Effect Of Particulate Reinforcement On The Wear Properties Of Mg-Al Nano Composite.

UNIVERSITI TEKNIKAL MALAYSIA MELAKA

EFFECT OF PARTICULATE REINFORCEMENT ON THE WEAR

PROPERTIES OF MG-AL NANO COMPOSITE

.

This report submitted in accordance with requirement of the Universiti Teknikal Malaysia Melaka (UTeM) for the Bachelor Degree of Manufacturing Engineering

(Engineering Materials) (Hons.)

by

MUHAMMAD KHAIRUL NIZAM BIN SAAEY B050910124

901123-10-5637

FACULTY OF MANUFACTURING ENGINEERING

2013

UNIVERSITI TEKNIKAL MALAYSIA MELAKA

BORANG PENGESAHAN STATUS LAPORAN PROJEK SARJANA MUDA

TAJUK: Effect of Particulate Reinforcement on The Wear Properties Of Mg-Al Nano Composite.

SESI PENGAJIAN: 2012/ 13 Semest er 2

Saya MUHAMMAD KHAIRUL NIZAM BIN SAAEY

mengaku membenarkan Laporan PSM ini disimpan di Perpust akaan Universit i Teknikal Mal aysia Mel aka (UTeM) dengan syarat -syarat kegunaan sepert i berikut :

1. Laporan PSM adal ah hak mil ik Universit i Teknikal Mal aysia Mel aka dan penul is. 2. Perpust akaan Universit i Teknikal Mal aysia Mel aka dibenarkan membuat sal inan unt uk

t uj uan pengaj ian sahaj a dengan izin penul is.

3. Perpust akaan dibenarkan membuat sal inan l apor an PSM ini sebagai bahan pert ukaran ant ara inst it usi pengaj ian t inggi.

SULIT

TERHAD

TIDAK TERHAD

(Mengandungi makl umat yang berdarj ah kesel amat an at au kepent ingan Mal aysiasebagaimana yang t ermakt ub dal am AKTA RAHSIA RASMI 1972)

(Mengandungi makl umat TERHAD yang t el ah dit ent ukan ol eh organisasi/ badan di mana penyel idikan dij al ankan)

Al amat Tet ap:

313, JLN KEJORA 2H/ 1, KG MELAYU RASA TAMBAHAN 44200 RASA, SELANGOR

Tarikh: _________________________

Disahkan ol eh:

Cop Rasmi:

Tarikh: _________________________ ** Jika Laporan PSM ini SULIT at au TERHAD, sil a lampirkan surat daripada pihak berkuasa/ organisasi berkenaan dengan menyat akan sekal i sebab dan t empoh l aporan PSM ini perl u dikelaskan sebagai SULIT at au TERHAD.

DECLARATION

I hereby, declared this report entitled “

Effect Of Particulate Reinforcement On

The Wear Properties Of Mg-Al Nano Composite

” is the results of my own research except as cited in references.

Signature :……….

Author’s Name : MUHAMMAD KHAIRUL NIZAM BIN SAAEY

APPROVAL

This report is submitted to the Faculty of Manufacturing Engineering of UTeM as a partial fulfillment of the requirements for the degree of Bachelor of Manufacturing Engineering (Engineering Materials) (Hons.). The members of the supervisory committee are as follow:

……… (PROF. DR. QUMRUL AHSAN)

……… (CHANG SIANG YEE)

ABSTRAK

Sejak tiub nano karbon telah dijumpai, bahan-bahan ini telah menjadi faedah yang akan digunakan sebagai tetulang di dalam matriks logam kerana sifat unggul. Oleh itu, nanotube karbon (CNT) dalam saiz nano diperkukuh komposit matriks magnesium dijangka mempunyai banyak aplikasi dalam industri aeroangkasa, kapal terbang, kereta dan elektronik. Dalam kajian ini, magnesium komposit matriks logam yang mengandungi beberapa peratusan berat nanotube karbon telah disediakan dengan menggunakan kaedah metalurgi serbuk diikuti dengan proses penyemperitan. Seperti yang semakin meningkat peratusan berat (% berat) CNT, kepadatan dan kekerasan sifat-sifat bahan yang semakin meningkat. Ini kerana lebih padat CNT berbanding dengan matriks aloi magnesium dan peningkatan pemindahan beban di antara matriks dan CNT akibat pembentukan karbida (Al2MgC2). Kadar memakai

khusus yang telah mengurangkan sebagai semakin meningkat% berat MWCNT kerana tingkah laku diri pelincir CNT yang akan membantu untuk mengurangkan kawasan sentuhan antara pin dan permukaan cakera. Pada kelajuan gelongsor 0.5 m / s, mekanisme haus itu lelasan mana alur dan calar boleh dilihat di bawah imej SEM. Meningkatkan kelajuan gelongsor kepada 2.5 m / s alur mempunyai perubahan kepada alur cetek kerana cara memotong untuk membajak berubah. Dan meningkatkan kelajuan tergelincir kepada 4.5 m / s, mekanisme rekatan telah berlaku di mana barisan parit dan plastik ubah bentuk dapat dilihat. Penurunan terma dan retak keletihan juga telah berlaku pada kelajuan gelongsor ini. Oleh itu CNT telah membantu meningkatkan kekerasan dan memakai sifat-sifat matriks logam komposit jika CNT tersebar baik di dalam komposit.

ABSTRACT

Since Carbon Nanotube had been found, these materials have become the interest to be used as reinforcement inside metal matrix due to its superior properties. Thus, carbon nanotube (CNT) in nano size reinforced magnesium matrix composites are expected to have many applications in aerospace, aircraft, automobile and electronic industries. In this study, magnesium metal matrix composites containing several weight percentages of carbon nanotube were prepared by using powder metallurgy method followed by extrusion process. As increasing of the weight percentage (weight %) of the CNT, the density and hardness properties of material were increasing. This due to the denser CNT compared to the magnesium alloy matrix and the improvement of load transfer between matrix and CNT due to formation of carbide (Al2MgC2). The specific wear rate was reduced by increasing weight % of

CNT due to the self-lubricating behavior of the CNT that will help to reduce the contact area between pin and disk surface. At sliding speed of 0.5 m/s, the wear mechanism was abrasion where deep groove and scratch can be seen below SEM image. Increasing of sliding speed of 2.5 m/s the deep groove has changed to shallow groove due to changing mode of cutting to ploughing. And increasing the sliding speed to 4.5 m/s, the adhesion mechanism has occurred where the row of furrow and plastic deformation can be seen. Thermal softening and fatigue crack also has happened at this sliding speed. Thus the CNT has helped to improve the hardness and wear properties of the metal matrix composite if the CNT dispersed well inside the composite.

DEDICATION

To my beloved parents and siblings.

ACKNOWLEDGEMENT

Apart from this effort, this study entitled “Effect of particulate reinforcement on the wear properties of Mg-Al Nano Composite” is successfully done within the time given. I would like to take this opportunity to express my gratitude to the people who have been given their support in accomplishing this thesis.

I am grateful and would like to express my sincere gratitude to my supervisor, Prof. Dr. Qumrul Ahsan, Miss Chang Siang Yee and Mr. Tee Zhen Wei for their ideas and suggestions, invaluable guidance, continuous encouragement, them tolerance of my naïve mistakes and constant support. I would like to acknowledge all them comments and suggestions, which was crucial for the successful completion of this thesis. They have also been abundantly helpful and have assisted me in numerous ways.

I am indebted to all the lecturers and technicians who have taught me since I entered to University Technical Malaysia Melaka (UTeM) for giving me a stimulating and pleasant environment in which to learn and grow. My sincere thanks go to all my friends, who helped me directly and indirectly in completing this thesis and also for their contribution, inspirations and supports during doing this thesis.

Finally, yet importantly, I would like to express my indebtedness and heartfelt thanks to my beloved parents for their blessings, love, dream and sacrifice throughout my life. I acknowledge the sincerity of my family who consistently encouraged me to carry on my studies until this level. I cannot find the appropriate words that could properly describe my appreciation for their devotion, support and faith in my ability to attain my goals.

TABLE OF CONTENT

Abstrak i

Abstract ii

Dedication iii

Acknowledgement iv

Table of Contents v

List of Tables viii

List of Figures ix

List of Abbreviations, Symbols and Nomenclature xii

CHAPTER 1 INTRODUCTION 1

1.1 Research Background 1

1.2 Problem Statement 3

1.3 Objectives 4

1.4 Scope of the Study 4

CHAPTER 2 LITERATURE REVIEW 5

2.1 Composite 6

2.1.1 Metal Matrix Composite 7

2.1.1.1 Metal Matrix 8

2.1.1.1 (a) Ferrous Metal Matrix 8

2.1.1.1 (b) Non-ferrous Metal Matrix 9 2.1.1.1 (b) i) Magnesium Alloy Matrix 10

2.1.1.2 Reinforcement in MMC 13

2.1.1.2 (a) Carbon Nanotube as Reinforcement 15

2.2 Fabrication of Metal Matix Composite 18

2.2.1 MMC fabrication by Powder Metallurgy Route 19

2.3 Material Properties 21

2.3.1 Hardness Properties 21

2.3.1.1 Vickers Hardness 22

2.3.2 Wear Properties 23

2.3.2.1 Wear Mechanism 26

2.3.2.1 (a) Abrasive Wear 26

2.3.2.1 (b) Corrosive Wear 27

2.3.2.1 (c) Adhesive Wear 28

2.3.2.1 (d) Fatigue Wear 28

CHAPTER 3 METHODOLOGY 30

3.1 Raw Material 30

3.1.1 Magnesium Alloy Powder 30

3.1.2 Carbon Nanotube (CNT) 31

3.2 Characterization of Raw Material 32

3.2.1 Particle Siza Analyzer (PSA) 32

3.3 Powder Metallurgy Route 33

3.3.1 Blending and Mixing 34

3.3.2 Cold Pressing 35

3.3.3 Sintering 37

3.3.4 Extrusion 37

3.4 Mechanical Test 41

3.4.1 Vickers Hardness Test 41

3.4.2 Pin on Disk Wear Test 42

3.4.3 The Flow Chart of Methodology 45

CHAPTER 4 RESULT AND DISCUSSION 46

4.2 Particle Size Analysis 47

4.3 Density Measurement 48

4.4 Void Content 48

4.5 Hardness 51

4.6 Tribology Test (Pin on Disk) 53

4.6.1 Specific Wear Rate 54

4.6.2 Coefficient of Friction 56

4.6.3 Wear Mechanism 59

4.6.3.1 Effect of CNT weight% 59

4.6.3.2 Effect of Sliding Speed 61

CHAPTER 5 CONCLUSION AND FUTURE WORKS 67

5.1 Conclusion 66

5.2 Future Works / Suggestions 67

REFERENCES 68

LIST OF TABLES

2.1 Some example of ferrous metal composite with its application

(Callister W. D., 2008). 8

2.2 Some example of ferrous metal composite with its application

(Callister W. D., 2008). 9

2.3 Some magnesium cast and wrought alloys typical composition

(wt%) (Buldum B. B. et al). 11

2.4 Typical reinforcement material for MMCs 13

2.5 Properties of pure magnesium, magnesium reinforced nano alumina particle, magnesium-aluminium alloy and

magnesium reinforced micro sized silicon carbide particle.

(Lim C.Y.H et al, 2005)(Park H. Y. et al, 2008). 16

3.1 Constituent of element magnesium aluminium powder

(KFO France Co., Ltd) 30

3.2 Properties of carbon nanotubes ( MSDS of Nanostructured &

Amorphous Materials, Inc., USA). 31

3.3 The composition of metal matrix composite by their constituent

Weight percent 35

4.1 Table of density with different composition of MWCNT 47 4.2 Table of void content for different composition of

MWCNT 49

4.3 Table of Vickers Hardness for different composition of

MWCNT 51

4.4 Table of Specific Wear Rate for different composition

of MWCNT 54

4.5 Table of Specific Wear Rate for different composition

of MWCNT 57

LIST OF FIGURES

2.1 Overview on literature review in this study 5

2.2 The division of composite based on it matrix and reinforcement 6 2.3 Marking magnesium alloys (Buldum B. B. et al). 11 2.4 Aluminum - magnesium binary phase diagram (ASM Handbook). 13 2.5 Secondary electron SEM micrograph of the CNTs used as

reinforcement material for composite materials

(Bustamante R. P. et al, 2012). 15

2.6 SEM image of fracture surface of Mg-2wt%MWCNTs. Homogeneous dispersion of MWCNTs in Mg matrix

(Bustamante R. P. et al, 2012). 15

2.7 Results from microhardness test of the Al2024–CNTs

composites. By comparison pure Al and the Al2024 hardness

values under several processing conditions are displayed.

(Bustamante R. P. et al, 2012). 23

2.8 Schematic process of the pin-on-disc apparatus to study the wear behaviour of the Al2024–CNTs composites.

Samples slide against the abrasive SiC paper at two

different loads. (Bustamante R. P. et al, 2012). 25 2.9 Grooves and scratch marks on the pin surface indicating abrasion.

(Lim C.Y.H et al, 2005) 27

2.10 The appearance of the aluminium alloy surface after its corrosive wear in the acid rain

(Pokhmurskii V.I. et al, 2011). 27

2.11 Schematic diagram showing on (a) adhesive wear

(b) oxidative wear (Kumar A. and Singh S., 2011). 30 2.12 Schematic on fatigue wear on metal material

(Kumar A. and Singh S., 2011). 29

3.1 Macroview of magnesium aluminium alloys powder 30

3.2 Macroview of multi-walled carbon nanotubes. 31 3.3 Scirocco Mastersizer 2000 Particle Size Analyzer 32 3.4 The powder metallurgy sequence for Magnesium alloys

composite 33

3.5 Planetary Ball Mill Machine (model: Insmart) 34

3.6 Analytical Balance Excellent (Model: Mettler Toledo) 34

3.7 150 Ton Hydraulic Press Machine 35

3.8 The front view of punch and die for cold compaction process 36 3.9 The top view of punch and die for cold compaction process 36 3.10 The green compact pallet formed after compaction process 36 3.11 (a) LT Horizontal Tube Furnace (Model: TF70-1600) (b) Sintering

graph 37

3.12 Front view of plunger and die for extrusion process 38 3.13 Top view of plunger and die for extrusion process. 38

3.14 The extruded specimen. 38

3.15 Metkon Micracut 125 Diamond Cutters. 39

3.16 The BUEHLER Beta Twin Variable Speed Grinder-Polisher 39 3.17 The specimen for density, hardness and wear test. 39 3.18 The Electronic Densimeter MD-300S (AlfaMirage, Japan) 40 3.19 The Mitutoyo Mvk-Micro Vickers Hardness Testing Machines 41 3.20 The Ducom TR-20LE Pin-on –Disc wear testing machine. 43 3.21 The controller of the wear and friction-testing machine. 43 3.22 Scanning Electron Microscope (SEM) Zeiss Evo® 50 model 44

4.1 Particle size result for Magnesium alloy powder. 46 4.2 The graph of density versus composition for the metal matrix

composite 47

4.3 The graph of void content versus composition for the metal

matrix composite 49

4.4 The graph of Vickers Hardness versus composition for the metal

matrix composite 51

4.5 The macro view of the worn surface on pin surface 53

4.6 The graph of Specific Wear Rate versus sliding speed for

various composition metal matrix composite 54

4.7 The wear temperature of metal matrix composite. 56 4.8 The Coefficient of Frictionof the Metal Matrix Composite 57 4.9 The Scanning Electron Microscope (SEM) on the worn surface

of the Metal Matrix Composite for sliding speed of 4.5 m/s,

sliding distance of 5000 m and applied load of 40 N . 59 4.10 The Scanning Electron Microscope (SEM) on the worn surface

of the Metal Matrix Composite for 0.5 wt% of CNT with

sliding distance of 500 m and applied load of 40 N. 61

4.11 Fatigue crack happen at high sliding speed 62

4.12 The EDX analysis that show present of oxide element

at the fatigue crack area. 63

4.13 The mechanically mixed layer (MML) on the pin surface

due to thermal softening. 64

4.14 The EDX analysis shows the presence of Fe, Al, O and

Mg on MML area 64

4.15 The protruding at the edge of the pin indicate thermal

softening mechanism 65

LIST OF ABBREVIATIONS, SYMBOLS AND

NOMENCLATURES

MMC - Metal Matrix Composite

CMC - Ceramic Matrix Composite

PMC - Polymer Matrix Composite

PM - Powder Metallurgy

HCP - Hexagonal Closed Packed

SEM - Scanning Electron Microscope

PSA - Particle Size Analyzer

ASTM - American Standard Test Method

XRD - X-Ray Diffraction

Mg - Magnesium

SiC - Silicon Carbide

Al2O3 - Alumina

CNT - Carbon Nanotube

SWNT - Single Wall Carbon Nanotube

MWNT - Multi Wall Carbon Nanotube

Al - Aluminium

Ti - Titanium

C - Carbon

W - Tungsten

WC - Tungsten Carbide

Cu - Copper

B - Boron

Si - Silicon

ºC - Degree Celcius

Q - Total volume of wear debris produced

W - Total normal load

H - Hardness of the softest contacting surfaces

K - Dimensionless constant

L - Sliding distance

HV - Vickers hardness

F - Load in kgf

d - Arithmetic mean of two diagonals, d1 and d2 in mm m2 - mass (g) of the specimen after testing

m1 - initial mass (g) of the specimen

� - density (g/mm3) of the specimen

FN - normal load (N) applied on the specimen during sliding

SD - total sliding distance (m)

T - theoretical composite density

D - Density of resin

d - Density of reinforcement

R - Resin weight %

r - Reinforcement weight %

V - Void content (volume %)

Td - theoretical composite density

Md - measured composite density

Wt% - weight percentage (%)

CHAPTER 1

INTRODUCTION

1.1 Research Background

The composite can be defined as a mixture of two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct on a macroscopic level within the finished structure. This composite is fabricated to improve the properties of conventional or pure material. Composite has been used in almost all areas of industries due to its advantages over the conventional material. Since the development of metal matrix composite (MMC) for the past three decades, this material has been used in a wide range of application especially in aerospace and automotive application. MMC has advantage of high strength material and can be used in high temperature application. MMC usually been reinforced with ceramic reinforcement such as silicon carbide (SiC) and Alumina (Al2O3). For light

weight application, a light metal group such as aluminium, magnesium and titanium are most considered. Mostly used light metal is aluminium and titanium. But due to increasing fuel price nowadays, magnesium has been considered to replace other light metal due to its light weight which is about 2/5 and 3/5 as much as similar volumes of zinc base and aluminium base alloys (Khanna O. P., 2004).

Besides lightweight, advantages of magnesium are good mechanical damping properties, good castability especially in die casting process and also plentiful of global supply. Despite of its advantages, magnesium when compared with aluminium, it has low strength and ductility, poor wear, creep and corrosion resistance (Tjong S. C., 2009). Thus to overcome this problem, magnesium reinforces with ceramic micro and nano particle. In general, MMC been reinforce with micro size reinforcement. Lately, there is extensive interest in the production of metal matrix nanocomposite in which nano particulates are incorporated in base matrix. When compared to composites with micron-sized reinforcements, nanocomposites exhibit comparable or better mechanical properties with the use of lesser amount of nanoparticulate reinforcements. Some nano reinforcement that's been used is nano size alumina particle and carbon nanotube (CNT). Alam M. E. et al, (2011) has found that the nanoparticulate alumina has increased the mechanical properties of magnesium alloy AZ31such as hardness, yield strength and ultimate tensile strength.

A key challenge in the processing of composites is to evenly distribute the reinforcement phases to attain a defect-free microstructure. Based on the shape, the reinforcing phases in the composite can be either particles or fibers. The reasonably low material cost and suitability for automatic processing has made the particulate-reinforced composite preferable to the fiber-particulate-reinforced composite for automotive applications (YE H. Z. et al, 2004). One of the main processing of MMC is powder metallurgy. Powder metallurgy is a net shape forming process consisting of producing metal powder, blending them, compacting them indies, and sintering them to impart strength, hardness and toughness. Although the size and the weight of its products are limited, the PM process is capable of producing relatively complex parts economically, in the net shape form and a wide variety of metal and alloy powders. Basically, in the conventional PM production, after the metallic powders have been produced, the sequence consists of three steps. Firstly, blending and mixing the powder, and then compaction, in which the powders are pressed into the desired part shape. The last step of PM method is sintering, which involves heating to a temperature below the melting point to cause solid state bonding of the particles and strengthening the part.

Due to the magnesium alloy application are in moving parts or engine parts, wear is a serious problem happened to this material. Although wear only happens at the surface, it can undermine the mechanical function of the parts. It can cause structural failure on the part and make early replacement of the part or component. There were several wear mechanisms such as abrasion, adhesion, delamination, thermal softening and melt. Magnesium and aluminium based metal matrix composites (MMCs) are prone to suffer wear by delamination, since the discontinuity at the interface between reinforcement and matrix promote crack nucleation and propagation, which are central to the mechanics of delamination. (Lim C. Y. H et al, 2005)

1.2 Problem Statement

Magnesium has been found the lightest metal available on earth. So it can be used for application where light weight is the main consideration such as in automotive and aerospace. But this material has its limitation when compared with other light weight material such as aluminium and titanium such as low strength and ductility, poor wear, creep and corrosion resistance. In order to overcome the problem, nano filler added as the reinforcement in the magnesium matrix to produce a metal matrix composite. In this study, the effect of the nano size reinforcement on the hardness and wear properties of the metal matrix composite is the main concern objective. From recent research, it has been believed that the nano fillers are the main character to improve the properties of the composite. Although with small amounts, it can give big impact to the hardness and wear properties of the material if it is well dispersed inside the material. The high tendency agglomeration of this CNT due to strong Van Der Waal forces will reduce the properties of the composite. This research studies the effect of nano sized reinforcement on the hardness and wear properties of metal matrix composite.

1.3 Objective

The objectives of the present study are:

1. To prepare a magnesium alloy metal matrix composite with different volume fraction of carbon nanotubes (CNT) reinforcement using powder metallurgy route.

2. To characterize the physical properties of magnesium alloy metal matrix composite with different volume fraction of carbon nanotubes (CNT) by using the Vickers hardness test.

3. To investigate the wear behaviour of magnesium alloy metal matrix composite with different volume fraction of carbon nanotubes (CNT) by using pin on disk wear test.

1.4 Scope

In this study, the fabrication of the magnesium hybrid metal matrix composite specimen will undergo a powder metallurgy route. The powder metallurgy route consists of bending/mixing, compaction and sintering. The reinforcement composition that will be used is 0.0, 0.5, and 1.0 wt. % for carbon nanotube. This study will investigate the hardness and wear behaviour of the magnesium alloy metal matrix composite with a different weight percent (wt.%) of the carbon nanotube reinforcement. The hardness test that's been used is Vickers hardness test with diamond indenter. The pin-on-disk wear test will be used to observe the wear rate and coefficient of friction of the material. Moreover, the wear morphology of the material will be studied to observe the wear mechanism of the material by using scanning electron microscope. The wear morphology consists of worn surface and also the wear debris.

CHAPTER 2

LITERATURE REVIEW

A literature review of previous research work in various areas which is relevant to this research is presented in this chapter. It consists about the material (matrix and reinforcement) and also on the properties of the material (hardness and wear)

`

Figure 2.1: Overview on literature review in this study COMPOSITE

PMC MMC

CMC

Mg Matrix Non-Ferrous Ferrous

Powder Metallurgy

CNT reinforcement

Hardness Wear

Pin on Disk Vickers

Hardness

2. 1 Composite

A composite material is a non-uniform solid consisting of two or more different materials that are mechanically or metallurgical bonded together. They are mostly formed by the combination of two different materials separated by a distinct interface. Composite is important when the properties of monolithic material are not able to match with expected properties. These composite materials have offered significant improvement of performance compared to monolithic material. The two phases that make up a composite are known as reinforcing phase and matrix phase. The reinforcing phase is embedded in the matrix phase and mainly provides strength to the matrix. Matrix can be divided into three groups which is polymer matrix composite (PMC), metal matrix composite (MMC) and also ceramic matrix composite (CMC) as shown in figure 2.2. For the reinforcement, it can be divided into three groups which are particles (dispersion strengthened or large particles), fibers (discontinuous short or continuous aligned) and structural (laminates and sandwich structures).

Figure 2.2: The division of composite based on its matrix and reinforcement

Ceramic are widely used in high temperature application such as in aerospace and automotive where polymer is widely used in structural application. However this material is heavy that will contribute in increasing use of energy resource such as fuel or oil. In the last few years, a significant increase in applications of MMCs has taken place, particularly in the areas of automotive, aerospace, electronics, and recreation.

Composite

Reinforcement Matrix

MMC CMC PMC Particles Fibers Structural

2.1.1 Metal Matrix Composite (MMC)

Matthews F. L. and Rawlings R. D. (1999) has stated that the production of ceramic fiber such as boron and silicon carbide in the 1960s and early 1970s has enabled the reinforcement of light metal such as aluminium in aerospace application in a space shuttle and military aircraft to be considered seriously. Monolithic metal is very heavy in weight and cost of production is expensive due to the material being used is 100% monolithic material. Besides that, the maximum operating temperature of the monolithic material is very low that restrict it to being used in high temperature application. The mechanical properties such as ductility of the monolithic metal are very high and low in strength. This restricts the metals to be used in structural applications. Instead been used in monolithic form, this metal reinforced with the ceramic type reinforcement to enhance and improve the properties of the monolithic metals.

Recently, metal matrix composite (MMC) has become increasingly used for application in automotive and aerospace application when compare with PMC and CMC due to their high specific modulus, strength and thermal stability and damping. The main advantages that MMCs possess over CMCs are the usability at high temperatures, and resistance to corrosion by organic fluids. When comparing with most PMC, MMC has certain superior mechanical properties, such as higher transverse and stiffness, higher shear and compressive strength and high temperature capability (Matthews and Rawlings., 1999).

Moreover, composite composition of metals is flexible in constituent so that we can control the properties of the material. But the limitations of metal matrix composite are the fabrication cost and material cost is expensive when compared to PMC. The wide applications of MMC are in aerospace and automotive application. Automobile manufacture has begun using MMC the automobile part such as an engine component that used aluminium alloy matrix been reinforcing with aluminium oxide and carbon fiber.

Besides lightweight, advantages of magnesium are good mechanical damping properties, good castability especially in die casting process and also plentiful of global supply. Despite of its advantages, magnesium when compared with aluminium, it has low strength and ductility, poor wear, creep and corrosion resistance (Tjong S. C., 2009). Thus to overcome this problem, magnesium reinforces with ceramic micro and nano particle. In general, MMC been reinforce with micro size reinforcement. Lately, there is extensive interest in the production of metal matrix nanocomposite in which nano particulates are incorporated in base matrix. When compared to composites with micron-sized reinforcements, nanocomposites exhibit comparable or better mechanical properties with the use of lesser amount of nanoparticulate reinforcements. Some nano reinforcement that's been used is nano size alumina particle and carbon nanotube (CNT). Alam M. E. et al, (2011) has found that the nanoparticulate alumina has increased the mechanical properties of magnesium alloy AZ31such as hardness, yield strength and ultimate tensile strength.

A key challenge in the processing of composites is to evenly distribute the reinforcement phases to attain a defect-free microstructure. Based on the shape, the reinforcing phases in the composite can be either particles or fibers. The reasonably low material cost and suitability for automatic processing has made the particulate-reinforced composite preferable to the fiber-particulate-reinforced composite for automotive applications (YE H. Z. et al, 2004). One of the main processing of MMC is powder metallurgy. Powder metallurgy is a net shape forming process consisting of producing metal powder, blending them, compacting them indies, and sintering them to impart strength, hardness and toughness. Although the size and the weight of its products are limited, the PM process is capable of producing relatively complex parts economically, in the net shape form and a wide variety of metal and alloy powders. Basically, in the conventional PM production, after the metallic powders have been produced, the sequence consists of three steps. Firstly, blending and mixing the powder, and then compaction, in which the powders are pressed into the desired part shape. The last step of PM method is sintering, which involves heating to a temperature below the melting point to cause solid state bonding of the particles and strengthening the part.

Due to the magnesium alloy application are in moving parts or engine parts, wear is a serious problem happened to this material. Although wear only happens at the surface, it can undermine the mechanical function of the parts. It can cause structural failure on the part and make early replacement of the part or component. There were several wear mechanisms such as abrasion, adhesion, delamination, thermal softening and melt. Magnesium and aluminium based metal matrix composites (MMCs) are prone to suffer wear by delamination, since the discontinuity at the interface between reinforcement and matrix promote crack nucleation and propagation, which are central to the mechanics of delamination. (Lim C. Y. H et al, 2005)

1.2 Problem Statement

Magnesium has been found the lightest metal available on earth. So it can be used for application where light weight is the main consideration such as in automotive and aerospace. But this material has its limitation when compared with other light weight material such as aluminium and titanium such as low strength and ductility, poor wear, creep and corrosion resistance. In order to overcome the problem, nano filler added as the reinforcement in the magnesium matrix to produce a metal matrix composite. In this study, the effect of the nano size reinforcement on the hardness and wear properties of the metal matrix composite is the main concern objective. From recent research, it has been believed that the nano fillers are the main character to improve the properties of the composite. Although with small amounts, it can give big impact to the hardness and wear properties of the material if it is well dispersed inside the material. The high tendency agglomeration of this CNT due to strong Van Der Waal forces will reduce the properties of the composite. This research studies the effect of nano sized reinforcement on the hardness and wear properties of metal matrix composite.

1.3 Objective

The objectives of the present study are:

1. To prepare a magnesium alloy metal matrix composite with different volume fraction of carbon nanotubes (CNT) reinforcement using powder metallurgy route.

2. To characterize the physical properties of magnesium alloy metal matrix composite with different volume fraction of carbon nanotubes (CNT) by using the Vickers hardness test.

3. To investigate the wear behaviour of magnesium alloy metal matrix composite with different volume fraction of carbon nanotubes (CNT) by using pin on disk wear test.

1.4 Scope

In this study, the fabrication of the magnesium hybrid metal matrix composite specimen will undergo a powder metallurgy route. The powder metallurgy route consists of bending/mixing, compaction and sintering. The reinforcement composition that will be used is 0.0, 0.5, and 1.0 wt. % for carbon nanotube. This study will investigate the hardness and wear behaviour of the magnesium alloy metal matrix composite with a different weight percent (wt.%) of the carbon nanotube reinforcement. The hardness test that's been used is Vickers hardness test with diamond indenter. The pin-on-disk wear test will be used to observe the wear rate and coefficient of friction of the material. Moreover, the wear morphology of the material will be studied to observe the wear mechanism of the material by using scanning electron microscope. The wear morphology consists of worn surface and also the wear debris.

CHAPTER 2

LITERATURE REVIEW

A literature review of previous research work in various areas which is relevant to this research is presented in this chapter. It consists about the material (matrix and reinforcement) and also on the properties of the material (hardness and wear)

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Figure 2.1: Overview on literature review in this study COMPOSITE

PMC MMC

CMC

Mg Matrix Non-Ferrous Ferrous

Powder Metallurgy

CNT reinforcement

Hardness Wear

Pin on Disk Vickers

Hardness

2. 1 Composite

A composite material is a non-uniform solid consisting of two or more different materials that are mechanically or metallurgical bonded together. They are mostly formed by the combination of two different materials separated by a distinct interface. Composite is important when the properties of monolithic material are not able to match with expected properties. These composite materials have offered significant improvement of performance compared to monolithic material. The two phases that make up a composite are known as reinforcing phase and matrix phase. The reinforcing phase is embedded in the matrix phase and mainly provides strength to the matrix. Matrix can be divided into three groups which is polymer matrix composite (PMC), metal matrix composite (MMC) and also ceramic matrix composite (CMC) as shown in figure 2.2. For the reinforcement, it can be divided into three groups which are particles (dispersion strengthened or large particles), fibers (discontinuous short or continuous aligned) and structural (laminates and sandwich structures).

Figure 2.2: The division of composite based on its matrix and reinforcement

Ceramic are widely used in high temperature application such as in aerospace and automotive where polymer is widely used in structural application. However this material is heavy that will contribute in increasing use of energy resource such as fuel or oil. In the last few years, a significant increase in applications of MMCs has taken place, particularly in the areas of automotive, aerospace, electronics, and recreation.

Composite

Reinforcement Matrix

MMC CMC PMC Particles Fibers Structural

2.1.1 Metal Matrix Composite (MMC)

Matthews F. L. and Rawlings R. D. (1999) has stated that the production of ceramic fiber such as boron and silicon carbide in the 1960s and early 1970s has enabled the reinforcement of light metal such as aluminium in aerospace application in a space shuttle and military aircraft to be considered seriously. Monolithic metal is very heavy in weight and cost of production is expensive due to the material being used is 100% monolithic material. Besides that, the maximum operating temperature of the monolithic material is very low that restrict it to being used in high temperature application. The mechanical properties such as ductility of the monolithic metal are very high and low in strength. This restricts the metals to be used in structural applications. Instead been used in monolithic form, this metal reinforced with the ceramic type reinforcement to enhance and improve the properties of the monolithic metals.

Recently, metal matrix composite (MMC) has become increasingly used for application in automotive and aerospace application when compare with PMC and CMC due to their high specific modulus, strength and thermal stability and damping. The main advantages that MMCs possess over CMCs are the usability at high temperatures, and resistance to corrosion by organic fluids. When comparing with most PMC, MMC has certain superior mechanical properties, such as higher transverse and stiffness, higher shear and compressive strength and high temperature capability (Matthews and Rawlings., 1999).

Moreover, composite composition of metals is flexible in constituent so that we can control the properties of the material. But the limitations of metal matrix composite are the fabrication cost and material cost is expensive when compared to PMC. The wide applications of MMC are in aerospace and automotive application. Automobile manufacture has begun using MMC the automobile part such as an engine component that used aluminium alloy matrix been reinforcing with aluminium oxide and carbon fiber.