabricate

the composites.

Among various processing techniques, stir casting appears to be most

promising route for production of aluminium matrix composites because of

simplicity and capability to produce composites on industrial scale.

Stir casting method is favoured for the production of large number of

complex shaped components in cost effective manner when compared to powder

metallurgy process which has its own limitation such as processing cost and size

limitation on the components.

A major difficulty in stir casting is in obtaining sufficient wetting of

reinforcement particle with the liquid metal in order to get a homogeneous

dispersion and is influenced by

a) Wettability between the matrix and the reinforcement

particles.

b) Porosity in the cast metal matrix composites.

c) Chemical reactions between the reinforcement material and the

matrix alloy.

Achieving a uniform distribution of reinforcement within the matrix is

yet another challenge in the stir casting process, which directly affects on the



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properties and quality of composites.

Interfacial strength between the matrix and reinforcement plays a

significant role in determining the properties of MMCs. These aspects have been

discussed by many researchers. Fly ash particles incorporated into molten Al

were observed to be floating on the molten Al surface due to the high surface

tension which leads poor wettability.

Wettability can be defined as the ability of a liquid to spread on a solid

surface, and represents the extent of intimate contact between a liquid and a solid.

Gas layers at the surfaces of the particles can cause the buoyant migration,

mechanical stirring can be done in a semi solid state rather than in the completely

liquid state to breakdown the gas layers, thereby reducing

surface tension. Wettability can be improved by increasing the surface energies

of the solids, decreasing the surface tension of the liquid matrix alloy and decreasing

the solid/liquid interfacial energy at the reinforcement matrix interface.

Addition of reactive elements such as Li, Gr, Ca, Ti, Zr and P

increases the wettability of metal-ceramic systems by inducing a chemical

reaction at the interface and also by decreasing the surface tension of the

molten Al and the solid-liquid interfacial energy of the melt.

Addition of elements having high affinity for oxygen increases the

wettability of certain ceramic particles. Magnesium, which acts as a powerful

surfactant as well as a reactive element, in the aluminium alloy matrix seems to

fulfill all the above requirements. Important role played by the magnesium during the

composite synthesis is the scavenging of the oxygen from the dispersoid surface,

thus thinning the gas layer and improving wetting action with the surface of the

dispersoids. Conclusions from previous research studies have confirmed the

strengthening of aluminium alloys with a dispersion of particulates, thereby

strongly enhancing their potential in tribological and structural applications.



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In order to achieve the optimum properties of the metal matrix

composite, several factors that have to be considered, including achieving a uniform

distribution of the reinforcement material in molten matrix, improving the

wettability or bonding between the matrix and reinforcement, enhancing the solid

solution strengthening mechanism by interfacial chemical reactions as well as

minimizing the porosity. This requires the sound theoretical and practical

knowledge on the part of composite material engineers.

Mandal et al (2004) fabricated aluminium matrix composites using stir

casting method. Preheated reinforcements at 475K were added to the center of

the vortex formed during stirring.

Chaudhury et al (2004) produced Al-2Gr-11 TiO2 (rutile)

composite using vortex method. The melt was stirred with a stirrer at a

rotational speed of 200rpm. It was observed that, the addition of rutile

particles tend to increase the hardness of composites.

Ipek (2005) fabricated SiC reinforced 4147 Al matrix composites using

liquid metallurgy route. Melt was heated up to 910K and stirring was carried out

approximately 400 rpm speed for 30min under CO2 gas atmosphere to

avoid oxidation.

Sarkar et al (2008) have employed Piston mixing technique to

fabricate Al– Fly ash composites and concluded that up to 17 wt. % Fly ash

could be incorporated in the matrix by liquid metallurgy route. Addition of

magnesium increased the wettability which enhanced the wear resistance and

mechanical properties.

Although a larger number of investigations have been carried out on

mixing in solid– liquid suspensions by applying chemical engineering

principles, the number of studies reported on mixing phenomena in

metallurgical systems is relatively few.



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Rohatgi et al (1998) have conducted a study on the mixing quality of

two phase slurries using SiC– water system to determine the influence of Piston

geometry and baffles on the uniformity of distribution of SiC in the mixture. It was

found that variation of SiC concentration during stirring in the

absence of baffles was 7.5 vol % compared to 2 vol% in the presence of four

baffles.

In order to achieve a good homogeneous distribution of Fly ash

particles in Al matrix, the Piston must be designed such that it creates vortex

in the composite slurry. Hence, a proper understanding of the Piston parameters is

essential.

Inherent difficulties associated with stir casting method are non-

wettability of the reinforcement particles by liquid Al, segregation of

particles, higher porosity and extensive interfacial reaction due to higher processing

temperature. Porosity in stir castings occurs as a result of gases entrapped during

melting as well as during stirring/mixing, which form gas bubbles, leading to large

scale porosity (Hashim et al 1999, 2003).

The amount of porosity depends on the processing parameters, type of

matrix and reinforcement, weight fraction of reinforcement and interfacial reaction.

The distribution of the reinforcement particles in the molten matrix ledepends 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 (Girot et al 1987). Non-uniform distribution of reinforcements could

lead slip of dislocations and initiation of micro cracks which causes premature

failures in the composite

As the reinforcement content in the melt increases, the inter particle

distance is lowered and clusters formation occurs which leads to the

entrapment of gas layers between the particles. These layers drag the reinforcement



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particles together leading to spontaneous rejection from the Al melt. In order to

distribute the lumps into small aggregates, it is important to increase the shear force

in the composite slurry.

In the present study a modified two stage stir casting technique has been

implemented to produce the Al- Fly ash particulate composites with an objective to

obtain homogenous dispersion of Fly ash material in the pure commercial Al.

2. WEAR BEHAVIOUR OF MATERIALS

2.1 Introduction

Wear is material removal from one surface of the component to

another during relative motion between them. Adhesive wear occurs when two

solid surfaces slide over one another under pressure whereas abrasive wear may

involve gouging, grooving, as well as plastic deformation caused by the penetration

of hard abrasive reinforcement particles (Prasad et al 1986). Materials with a high

hardness, strength and toughness are most resistant to abrasive wear (Askeland and

Phule 2002).

Presence of a particulate reinforcement in metal matrix enhances the

tribological characteristics along with higher specific strength and stiffness making

them good candidate materials for many engineering situations where sliding contact

is expected (Ibrahim et al 1991, Sinclair and Gregson 1997). Several investigations

have been carried out experiments for analyzing the wear behaviour of

aluminium matrix composites.

The most commonly employed metal matrix composite system consists of aluminium alloy

reinforced with hard ceramic particles such as SiC, Al2O3, (Ma et al 2003, Muratoglu

and Aksoy 2000) or soft particles such as Graphite and Talc (Zhang et al 1994). Recently

low-cost and low-density Fly ash particulate reinforcements are being investigated as

replacements for the relatively more expensive conventional reinforcements such as

SiC,B4C and Al2O3.



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2.2 Wear Behaviour of Composites

Various researchers have carried out experiments for evaluating the wear

behaviour of aluminium matrix composites.

Ramachandra and Radhakrishna (2007) have investigated the effect of

Fly ash content on sliding wear, slurry erosive wear and corrosive behaviour

of aluminium matrix composites produced by stir casting method and concluded

that Al (12 wt% Si) -15 wt% of Fly ash particulate composite showed improved

abrasive wear resistance. Increase in normal load and sliding velocity increased

the magnitude of wear and frictional force.

Addition of 6% of Fly ash particles into A356 Al alloy showed

lower wear rates at low loads (10 and 20 N) while 12% of Fly ash reinforced

composites showed lower wear rates compared to the unreinforced alloy in the

load range 20–80 N. At higher load, subsurface delamination is the main mechanism

in both the Al alloy as well as in composites (Sudarshan and Surappa 2008).

Gurcan and Baker (1995) investigated the wear resistance of Al

6061 reinforced with SiC composites. The maximum wear resistance was

observed in the composite containing 20 wt. % of SiC particles.

Seah et al (1996) reported an increase in the wear resistance of cast

ZA-27- Gr composites with the increase in graphite reinforcement up to

1 wt. %. Further addition of graphite results only in marginal improvement in the

wear resistance. It also lowers the hardness of the material.

Zhan and Zhang (2006) reported that inclusion of graphite with

copper - SiCp composite retards severe wear at higher temperatures and delays

the start of seizure due to the prevention of metal-to-metal contact.



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Tedguo and Tsao (2000) studied the wear behaviour of self

lubricating Al hybrid composites reinforced with SiC and graphite particles. They

reported that as the incorporation of graphite particles decreased friction coefficient

and wear rate considerably.

Suresha et al (2010) investigated the influence of reinforcement content,

sliding load, sliding speed and sliding distance on wear behaviour of Al–Gr, Al–SiC

composites and Al–SiC–Gr hybrid composites. Parametric studies revealed that

hybrid composites exhibit better wear characteristics.

Vencl et al (2010) studied the tribological behaviour of heat treated Al356

composites reinforced with Al2O3 / SiC and graphite particles fabricated by

compo casting process.The results revealed that the wear resistance and

coefficient of friction were better at the SiC particulate composites compared to

Al2O3 particulate composite, while the incorporation of graphite particles enhanced

the wear resistance further.

Mondal et al (1998) studied abrasive wear behaviour of Al alloy– Al2O3

composites as a function of applied load, size and volume fraction of

reinforcement. It was observed that the wear rate of composite decreases

linearly with increase in Al2O3 content and the wear resistance of composite varied

inversely with square of the reinforcement size.

3.CONCLUSIONS

The major review conclusions drawn from the present study on

investigations on mechanical, dry sliding wear behavior and mechanical

characteristics of metal matrix composites are summarized.



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STATE -OF ART REVIEW ANALYSIS OF PRESENT FLY ASH ...joics.org/gallery/ics-1680 - 1.pdfMandal et al (2004) fabricated aluminium matrix composites using stir casting method. Preheated