FABRICATION AND ANALYSIS OF ALUMINIUM METAL

MATRIX COMPOSITE

PROJECT REPORT

PHASE I

Submitted to the

FACULTY OF MECHANICAL ENGINEERING

In partial fulfillment for the award of the degree

Of

MASTER OF ENGINEERING

IN

COMPUTER AIDED DESIGN

By

MARLON JONES LOUIS

Reg No: 081007801005

DEPARTMENT OF MECHANICAL ENGINEERING

GOVERNMENT COLLEGE OF ENGINEERING, SALEM- 636 011

ANNA UNIVERSITY: COIMBATORE

NOVEMBER 2009

GOVERNMENT COLLEGE OF ENGINEERING

SALEM-11

DEPARTMENT OF MECHANICAL ENGINEERING

BONAFIDE CERTIFICATE

Certified that this Phase-I project titled, FABRICATION AND ANALYSIS OF

ALUMINIUM METAL MATRIX COMPOSITE is the bonafide work of

MARLON JONES LOUIS, Register Number: 081007801005 who carried out the

research under my supervision. Certified further, that to the best of my knowledge the work

reported here is does not form part of any thesis or dissertation on the basis of which, a

degree or award was conferred on an early occasion on this or any other candidate.

Head of the Department Project Guide

Prof.P.K. JAYADEV, M.E., Dr.R.MALAYALAMURTHY, M.E., PhD (Assistant Professor)

Dept. of mechanical engineering Dept. of mechanical engineeringGovernment College of engineering Government College of engineeringSalem – 11 Salem – 11

Submitted for the Project Viva-Voce examination held on………….

Internal Examiner External Examiner

ACKNOWLEDGEMENT

I wish to express my sincere gratitude to Dr.S.R.DAMODHARASAMY, The

Principal, Government college of Engineering, Salem-11, for providing me a golden

opportunity to do this project.

I wish to record my immense appreciation and sincere thanks to my guide,

Asst.Prof.Dr.R.MALAYALAMURTHY Department of Mechanical Engineering, for

selecting this project and his hortatory and valuable guidance, encouragement and

constructive criticisms at all stages of this project

I sincerely thank Prof.P.K.JAYADEV, Professor and Head, Department of

Mechanical Engineering for this guidance, constant supervision, suggestion and showing

immense important to my project work.

I wish to thank my class advisor, Mr.A.BARANIRAJ, Lecturer, Department of

Mechanical Engineering, for intellectual support, encouragement, and enthusiasm which

made this project possible.

I wish to take this opportunity to thank staff members of faculty of Mechanical

Engineering for their valuable suggestions and support Finally, I thank one and all those

who are rendering help directly and indirectly at various stages of this project.

ABSTRACT

In the field of material science and engineering, there is a great impact ever

since the invention of composites materials. High strength and lightweight remain

the winning combination that propels composite materials into new arenas. The

composite materials replace conventional materials like steel, cast iron and

aluminum alloys by its superficial properties. As literatures were collected, it could

be found that metal matrix composites are under serious consideration as potential

candidate materials. To replace conventional materials in aerospace and automotive

applications. In this project, composites based on aluminum alloy (Al 2024)

reinforced with 10% volume fraction of Silicon Carbide Particulates (SiC) and 5 %

volume fraction of Graphite particles is produced by stir casting method. The

fabricated composite is tested in order to find its properties and the specimen is

analyzed using Ansys software version 10.0. in order to study on cracks

TABLE OF CONTENTS

CHAPTER TITLE PAGE NO

1. INTRODUCTION

1.1 OBJECTIVE

2. LITERATURE REVIEW

3. COMPOSITE MATERIALS

3.1 COMPOSITE MATERIALS

3.2 CLASSIFICATION OF COMPOSITES

3.2.1 Based on matrix

3.2.1.1 Polymer matrix composites

3.2.1.2 Ceramic matrix composites

3.2.1.3 Metal matrix composites

3.2.2 Based on material structure

3.2.2.1 Particulate composites

3.2.2.2 Fibrous composites

3.2.2.3 Laminate composites

3.3APPLICATION OF COMPOSITES

4. METAL MATRIX COMPOSITES

4.1CLASSIFICATION OF METAL MATRIX COMPOSITES

4.1.1 Particle reinforced composites

4.1.2 Whisker-reinforced composites

4.1.3 Continuous fiber-reinforced composites

4.2 PROCESSING OF METAL MATRIX COMPOSITES

4.2.1 Solid state processing

4.2.1.1 Diffusion bonding

4.2.1.2 Sintering

4.2.2 Liquid state processing

4.2.2.1 Stir casting

4.2.2.2 Infiltration

4.2.3 In-situ fabrication

5. CRACKS

6. FABRICATION OF COMPOSITE

6.1 SELECTIONS OF MATERIALS AND COMPOSITION

6.1.1 Matrix material

6.1.2 Reinforcement materials

6.2 FABRICATION METHOD

7. CONCLUSION

8. APPENDICES

9. REFERNCES

LIST OF TABLES

TABLE NO. TITLE PAGE NO

6.1 CHEMICAL COMPOSITION OF ALUMINIUM 2024

6.2 TYPICAL COMPOSITION OF ALUMINIUM 2024

LIST OF FIGURES

FIGURE NO. TITLE PAGE NO

3.1. PARTICULATE COMPOSITE

3.2. SHORT FIBRES REINFORCED COMPOSITE

3.3. LONG FIBRES REINFORCED COMPOSITE

5.1. THREE LOADING MODES

NOMENCLATURE

ABBREVATIONS

ANSYS Analysis Software

SiCp Silicon Carbide Particulates

Gr Graphite

Al203 Aluminium oxide

CHAPTER 1

INTRODUCTION

In an advanced society like ours we all depend on composite materials in

some aspect of our lives. Fiber glass, developed in the late 1940s, was the first

modern composite and is still the most common. It makes up about 65 per cent of all

the composites produced today and is used for boat hulls, surfboards, sporting

goods, swimming pool linings, building panels and car bodies. Composites exist in

nature. A piece of wood is a composite, with long fibers of cellulose (a very

complex form of starch) held together by a much weaker substance called lignin.

Cellulose is also found in cotton and linen, but it is the binding power of the lignin

that makes a piece of timber much stronger than a bundle of cotton fibres. In

engineering materials, composites are formed by coatings, internal adhesives and

laminating. An important metal composite is clad metals. Thermostatic controls are

made by roll-bonding a high expansion alloy such as copper to a low expansion

alloy like steel. When the composite is heated it will deflect to open electrical

contacts. Ply wood is a similarly common composite. Since wood is weaker in its

transverse direction than its long direction, the alternating grain in plywood

overcomes the transverse deficiency.

Humans have been using composite materials for thousands of years. The

greatest advantage of composite materials is strength and stiffness combined with

lightness. In Modern aviation, both military and civil would be much less efficient

without composites. In fact, the demands made by that industry for materials that are

both light and strong has been the main force driving the development of

composites. The airframes of some smaller aircraft are made entirely from

composites, as are the wing, tail and body panels of large commercial aircraft.

Composites can be molded into complex shapes. Another advantage of composite

materials is that they provide design flexibility. Over recent decades many new

composites have been developed, some with very valuable properties. There are

varieties of composites that can be manufactured according to the requirements of

desired properties for a particular application.

Composites as a class of engineering materials provide almost unlimited

potential for higher strength, stiffness and corrosion resistance over pure material

systems of metals, ceramics and polymers. This will probably be “the steels” of the

next century.

Composite materials are formed by combining two or more materials that

have quite different properties. The different materials work together to give the

composite unique properties, but within the composite the materials can be

differentiated since they do not dissolve or blend into each other. Composites are

made up of two materials namely matrix and reinforcement. The matrix or binder

surrounds and binds together a cluster of fibres or fragments of the stronger material

(reinforcement).

In Metal Matrix Composites (MMCs), ceramics or metals in form of

fibres, whiskers or particles used to reinforce in a metal matrix. Most commonly

used matrixes are aluminum, magnesium, copper, titanium and zinc. The most

commonly used reinforcements are silicon carbide, alumina, boron, graphite and fly

ash. The strengthening effect of the reinforcements in composites depends on the

orientation of the reinforcements to the direction of the loads.

1.1OBJECTIVE

The objectives of this project are

To fabricate Metal matrix composites with the base metal as Aluminum

reinforced with a Volume of 10 % of Silicon carbide particulates and 5 % of

graphite particulates by Stir casting method.

To study the cracks using Ansys version 10.0 software

CHAPTER 2

LITERATURE REVIEW

The Al metal matrix composites offer wide range of properties suitable

for a large number of engineering applications. Sufficient literatures are available on

different aspects of tribology and machining of conventional metals and alloys but

limited literature are available for reinforced metal matrix composites.

Aluminum-Silicon (Al--Si) casting alloys are the most versatile of all

common foundry cast alloys in the production of pistons for automotive engines.

Depending on the Si concentration in weight percent, the Al--Si alloy systems fall

into three major categories: hypoeutectic (<12 wt % Si), eutectic (12-13 wt % Si)

and hypereutectic (14-25 wt % Si). However, commercial applications for

hypereutectic alloys are relatively limited because they are among the most difficult

Al alloys to cast and machine due to the high Si contents.

When high Si content is alloyed into Al, it adds a large amount of heat

capacity that must be removed from the alloy to solidify it during a casting

operation. Significant variation in the sizes of the primary Si particles can be found

between different regions of the cast article, resulting in a significant variation in the

mechanical properties for the cast article. The primary crystals of Si must be refined

in order to achieve hardness and good wear resistance. On the other hand, the usage

of hypoeutectic and eutectic alloys are very popular for the industry, because they

are more economical to produce by casting, simpler to control the cast parameters,

and easier to machine than hypereutectic. However, most of them are not suitable for

high temperature applications, such as in the automotive field, for the reason that

their mechanical properties, such as tensile strength, are not as high as desired in the

temperature range of 500° F.-700° F. Current state-of-the-art hypoeutectic and

eutectic alloys are intended for applications at temperatures of not higher than about

450° F. The undesirable microstructure and phase transformation results in

drastically reduced mechanical properties, more particularly the ultimate tensile

strength and high cycle fatigue strengths, for hypoeutectic and eutectic Al--Si alloys.

One approach taken by the art is to use ceramic fibres or ceramic

particulates to increase the strength of hypoeutectic and eutectic Al--Si alloys. This

approach is known as the aluminum Metal Matrix Composites (MMC) technology.

For example, R. Bowles has used ceramic fibres to improve tensile strength of a

hypoeutectic 332.0 alloy, in a paper entitled, "Metal Matrix Composites Aid Piston

Manufacture," Manufacturing Engineering, May 1987.

Moreover, A. Shakesheff has used ceramic particulate for reinforcing

another type of hypoeutectic A359 alloy, as described in "Elevated Temperature

Performance of Particulate Reinforced Aluminum Alloys," Materials Science

Forum, Vol. 217-222, pp. 1133-1138 (1996).

In a similar approach, cast aluminum MMC for pistons using eutectic

alloy such as the 413.0 type, has been described by P. Rohatgi in a paper entitled,

"Cast Aluminum Matrix Composites for Automotive Applications," Journal of

Metals, April 1991.

Vikram Singh and R.C. Prasad has fabricated and analyzed the tensile and

fracture behavior of 6061 Al-SiCp metal matrix Composite by reinforcing with 5%,

10% and 15 volume % SiC particles. Vidya Sagar Avadutala has analyzed the cracks

in composite materials (aluminum and low carbon steel) using Ansys.

CHAPTER 3

COMPOSITE MATERIALS

3.1 COMPOSITE MATERIALS

Composite material is a material composed of two or more distinct

phases (matrix phase and dispersed phase) and having bulk properties significantly

different from those of any of the constituents.

Matrix phase is the primary phase having a continuous character. Matrix

is usually more ductile and is a less hard phase. It holds the dispersed phase and

shares a load with it.

The second phase (or phases) is embedded in the matrix in a

discontinuous form. This secondary phase is called dispersed phase. Dispersed phase

is usually stronger than the matrix, therefore it is sometimes called reinforcing

phase.

Many of common materials (metal alloys, doped Ceramics and Polymers

mixed with additives) also have a small amount of dispersed phases in their

structures, however they are not considered as composite materials since their

properties are similar to those of their base constituents.

3.2 CLASSIFICATION OF COMPOSITES

There are two classification systems of composite materials. One of them

is based on the matrix material and the second is based on the material structure.

3.2.1 BASED ON MATRIX

One commonly used classification of composites is based on matrix used

based on the base matrix composites can be divided into three main groups:

I. Polymer Matrix Composites (PMCs)

II. Ceramic Matrix Composites (CMCs)

III. Metal Matrix Composites (MMCs)

3.2.1.1 POLYMER MATRIX COMPOSITES

Polymer Matrix Composite (PMC) is material consisting of polymer

(resin) matrix combined with a fibrous reinforcing dispersed phase. Polymer Matrix

Composites are very popular due to their low cost and simple fabrication methods.

Use of non-reinforced polymers as structure materials is limited by low level of their

mechanical properties. For example the tensile strength of one of the strongest

polymers - epoxy resin is 20000 psi (140 MPa). In addition to relatively low

strength, polymer materials possess low impact resistance. Two types of polymers

are used as matrix materials for fabrication composites. Thermosets (epoxies,

phenolics) and Thermoplastics (Low Density Polyethylene (LDPE), High Density

Polyethylene (HDPE), polypropylene, nylon, acrylics).

According to the reinforcement material, the groups of Polymer Matrix

Composites (PMC) used are Fibreglasses, Carbon Fibres, and Kevlar. Reinforcing

fibres may be arranged in the form of Unidirectional fibres, Ravings, Veil mat,

Chopped strands, Woven fabric.

3.2.1.2 CERAMIC MATRIX COMPOSITES

Ceramic Matrix Composite (CMC) is material consisting of a ceramic

matrix combined with a ceramic (oxides, carbides) dispersed phase. Ceramic Matrix

Composites are designed to improve toughness of conventional ceramics, the main

disadvantage of which is brittleness. Ceramic Matrix Composites are reinforced by

either continuous (long) fibres or discontinuous (short) fibres. These composites are

mainly used for high temperature applications and in electronic industries.

3.2.1.3 METAL MATRIX COMPOSITES

Metal Matrix Composite (MMC) is material consisting of a metallic

matrix combined with a ceramic (oxides, carbides) or metallic (lead, tungsten,

molybdenum) dispersed phase. Most commonly used matrixes are aluminium,

magnesium, copper, titanium and zinc. The most commonly used reinforcements are

silicon carbide, alumina, boron, graphite and fly ash. Development of these materials

is a subject of great interest as they offer attractive combination of physical and

mechanical properties, which cannot be obtained in monolithic alloys.

3.2.2 BASED ON MATERIAL STRUCTURE

Based on the material structure composites are classified into

1. Particulate composites

2. Fibrous composites

3. Laminate composites

3.2.2.1 PARTICULATE COMPOSITES

Particulate Composites consist of a matrix reinforced by a dispersed

phase in form of particles.

Figure 3.1 Particulate Composite

These particles are sometimes divided into two subclasses:

a) Composites with random orientation of particles.

It is a structure filled with one or more additional materials.

b) Composites with preferred orientation of particles.

Dispersed phase of these materials consists of two-dimensional flat platelets

(flakes), laid parallel to each other.

Effect of the dispersed particles on the composite properties depends on

the particles dimensions. Very small particles (less than 0.25 micron in diameter)

finely distributed in the matrix impede movement of dislocations and deformation of

the material. Such strengthening effect is similar to the precipitation hardening. In

contrast to the precipitation hardening, which disappears at elevated temperatures

when the precipitated particles dissolve in the matrix, dispersed phase of particulate

composites (ceramic particles) is usually stable at high temperatures, so the

strengthening effect is retained. Many of composite materials are designed to work

in high temperature applications. Large dispersed phase particles have low

strengthening effect but they are capable to share load applied to the material,

resulting in increase of stiffness and decrease of ductility. Hard particles dispersed in

a softer matrix increase wear and abrasion resistance. Soft dispersed particles in a

harder matrix improve machinability (lead particles in steel or copper matrix) and

reduce coefficient of friction (tin in aluminium matrix or lead in copper matrix).

3.2.2.2 FIBROUS COMPOSITES

They are composed of reinforced fibres in matrix. They are further

classified as Short –fibres and long-fibres reinforced composites.

1. Short-fibres reinforced composites:

Short-fibres reinforced composites consist of a matrix reinforced by a

dispersed phase in form of discontinuous fibres (length < 100*diameter).

Figure 3.2 Short Fibres Reinforced Composite

1. Composites with random orientation of fibres.

2. Composites with preferred orientation of fibres.

2. Long-fibres reinforced composites:

Long-fibres reinforced composites consist of a matrix reinforced by a

dispersed phase in form of continuous fibres.

Figure 3.3 Long Fibres Reinforced Composite

1. Unidirectional orientation of fibres.

2. Bidirectional orientation of fibres (woven).

The length of a fiber affects the properties of the composites and also its

processing characteristics. Generally continuous fibres are easier to handle than

short fibres. The fiber reinforced composites are of interest in aerospace applications

where weight saving is of great importance

3.2.2.3 LAMINATE COMPOSITES

Laminate composites consist of layers with different anisotropic

orientations or of a matrix reinforced with a dispersed phase in form of sheets.

When a fibres reinforced composite consists of several layers with

different fibres orientations, it is called multilayer (angle-ply) composite.

Laminate composites provide increased mechanical strength in two

directions and only in one direction, perpendicular to the preferred orientations of

the fibres or sheet, mechanical properties of the material are low. The best example

of laminar composite is plywood.

3.3 APPLICATION OF COMPOSITES

Hybrid materials and composites form the key to successful development

of next-generation aerospace propulsion and power systems. Metal-matrix

composites play a significant role in the development of future aerospace

components. These materials are not only resistant to high temperatures, but also

provide significant improvements in weight specific mechanical and thermal

properties.

Aluminum is the most attractive non-ferrous matrix material extensively

used particularly in the aerospace industry where weight of structural components is

crucial .The low density and high specific mechanical properties of aluminum metal

matrix composites (MMC) make these alloys one of the most interesting material

alternatives for the manufacture of lightweight parts for many types of vehicles.

With wear resistance and strength equal to cast-iron, 67% lower density and three

times the thermal conductivity, aluminum MMC alloys are ideal materials for the

manufacture of lightweight automotive and other commercial parts. The majority of

effort in aluminum matrix composites has been directed toward development of high

performance composites, with very high strengths and module, for use in specialized

aerospace applications. However, there are a number of other applications in aircraft

engines and aerospace structures where these very high properties may not be

required, and where it could be cost effective to use other metal matrix composites.

For example cost, weight, and stiffness-critical components, such as engine static

structures, do not require the very high directional properties available with

composites reinforced with aligned continuous fibres. For these reasons, efforts were

initiated to assess the potential of applying low cost aluminum matrix composites to

these structures, using low-cost reinforcements and low-cost composite fabrication

processes, including powder metallurgy, direct casting, and hot molding techniques.

Cryogenically processed automobile components like brake rotors, gears,

piston, connecting rods, engines and machine parts, tools and gun barrels show

significant extension in the performance and productive life.  The metallurgy behind

cryogenic processing is that it creates a large amount of fine or small carbides that

precipitate uniformly throughout the lattice structure, closes and refines grain

structures. Treated piston rings seal better against treated cylinder walls reducing

blow-by and increasing horsepower. Cylinder blocks do not distort and cylinder

bores stay straight and smooth when subjected to heat and vibration.

Application of SiC/Al Composites to Aircraft Engine and Aerospace Structures

Studies show that these low cost SiC/Al matrix composites demonstrated

a good potential for application to aerospace structures and aircraft engine

components. The composites are formable with normal aluminum metal-working

techniques and equipment at warm working temperatures. They can also be made

directly into structural shapes during fabrication.

These composites merit additional work to determine fatigue, long-term

stability, and thermal cycle behavior to characterize more fully their properties and

allow their consideration for structural design for a variety of aircraft and spacecraft

applications.

The most significant aspect of these data was the increase in modulus

over that of competitive aluminum alloys. At 20 % vol reinforcement, the modulus

of SiC/Al composites was about 50% above that of aluminum and approached that

of titanium. This increase in modulus was achieved with a material having a density

one-third less than that of titanium. Comparison of the properties of the various

composites shows that the modulus/density ratio of 20 vol % SiC/Al composites was

about 50% greater than that of Al or Ti alloys, while at 30 vol % SiC the advantage

was increased to about 70% and at 40 vol % SiC the modulus was almost double that

of unreinforced Al or Ti structural alloys

CHAPTER 4

METAL MATRIX COMPOSITES

Strength is maximum. Properties of the matrix and the composition of the

Conventional monolithic materials have limitations in terms of achievable

combinations of strength, stiffness, coefficient of expansion and density. MMCs

have emerged as an important class of advanced materials giving engineers the

opportunity to tailor the material properties according to their needs. A Metal matrix

composite is an engineered combination of two or more materials (one of which is a

metal) in which tailored properties are achieved by systematic combination of

different constituents. MMC's desirable properties result from the presence of small,

high strength ceramic particles, whiskers or fibres uniformly distributed throughout

the aluminum alloy matrix. Aluminum MMC castings are economically competitive

with iron and steel castings in many cases. However the presence of these wear

resistant particles significantly reduces the machinability of the alloys, making

machining costs higher due mainly to increased tool wear. As a result, the

application of cast MMCs to components requiring a large amount of secondary

machining has been somewhat stifled.

Development of these materials is a subject of great interest as they offer

attractive combination of physical and mechanical properties, which cannot be

obtained in monolithic alloys. Essentially, these materials differ from the

conventional engineering materials from the point of homogeneity.

The major advantages of MMCs compared to unreinforced materials are as follows:-

Higher strength-to-density ratios

Higher stiffness-to-density ratios

Better fatigue resistance

Better elevated temperature properties

Lower coefficients of thermal expansion

Improved abrasion and wear resistance

Improved damping capabilities

4.1 CLASSIFICATION OF METAL MATRIX COMPOSITES

Classifications of MMCs based on reinforcement are

Particle reinforced composites

Whisker reinforced composites

Continuous fiber-reinforced composites

These classes are briefly discussed in the following sections,

4.1.1 PARTICLE REINFORCED COMPOSITES

Particulate composites consist of one or more materials suspended in a

metal matrix. These composites generally contain ceramic reinforcements with an

aspect ratio less than 5. Ceramic reinforcements used are generally Al2O3, SiCp or

Gr and present normally in volume fraction less than 30 % when used for structural

and wear resistance applications. Mechanical properties of PMMCs are inferior

compared to whisker/fiber reinforced MMCs but far superior compared to

unreinforced alloys. These composites are near isotropic in nature and can be

subjected to forming operations like extrusion, rolling and forging.

4.1.2 WHISKER-REINFORCED COMPOSITES

Whiskers are generally very short and stubby although the length-to-

diameter ratio can vary from 20 to 200. Whisker is more perfect than a fiber and

hence exhibits even better properties. Whiskers are obtained by crystallization on a

very small scale resulting in a nearly perfect alignment of crystals. Short alumina

fiber reinforced aluminium matrix composites is one of the first and most popular

MMCs to be developed and used in automobile pistons. Mechanical properties of

whisker reinforced composites are superior when compared to particle reinforced

composites. Whiskers can be incorporated into the composites by various

techniques like powder metallurgy and casting techniques to produce metal/whisker

systems.

4.1.3 CONTINUOUS FIBER-REINFORCED COMPOSITES

In fibre reinforced composite materials, the fibre orientation decides the

strength of the composite and the direction in which the matrix and the properties of

the fibre are other factors which influence the performance of the fibre-reinforced

composites. Fibre reinforced composites are produced from a wide range of

constituent materials. The length of a fibre affects the properties of the composites

and also it’s processing characteristics. Generally continuous fibres are easier to

handle than short fibres. The fibre reinforced composites are of interest in aerospace

applications where weight saving is of great importance.

4.2 PROCESSING OF METAL MATRIX COMPOSITES

Fabrication methods are important part of the design process for all

structural materials including MMCs. Considerable work is under way in this critical

area. Different manufacturing techniques are used to fabricate the metal matrix

composites. They can be classified into,

Solid state processing

Liquid state processing

In-situ processing

The different processing routes for MMCs are briefly discussed in the following

sections.

4.2.1 SOLID STATE PROCESSING

Solid state fabrication of Metal Matrix Composites is a of process, in

which Metal Matrix Composites are formed as a result of bonding matrix metal and

dispersed phase due to mutual diffusion occurring between them in solid states at

elevated temperature and under pressure. Low temperature of solid state fabrication

process (as compared to Liquid state fabrication of Metal Matrix Composites)

depresses undesirable reactions on the boundary between the matrix and dispersed

(reinforcing) phases.

There are two principal groups of solid state fabrication of Metal Matrix

Composites:

1. Diffusion bonding

2. Sintering.

4.2.1.1 DIFFUSION BONDING

Diffusion Bonding is a solid state fabrication method, in which matrix in

form of foils and dispersed phase in form of layers of long fibres are stacked in a

particular order and then pressed at elevated temperature.

The finished laminate composite material has a multilayer structure.

Application of pressure and temperature either by hot or cold pressing provides good

bonding between the fibre and the matrix in the perform. This improves the strength

of the composites by introduction of plastic deformation in matrix and removing

voids to densify the composite fully Diffusion Bonding is used for fabrication of

simple shape parts (plates, tubes).

4.2.1.2 SINTERING

Sintering fabrication of Metal Matrix Composites is a process, in which a

powder of a matrix metal is mixed with a powder of dispersed phase in form of

particles or short fibres for subsequent compacting and sintering in solid state

(sometimes with some presence of liquid).

Sintering is the method involving consolidation of powder grains by

heating the “green” compact part to a high temperature below the melting point,

when the material of the separate particles diffuse to the neighbouring powder

particles.

In contrast to the liquid state fabrication of Metal Matrix Composites,

sintering method allows obtaining materials containing up to 50% of dispersed

phase.

Metal Matrix Composites may be deformed also after sintering operation

by rolling, forging, and pressing, Drawing or Extrusion. The deformation operation

may be either cold (below the recrystallization temperature) or hot (above the

recrystallyzation temperature).

Deformation of sintered composite materials with dispersed phase in

form of short fibres results in a preferred orientation of the fibres and anisotropy of

the material properties (enhanced strength along the fibres orientation).

4.2.2 LIQUID STATE PROCESSING

Liquid state fabrication of Metal Matrix Composites involves

incorporation of dispersed phase into a molten matrix metal, followed by its

Solidification.

In order to provide high level of mechanical properties of the composite,

good interfacial bonding (wetting) between the dispersed phase and the liquid matrix

should be obtained.

Wetting improvement may be achieved by coating the dispersed phase

particles (fibres). Proper coating not only reduces interfacial energy, but also

prevents chemical interaction between the dispersed phase and the matrix.

The techniques used for producing cast particulate composites using

liquid metallurgy are Stir casting and Infiltration process

4.2.2.1 STIR CASTING

The simplest and the most cost effective method of liquid state

fabrication is Stir Casting.

Stir Casting is a liquid state method of composite materials fabrication,

in which a dispersed phase (ceramic particles, short fibres) is mixed with a molten

matrix metal by means of mechanical stirring.

The liquid composite material is then cast by conventional casting

methods and may also be processed by conventional Metal forming technologies.

Stir Casting is characterized by the following features:

Content of dispersed phase is limited (usually not more than 30 vol%).

Distribution of dispersed phase throughout the matrix is not perfectly

homogeneous:

1. There are local clouds (clusters) of the dispersed particles (fibres);

2. There may be gravity segregation of the dispersed phase due to a difference in the

densities of the dispersed and matrix phase.

The technology is relatively simple and low cost.

Distribution of dispersed phase may be improved if the matrix is in semi-solid

condition.

The method using stirring metal composite materials in semi-solid state is

called Rheocasting. High viscosity of the semi-solid matrix material enables better

mixing of the dispersed phase.

4.2.2.2 INFILTRATION

Infiltration is a liquid state method of composite materials fabrication, in

which a preformed dispersed phase (ceramic particles, fibres, woven) is soaked in a

molten matrix metal, which fills the space between the dispersed phase inclusions.

The motive force of an infiltration process may be either capillary force

of the dispersed phase (spontaneous infiltration) or an external pressure (gaseous,

mechanical, electromagnetic, centrifugal or ultrasonic) applied to the liquid matrix

phase (forced infiltration).

Gas pressure infiltration

Gas Pressure Infiltration is a forced infiltration method of liquid phase

fabrication of Metal Matrix Composites, using a pressurized gas for applying

pressure on the molten metal and forcing it to penetrate into a preformed dispersed

phase. Gas Pressure Infiltration method is used for manufacturing large composite

parts.

The method allows using non-coated fibres due to short contact time of the

fibres with the hot metal.In contrast to the methods using mechanical force, Gas

Pressure Infiltration results in low damage of the fibres.

Squeeze casting infiltration

Squeeze Casting Infiltration is a forced infiltration method of liquid

phase fabrication of Metal Matrix Composites, using a movable mold part (ram) for

applying pressure on the molten metal and forcing it to penetrate into a performed

dispersed phase, placed into the lower fixed mold part.

Squeeze Casting Infiltration method is similar to the Squeeze casting

technique used for metal alloys casting.

Squeeze Casting Infiltration process has the following steps:

A perform of dispersed phase (particles, fibres) is placed into the lower fixed

mold half.

A molten metal in a predetermined amount is poured into the lower mold half.

The upper movable mold half (ram) moves downwards and forces the liquid

metal to infiltrate the pre form.

The infiltrated material solidifies under the pressure.

The part is removed from the mold by means of the ejector pin.

The method is used for manufacturing simple small parts (automotive engine pistons

from aluminum alloy reinforced by alumina short fibres).

Pressure die infiltration

Pressure Die Infiltration is a forced infiltration method of liquid phase

fabrication of Metal Matrix Composites, using a Die casting technology, when a

preformed dispersed phase (particles, fibres) is placed into a die (mould) which is

then filled with a molten metal entering the die through a sprue and penetrating into

the pre form under the pressure of a movable piston (plunger).

4.2.3 IN-SITU FABRICATION

In situ fabrication of Metal Matrix Composite is a process, in which

dispersed (reinforcing) phase is formed in the matrix as a result of precipitation from

the melt during its cooling and Solidification.

Different types of Metal Matrix Composites may be prepared by in situ

fabrication method:

1. Particulate in situ MMC – Particulate composite reinforced by in situ

synthesized dispersed phase in form of particles.

Examples: Aluminum matrix reinforced by titanium boride (TiB2) particles,

magnesium matrix reinforced by Mg2Si particles.

2. Short-fibre reinforced in situ MMC – Short-fibre composite reinforced by in

situ synthesized dispersed phase in form of short fibres or whiskers (single crystals

grown in form of short fibres).

Examples: Titanium matrix reinforced by titanium boride (TiB2) whiskers,

Aluminum matrix reinforced by titanium aluminide (TiAl3) whiskers.

3. Long-fibre reinforced in situ MMC – Long-fibre composite reinforced by in

situ synthesized dispersed phase in form of continuous fibres.

Example: Nickel-aluminum (NiAl) matrix reinforced by long continuous fibres of

Mo (NiAl-9Mo alloy).

Dispersed phases of in situ fabricated Metal Matrix Composites may

consist of intermetallic compounds, carbides, borides, oxides, one of eutectic

ingredients.

Advantages of in situ Metal Matrix Composites:

In situ synthesized particles and fibres are smaller than those in materials with

separate fabrication of dispersed phase (ex-situ MMCs). Fine particles provide

better strengthening effect;

In situ fabrication provides more homogeneous distribution of the dispersed

phase particles;

Bonding (adhesion) between the particles of in situ formed dispersed phase

and the matrix is better than in ex-situ MMCs;

Equipment and technologies for in situ fabrication of MMCs are less

expensive.

Disadvantages of in situ Metal Matrix Composites:

Choice of the dispersed phases is limited by thermodynamic ability of their

precipitation in particular matrix;

The size of dispersed phase particles is determined by solidification conditions

CHAPTER 5

CRACKS

A crack is a type of fracture that separates a solid body into two, or more, pieces under the action of stress. There are three types of modes of failure [4].

Mode I: The forces are perpendicular to the crack (the crack is horizontal and the forces are vertical), pulling the crack open. This is referred to as the opening mode.

Mode II: The forces are parallel to the crack. One force is pushing the top half of the crack back and the other is pulling the bottom half of the crack forward, both along the same line. This creates a shear crack: the crack is sliding along itself. It is called in-plane shear because the forces are not causing the material to move out of its original plane.

Mode III: The forces are perpendicular to the crack (the crack is in front-back direction, the forces are pulling left and right). This causes the material to separate and slide along itself, moving out of its original plane (which is why it’s called out-of-plane shear).

Figure 5.1 Three Loading Modes

CHAPTER 6

FABRICATION OF COMPOSITES

6.1 SELECTION OF MATERIALS AND COMPOSITION

The base metal is chosen as Aluminium 2024.

The reinforcement is chosen as silicon carbide particulates and Graphite

particulates (SiCp, Gr)

With the base metal as Aluminium, the composite is to be fabricated with 10%

volume of Silicon Carbide Particulates and 5%.of Graphite

6.1.1 Matrix material

Aluminium, the second most abundant metallic element on the earth,

became an economic competitor in engineering applications recently. The metal

matrix selected for present investigation is Al 2024. The chemical composition of

the matrix material is as shown the Table.

Table 6.1 Chemical Composition of Al 2024 (weight %)

Element Si Fe Cu Mn Mg Zn Ti V Zr Al

Nominal

Composition

% ( Weight)

0.50

max

0.50

max

3.8 to

7.90

0.30

to

0.90

1.20

to

1.80

0.25

max

0.15

max

0.15

max

0.15

max

Balance

Actual

Comp%

(Weight)

0.24 0.20 4.43 0.47 1.32 0.07 0.22 0.01 0.01 Balance

The typical Composition of the matrix material is shown in the following table.

Table 6.2 Typical Composition of Al 2024 (weight %)

Element Weight in %

Al 93.50

Cu 4.4

Mg 1.5

Mn 0.6

This matrix was chosen since it provides excellent combination of strength

and damage tolerance at high strength applications like structural components and

high strength weldments. It also has a high heat dissipation capacity due to its high

thermal conductivity.

6.1.2 REINFORCEMENT MATERIALS

SiC particles are the most commonly used reinforcement materials in the

discontinuously reinforced metal-matrix composite system. Aluminum matrix

composites reinforced with SiC particulates provide for a low-cost, high-modulus

material that can be processed via conventional powder metallurgy techniques. With

increased additions of SiC reinforcement, the modulus increases, and losses in

strength, ductility, and toughness may occur. Also, the role of the interfacial bond

between SiC particulates and the aluminum matrix may further detract from the

mechanical properties when the composite is subjected to high temperatures. Particle

size and shape are important factors in determining materials properties. Fatigue

strength is greatly improved with the use of fine particles.

The SiC particles, which were used to fabricate the composite,

had an average particle size of 23 m and average density of 3.2 g / cm3. It is the

second hardest material after diamond with a Mohr’s hardness of 9.5. The melting

point of the SiCp is 2890 0C. The graphite particles used for hybrid composites are

of 45 m size and average density of 2.25 g / cm3. It is a soft material with a

hardness of 1-2 Mohr’s scale, with a melting point of 36500 C. Graphite is a natural

lubricant used in many applications.

6.2 FABICATION METHOD

Since the Al 2024 is found in bulk quantities in the market it is proposed to

first fabricate the Al 2024 metal by using the typical composition as shown in the

table 5.2. The materials are displayed in photographs below.

STIR CASTING

The stir casting technique was used to fabricate the composite specimen

as it ensures a more uniform distribution of the reinforcing particles. This method is

most economical to fabricate composites with discontinuous fibers or particulates. In

this process, matrix alloy (Al 2024) was first superheated above its melting

temperature and then temperature is lowered gradually below the liquidus

temperature to keep the matrix alloy in the semisolid state. At this temperature, the

preheated Sic particles of 10 % (by weight) and graphite particle of average size of

23 µm and 45 µm respectively were introduced into the slurry and mixed using a

graphite stirrer.

The composite slurry temperature was increased to fully liquid state and

automatic stirring was continued to about five minutes at an average stirring speed of

300-350 rpm under protected organ gas. The SiCp particles help in distributing the

graphite particles uniformly throughout the matrix alloy. The melt was then

superheated above liquidus temperature and finally poured into the cast iron

permanent mould for testing specimen. The specification of the fabricated billet

composite is150 mm length and 50 mm width and a thickness of 20 mm

The composite metal after been ejected from the mold is then rolled in a hot

rolling machine up to 15 passes. This is done in order to help in distributing the

silicon carbide particulates in the metal matrix and thereby improving the

mechanical properties. The billet composite, due to hot rolling reduces its thickness

and as an end result edge cracks are being formed.

CHAPTER 7

CONCLUSION

The relevant materials and the selection criteria have been collected and

identified. The type of crack and material properties have been studied in phase –I.

In the phase-II project, the composite metal is fabricated, hot rolled and the

analysis of the fabricated composite with edged cracks is studied and the outcome

will be the solution for different applications of the composite material in the field of

aerospace and automotive industries.

CHAPTER 8

APPENDICES

CHAPTER 9

REFERENCES

Text Books

1. Abis, S., (1989), “Characteristics of an aluminium alloy/Alumina Metal

Matrix composite”, Composites science and technology, Vol.35, pp.1-11.

2. Brian Terry and Jones Glyn.,(1990), Metal matrix composite, Elsevier

Science Publishers Ltd., England, pp.41-47.

3. ASM International, (1993),

“Advanced Materials and Processes”, Vol.143 No.6, p.21.

4. American Foundry men’s Society, Cast metals handbook, 4th ed., Desplaines

(1957).

5. J.J. Sha, J.S. Park, T. Hinoki and A. Kohyama, “Tensile behavior and

microstructural characterization of SiC fibres under loading”, Materials

Science and Engineering: A, Volume 456, Issues 1-2, 15 May 2007, Pages

72-77.

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