development of ceramic cutting tool insert of

DEVELOPMENT OF CERAMIC CUTTING TOOL INSERT OF ALUMINA (Al2O3) AND ZIRCONIA (ZrO2) FOR TURNING

HARDENED TOOL STEEL

ZURAIDY BIN SHAMSUDIN

UNIVERSITI TEKNOLOGI MALAYSIA

iii

Kepada isteri saya yang disayangi: Norafidah Bt Adanan

Anak-anak saya: Noralya dan Muhammad Zahrin

Ibu saya: Che Puan Bt Abd Hamid

Kawan-kawan saya

TERIMA KASIH atas segala jasa dan sokongan yang telah diberikan

iv

ACKNOWLEDGENT

I would like to express my sincere appreciation to my supervisor Assoc. Prof. Dr.

Safian Sharif for his guidance, encouragement and patience throughout this master

project. I also would like to thank to UTM lecturer, Japan-Malaysia Technical Institute

staff and who have contributed to the success of this project.

v

ABSTRAK

Proses penghasilan mata alat dengan kaedah teknologi serbuk adalah satu kaedah

yang digunakan secara meluas pada masa kini terutama untuk mata alat yang diperbuat

daripada bahan seramik. Teknologi serbuk yang digunakan melibatkan tiga kaedah

utama dimana yang pertama bahan mentah akan dijadikan serbuk bersaiz nanometer,

kemudian proses yang kedua, serbuk akan dipadatkan dengan menggunakan acuan dan

tekanan tinggi dan yang ketiga serbuk yang telah dibentuk dengan proses pemadatan

akan di bakar atau ‘sintered’ dengan suhu yang tinggi mengikut jenis bahan yang

digunakan. Di dalam kajian ini, dua serbuk seramik bersaiz nanometer akan

dicampurkan mengikut komposisi yang bersesuaian untuk menghasilkan produk akhir

yang mempunyai ciri-ciri yang lebih baik. Konsep pembuatan ini adalah bersamaan

dengan penghasilan bahan ‘Ceramic Matrix Composite’ dimana satu bahan penguat atau

‘reinforce’ dimasukkan kedalam bahan asas seramik atau ‘ceramic matrix’ untuk

menguatkan atau memperbaiki sifat-sifat keseluruhan bahan tersebut. Untuk proses

pembakaran pula terdapat beberapa proses yang boleh digunakan misalnya pembakaran

dengan menggunakan ‘normal sintering furnace’ iaitu furnace biasa tanpa tekanan dan

vacum, ‘hot isostatic furnace’ yang menggunakan tekanan semasa pembakaran dan

‘vacum sintering furnace’ yang menggunakan vacum semasa pembakaran. Produk akhir

yang dihasilkan dengan kaedah ini akan mempunyai ketumpatan, kekuatan dan

kekerasan yang tinggi, sesuai untuk penggunaannya sebagai mata alat pemotong.

vi

ABSTRACT

The production of cutting tool insert using a powder technology is a process that

is widely use today especially for ceramic cutting tool. The powder technology that has

been use involve three phases which is, firstly the raw material will be grind to

nanometer size powder. In second phase, the powder will be compacted using special

mold with high pressure, and after that sintering process will take place for the third

phase. In this study, two nanometer size ceramic powders will be mixed together with a

suitable composition to produce a better final product. This production concept is

similarly with the production of ‘ceramic matrix composite’ material which is the

reinforce material will be added to the ceramic base material or ceramic matrix. There

are several sintering process that can be use for this study, for example, normal sintering

process, and hot isocratic process with high pressure furnace.

vii

CONTENTS

CHAPTER TOPIC PAGE

TITLE i

DECLARATION ii

DEDICATION iii

ACKNOWLEDGENT iv

ABSTRAK v

ABSTRACT vi

CONTENTS vii

LIST OF TABLES xi

LIST OF FIGURES xii

LIST OF APPENDICES xv

1 INTRODUCTION

1.1 General Background

1.2 Problem Statement

1.3 Objective

1.4 Scope of the Project

1.5 Expected Results

2 LITERATURE REVIEW

2.1 Introduction

2.2 Ball milling

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2.3 Hot Isostatic Press

2.4 Ceramic material

2.4.1 Properties of ceramic

2.5 Alumina powder

2.5.1 Properties of alumina powder

2.6 Zirconia powder

2.7 Zirconia toughened alumina (ZTA) cutting tools

2.8 Commercial ZTA product

2.8.1 Morgan Advance Ceramic USA

2.8.2 Dynamic Ceramic England

2.8.3 Azom.com, A to Z material

2.8.4 Cetek technologies Inc

2.9 Previous research related to current study

3 RESEARCH METHODOLOGY

3.1 Introduction

3.2 Project Methodology

3.3 Experimental Matrix

3.4 Experimental flow chart

3.5 Manual pallet press

3.6 Hot isostatic press (HIP) machine

3.7 Sintering furnace

3.8 Machinability testing

3.9 Ceramic powder

3.10 Measurement of the responses

3.10.1 Hardness measurement

3.10.2 Density measurement

3.10.3 Shrinkage and dimensional accuracy measurement

3.10.4 Machining responses

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4 RESULTS AND DISCUSSION

4.1 Introduction

4.2 Hardness

4.3 Density

4.4 Shrinkage

4.5 Surface roughness

4.6 Machinability

5 CONCLUSION

REFERENCES

APPENDICES 1 - 22

x

LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Properties of various ceramics at room temperature

2.2 Detail about alumina powder

2.3 Detail about zirconia powder

2.4 Show some previous study that related to current study

3.1 Selected process parameter and numbers of levels

3.2 Experiment planning

3.3 Detailed specification of Hot isostatic press (HIP) machine

3.4 Specification of HAAS SL20 lathe machine

LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1 Fundamental route to full density powder

2.2 Example of ball mill machine

2.3 Isostatic vs uniaxial

2.4 Isostatic shape change

2.5 Hot isostatic press machine

2.6 Example of Hot isostatic press process – diffusion bonding

2.7 Material comparison chart from Kyocera

3.1 Process flow chart

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3.2 Powder compaction process

3.3 Manual pallet press process

3.4 Normal sintering process

3.5 Samples inside the normal sintering furnace chamber

3.6 HIP furnace

3.7 Samples inside HIP furnace chamber

3.8 Carver manual pallet press model no:4350

3.9 Carver pallet dies with 13mm diameter

3.10 HIP machine model AIP6-30H

3.11 Normal sintering furnace model HT 16/18

3.12 HAAS lathe machine model SL20

3.13 Automatic tool change at the SL20

3.14 Tool holder for the experiment

3.15 Sample fix to tool holder

3.16 Tool adjustment

3.17 Workpiece fixed inside the lathe machine

3.18 Pycometer ACCUPYC 1330 used for density measurement

3.19 Weighing equipment Precisa XB3100C

3.20 Tool maker microscope Mitutoyo is used to measure the tool wear

3.21 Sample on the tool maker microscope

4.1 Hardness with diffrent zirconia composition

4.2 Hardness with diffrent sintering process

4.3 Density with diffrent zirconia composition

4.4 Density with diffrent sintering process

4.5 Diameter shrinkage

4.6 Thickness shrinkage

4.7 Surface roughness with diffrent zirconia composition

4.8 Tool wear with normal sintering process sample

4.9 Tool wear with HIP sintering process sample

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LIST OF APPENDICES

APPENDIX NO. TITLE

1 Pictures of samples

2 Machining sample 1




6-17 Surface roughness machine print result sample 1 – 12

18 Dimension of sample after normal sintering and HIP.

19 Density testing result

20 Hardness testing result (HR)

21 Hardness testing result (HV)

22 Surface roughness result

1

CHAPTER 1

INTRODUCTION

1.1 General Background

The increasing demand for ceramic composites as cutting tools for

machining steel based alloys in machining industries nowadays, is mainly due to

the trend towards high speed machining, dry cutting and the need for tools with

complex geometry. Because of these reasons, the ceramic material for examples

alumina and zirconia which have well known as hard and brittle materials are being

developed as cutting tools to penetrate the tooling market with new features, such

as longer tool life, able to cut difficult to machine material such as hardened steel,

nickel alloys etc.

Hot isostatic press (HIP) is one of the pressing technique that available in

the manufacturing of ceramic inserts. HIP have a wide range of applications such,

as a repair work for casting product or fabrication of metal matrix composite (mmc)

and ceramic matrix composite (cmm), and HIP is also used as part of the sintering

process.

Alumina is one of the major ceramic material in ceramic matrix composite

(cmc) field. It is also popular because of it’s excellent thermal and electrical

insulator behavior. Annual world production of alumina is approximately 65

million tones, over 90% from it is used to produce aluminium metal. Other major

use of alumina is in refractory (furnace wall), polishing/abrasive (grinding wheel),

cutting tool inserts, water filter and mixer (ball mill jar and ball) applications.

Zirconia sometimes known as zirconium dioxide is one of the most popular

ceramic material that has been explored. Zirconia is very useful because of its

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stable condition. It is mostly use as refractory material, in insulation, abrasive,

enamels, ceramic glaze and thermal barrier coating in jet turbine and diesel engines.

The composite that will be produced by mixing this two ceramic material

(alumina and zirconia) is known as zirconia toughen alumina (ZTA). In cutting tool

industry, ZTA cutting insert has been introduced but the secret formulation to

produce this product from the manufacturers make, it’s quite intresting to be

investigated.

This project is undertaken with the aims to evaluate the effect of HIP and

vacuum sintering process on the physical behaviour of composite ceramic part of

alumina and zirconia with respect to shrinkage, hardness, density, surface

roughness and machinability.

1.2 Problem Statement

Developing ceramic insert through powder technology involves basic

processes such as mixing, compaction and sintering with various parameters such

as powder composition, pressing pressure, pressing time, sintering temperature and

grain size of the ceramic powders. These parameters significantly affect the

mechanical and physical properties of the ‘green’ or ‘as-pressed’ compact before

and after sintering process such as density, hardness, strengthness and dimensional

accuracy. This processes and parameters are usually kept as company secret by

most cutting insert manufacturers.

In this study, the effect of the zirconia contents in alumina matrix composite

(commercially known as zirconia toughened alumina (ZTA)), and sintering process,

parameters on shrinkage, hardness, surface roughness, densification behaviour and

machining performance of the cutting insert were examined. Eventually the results

obtained will be used to design and produce an acceptable mold and to determine

the suitable content of zirconia in alumina based cmc.

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1.3 Objectives

Three specific objectives have been defined for this study. they are:

1. To develop ceramic inserts of alumina with zirconia using HIP and vacuum

sintering processes.

2. To evaluate the effect of zirconia content on the various responses such as

densification, surface roughness, shrinkage and machining performance.

3. To carried a comparative study between HIP and conventional sintering

process.

1.4 Scope of the Project

The scopes of the project are as follows:

1. Ball milling, manual compaction, hot isostatic press (HIP) process and vacuum

sintering process were employed in fabricating the ceramic insert.

2. The material used for the compaction and sintering process were aluminium

oxide (Al2O3) and zirconia / zirconium oxide (ZrO2).

3. Independ variables were zirconia content and sintering process .

4. Output responses included shrinkage, hardness, density, surface roughness and

tool life performance.

1.5 Expected Results

The following results are expected from this study :

1. The relationship between the process parameters and the responses of alumina-

zirconia composite powder will be established.

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2. The acceptable process parameters for producing the appropriate responses of

alumina-zirconia composite powder will be determined.

3. The predicted results and repeatable shrinkage upon sintering will be used for

designing the insert mold, to achieve a near net shape product.

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CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

Figure 2.1 : Three fundamental routes to full-density powder compacts based on

densification using pressure at room temperature, simultaneous temperature and

pressure, or densification in sintering [3].

Basically, the fundamental concept, process and applications of ceramic

processing and ceramic characteristics are discussed. The Hot Isostatic Press (HIP),

vacuum sintering processes, ball mill process, manual pallet press process and its

details are also included in this chapter. Then the review further highlighted the

findings of other researchers related to HIP and sintering process, specifically on

the physical behaviors and machinability.

In this study, powder technology is a major technology that will be used to

produce the sample, and one of the main objective is to obtain high density ceramic

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part. If the classification of densification technique is resumed as in Figure 2.1, the

process that was used is categorized as hybrid densification for HIP process and

sintering base densification for vacuum sintering process.

Mechanical Properties

Compared to metals, ceramics have the following relative characteristics:

brittleness; high strength and hardness at elevated temperatures; high elastic

modulus; and low toughness, density, thermal expansion, and thermal and electrical

conductivity. However, because of the wide variety of ceramics material

composition and grain sizes, the mechanical and physical properties of ceramics

vary significantly [7].

Because of their sensitivity to flaws, defects, and surface or internal cracks,

the presence of different types and level of impurities, and different methods of

manufacturing, ceramics can have a wide range of properties. For Hot Isostatic

Press (HIP) processes, mechanical properties of ceramic depend on the percent of

zirconia content, pressing pressure, pressing temperature and pressing time process

parameters. The relationship between these process parameters will be studied to

determine the hardness and density of alumina-zirconia (ZTA) powder after

compaction and sintering processes [7].

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2.2 Ball milling

Figure 2.2 : Example of ball mill machine.

A ball mill, type of a grinder, is a cylindrical device used to grind (or mix)

materials like ores, chemicals, ceramic raw materials and paints. Ball mills rotate

around a horizontal axis, partially filled with the material to be ground plus the

grinding medium. Different materials are used for media, including ceramic balls,

flint pebbles and balls. Figure 2.2 shows an example of a ball mill machine.

An internal cascading effect reduces the material to a fine powder. Industrial

ball mills can operate continuously, fed at one end and discharged stainless steel at

the other. Large to medium ball mills are mechanically rotated on their axes, but

small ones normally consist of a cylindrical capped container that sits on two drive

shafts (pulleys and belts are used to transmit rotary motion). A rock tumbler

functions on the same principle. Ball mills are also used in pyrotechnics and the

making of black powder, but can't be used in the making of some pyrotechnic

mixtures such as flash powder because of their sensitivity to impact. High quality

ball mills are potentially expensive and can grind mixture particles to as small as

0.0001 mm, enormously increasing surface area and reaction rates[11].

There are many types of grinding media suitable for use in a ball mill, each

material having its own specific properties and advantages. Common in some

applications are stainless steel balls. While usually very effective due to their high

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density and low contamination of the material being processed, stainless steel balls

are unsuitable for some applications, including:

• Black powder and other flammable materials require non-sparking

lead antimony, brass, or bronze grinding media

• Contamination by iron of sensitive substances such as ceramic raw

materials. In this application ceramic or flint grinding media is used.

Ceramic media are also very resistant to corrosive materials.

2.3 Hot Isostatic Press (HIP)

Hot Isostatic Pressing (HIP) is an innovative thermal treatment carried out

in a pressure vessel under high isostatic pressure and temperature, in order to

eliminate porosity, particularly in castings, prior to finish machining, densify metal

and ceramic powders, consolidate powder-metallurgy parts.

Applications of HIP include, castings, titanium alloy steel, aluminium,

magnesium, ceramics, diamond tools, gallium arsenide mirrors, glass, medical

implants, sputtering targets and infra-red windows.

The HIP process (Figure 2.3 and 2.4) subjects a component to both elevated

temperature and isostatic gas pressure in HIP chamber. The pressurizing gas most

widely used is argon. An inert gas is used, so that the material does not chemically

react. The chamber is heated, causing the pressure inside the chamber to increase.

Due to the presence of the gas, pressure is applied to the material from all directions

(hence the term "isostatic"). Figure 2.5 show the schematic illustration between HIP

and conventional axial processing. The isostatic shape change and the HIP machine

are shown in Figure 2.5 and 2.6 respectively [6].

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Figure2.3 : Hot Isostatic Press machine

Figure 2.4: Example of Hot Isostatic Press process – diffusion bonding

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Figure 2.5 : Isostatic vs Uniaxial

Figure 2.6: Isostatic shape change

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2.4 Ceramics material.

Ceramics are inorganic, nonmetallic materials which consist of metallic and

nonmetallic elements bonded together primarily by ionic or covalent bonds. The

term ceramics (from the Greek words keramos meaning potter’s clay and

keramikos meaning clay products) refer both to the material and to the ceramic

product itself. There are three basic categories of ceramics [7] :

1. Traditional ceramics: Silicates used for clay products such as pottery and bricks,

common abrasives and cement.

2. New ceramics: More recently developed ceramics based on nonsilicates such as

oxides and carbides and generally possessing mechanical or physical properties

that are superior or unique compared to traditional ceramics.

3. Glasses: Based primarily on silica and distinguished from the other ceramics by

their noncrystalline structure.

Ceramic can also be classified as technical ceramics (engineering ceramics).

Silicon carbide, silicon nitride, sialons and zirconium dioxide are among the

engineering ceramics. These relatively new ceramic materials have high

strength, high temperature resistance, high wear resistance and good corrosion

resistance. These materials are therefore used in various mechanical devices,

such as sealing rings, engine parts, ball bearings and cutting tools. Technical

ceramics can be further classified into three distinct material categories [7]:

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1. Oxides: Alumina, zirconia.

2. Non-oxides: Carbides, borides, nitrides and silicides.

3. Composites: Particulate reinforced, combinations of oxides and non-oxides [7].

2.4.1 Properties of Ceramics

The mechanical, thermal, optical and electrical properties of ceramics are a

product of their structure, processes employed to manufacture them and their

chemical composition. In general ceramics are hard, brittle, strong materials that

are poor conductors of heat and electricity and are chemically inert. Physical

properties of various ceramics at room temperature are shown in Table 2.1.

Some of the properties are as follows [6] :

1. Density: In general ceramics are lighter than metals and heavier than polymers.

2. Melting temperature: Higher than most metals (some ceramics decompose

rather than melt).

3. Electrical and thermal conductivities: Lower than most metals but the range of

values is greater so some ceramics are insulators while others are conductors.

4. Thermal expansion: Some are less than metals but effects are more damaging

because of brittleness.

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Many of these properties are developed as the ceramics give up moisture

through regulated drying and sintering processes. The rate and temperature are

important to the development of strength properties. The strength properties of

ceramics are highlighted as follows [3]:

1. Theoretically the strength of ceramics should be higher than metals because

their covalent and ionic bonding types are stronger than metallic bonding.

2. However metallic bonding allows for slip which in the basic mechanism by

which metals deform plastically when subjected to high stresses.

3. Bonding in ceramics is more rigid and does not permit slip under stress.

4. The inability to slip makes it much more difficult for ceramics to absorb

stresses.

There are some fimiliar methods to strengthen the ceramic materials [5]:

1. Ensuring the uniformity of the starting materials.

2. Decrease grain size in polycrystalline ceramic product.

3. Minimize porosity.

4. Introduce compressive surface stresses.

5. Use fiber reinforcement.

6. Heat treatment.

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Figure 2.7 show the various properties of ceramic materials [10].

Table 2.1: Properties of various ceramics at room temperature

Material

Symbol

Compressive

Strength

(Mpa)

Elastic

Modulus

(GPa)

Hardness

(HK)

Density

(kg/m3)

Alumina Oxide

Al2O3

1000-2900

310-410

2000-3000

4000-4500

Cubic boron nitride

CBN

7000

850

4000-5000

3480

Silicon nitride

Si3N4

No data

300-310

2000-2500

3300

Silicon carbide

SiC

700-3500

240-480

2100-3000

3100

Titanium carbide

TiC

3100-3850

310-410

1800-3200

5500-5800

Tungsten carbide

WC

4100-5900

520-700

1800-2400

10000-15000

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Figure 2.7 : Material comparison chart from Kyocera [10].

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2.5 Alumina Powder

Alumina is a chemical compound of aluminum and oxygen with the

chemical formula Al2O3 and generally available in two concentrations: 99.5% and

96%. Alumina oxide is responsible for metallic aluminum’s resistance to

weathering. Metallic aluminum is very reactive with atmospheric oxygen and a thin

passivation layer of alumina oxide quickly forms on any exposed aluminum

surface. This layer protects the metal from further oxidation. The thickness and

properties of this oxide layer can be enhanced using a process called anodizing. A

number of alloys, such as aluminum bronzes, exploit this property by including a

proportion of aluminum in alloy to enhance corrosion resistance[12].

Alumina is produced on an industrial scale using the Bayer Process to

separate ferric oxide, silica and aluminum oxides. Bauxite ore is ground finely then

treated with sodium hydroxide (NaOH) in an iron autoclave at an elevated

temperature. The alumina dissolves as sodium aluminate via the equation: Al2O3 +

2NaOH at 2NaAlO2 _ H2O. The silica dissolves to form sodium silicate but the

ferric oxide, being insoluble, is filtered off. Carbon dioxide is then passed through

the solution, decomposing the sodium aluminate (Al02) to form aluminum

hydroxide and sodium carbonate: 2NaAlO + CO,- Na, CO, + 2Al (OH)[12].

The aluminum hydroxide is separated by filtration and calcined at 1000 °C

or higher, when it loses its water of constitution, yielding alumina: 2Al(OH)3 at

Al2O3 + 3 H2O. Pure crystalline alumina is a very inert substance and resists most

aqueous acids and alkalis. It is more practical to use either alkaline (NaOH) or

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acidic (KHS04, KHF2, etc) melts. Concentrated boiling sulfuric acid also can be

used as an etchant [5].

In order to produce usefull parts, alumina must be densified or sintered.

Sintering is the process in which a compact of a crystalline powder is heat treated to

form a single coherent solid. The driving force for sintering is the reduction in the

free surface energy of the system. This is accomplished by a combination of two

processes, the conversion of small particles into fewer larger ones (particle and

grain growth) and coarsening, or the replacement of the gas or solid interface by a

lower energy solid or solid interface (densification). This process is modeled in

three stages:

1. Initial: The individual particles are bonded together by the growth of necks

between the particles and a grain boundary forms at the junction of the two

particles.

2. Intermediate: Characterized by interconnected networks of particles and pores.

3. Final: The structure consists of space-filling polyhedra and isolated pores.

Alumina products include abrasives, insulators, structural members,

refractory bricks, electronic substrates, and tools. Alumina is stable, hard,

lightweight, and wear resistant, making it attractive for such applications as seal

rings, air bearings, electrical insulators, valves, thread guides, as well as the

ceramic reinforcing component in metal matrix composites[9].

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2.5.1 Properties of Alumina Powder

Alumina powder offers a combination of good mechanical and electrical

properties leading to a wide range of applications. Alumina can be produced in a

range of purities with additives designed to enhance properties. It can be formed

using a wide variety of ceramic processing methods and can be machined or net

shaped formed to produce a wide variety of sizes and shapes of component. In

addition it can be readily joined to metals or other ceramics using metallising

and brazing techniques. Table 2.2 show the properties of alumina powder.

Table 2.2: Properties of alumina powder [8]

Aluminium oxide

General

Other names Alumina

Molecular formula Al2O3

Molar mass 101.96 g/mol

CAS number [1344-28-1]

Properties

Density and phase 3.97 g/cm3, solid

Solubility in water Insoluble

Melting point 2054 oC

Boiling point ~3000 oC

Thermal conductivity 18 W/m.K

Structure

Crystal structure Rhombohedral, Cubic, Tetragonal, Monoclinic, Hexagonal, Orthorhombic

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2.6 Zirconia powder.

Zirconium dioxide (ZrO2), sometimes known as zirconia, is a white

crystalline oxide of zirconium. Its most naturally occurring form, with a monoclinic

crystalline structure, is the rare mineral, baddeleyite. The high temperature cubic

crystalline form, called 'cubic zirconia', is rarely, if ever, found in nature, but is

synthesized in various colours for use as a gemstone. The cubic crystal structured

variety is the most well known diamond simulant.

Zirconium dioxide is one of the most studied ceramic materials. Pure ZrO2

has a monoclinic crystal structure at room temperature and transitions to tetragonal

and cubic at increasing temperatures. The volume expansion caused by the cubic to

tetragonal to monoclinic transformation induces very large stresses, and will cause

pure ZrO2 to crack upon cooling from high temperatures. Several different oxides

are added to zirconia to stabilize the tetragonal and/or cubic phases: magnesium

oxide (MgO), yttrium oxide, (Y2O3), calcium oxide (CaO), and cerium oxide

(Ce2O3), amongst others.

Zirconia is very useful in its 'stabilized' state. In some cases, the tetragonal

phase can be metastable. If sufficient quantities of the metastable tetragonal phase

is present, then an applied stress, magnified by the stress concentration at a crack

tip, can cause the tetragonal phase to convert to monoclinic, with the associated

volume expansion. This phase transformation can then put the crack into

compression, retarding its growth, and enhancing the fracture toughness. This

mechanism is known as transformation toughening, and significantly extends the

reliability and lifetime of products made with stabilized zirconia. A special case of

zirconia is that of tetragonal zirconia polycrystaline or TZP, which is indicative of

polycrystalline zirconia composed of only the metastable tetragonal phase.

The cubic phase of zirconia also has a very low thermal conductivity, which

has led to its use as a thermal barrier coating or TBC in jet turbine and diesel

engines to allow operation at higher temperatures. Thermodynamically the higher

the operation temperature of an engine, the greater the possible efficiency. As of

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2004, a great deal of research is ongoing to improve the quality and durability of

these coatings.[9]

Zirconia is one of few compounds that actually becomes conductive at high

temperatures, and more conductive, as its temperature increases. Zirconia starts out

with a very high resistance at room temperature, greater than 1 trillion ohm-cm. As

the temperature increases it has less than 20,000 ohm-cm at 500 degrees Celsius, to

having less than 1,000 ohm-cm of resistance at 1,000 degrees Celsius. It loses

nearly all of its resistance around 2,000 degrees Celsius, and becomes a very good

conductor.

Zirconium dioxide also occurs as a white powder and possesses both acidic

and basic properties. On account of its infusibility, and brilliant luminosity when

incandescent, it was used as an ingredient of sticks for limelight.

Zirconia is also an important dielectric material that is being investigated for

potential applications as insulators in transistors in future nanoelectronic devices

Single crystals of the cubic phase of zirconia are commonly used as a

substitute for diamond in jewellery. Like diamond, cubic zirconia has a cubic

crystal structure and a high index of refraction. Discerning a good quality cubic

zirconia gem from a diamond is difficult, and most jewellers will have a thermal

conductivity tester to identify cubic zircona by its low thermal conductivity

(diamond is a very good thermal conductor). This state of zirconia is commonly

called "cubic zirconium" or "zircon" by jewellers, but these names are not

chemically accurate. Zirconium silicate (ZrSiO4), is the naturally occurring silicate

mineral zircon. Its transparent form is also used as a gemstone, and its opaque form

as a refractory

The detail properties of zirconia powder is given in Table 2.3.

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Table 2.3: Detailed about zirconia powder [8].

Zirconium Dioxide

General

Other names Zirconia

Molecular formula ZrO2

Molar mass 91.224 g/mol

CAS number [7440-67-7]

Properties

Density and phase 6.52 g/cm3, solid

Solubility in water Insoluble

Melting point 1855 oC

Boiling point ~4409 oC

Thermal conductivity 22.6 W/m.K

Structure

Crystal structure Hexagonal

2.7 Zirconia Toughened Alumina (ZTA) cutting tools

Zirconia Toughened Alumina (ZTA) shows considerable improvement in

strength and toughness, this is brought about through the stress induced

transformation toughening mechanism.

ZTA is strengthened by fine zirconia particles uniformly dispersed

throughout the alumina body. Typical zirconia content is between 10% and 20%. It

has an excellent mechanical properties like :

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2

- Wear resistance

- High temperature stability

- Corrosion resistance

2.8 Commercial ZTA product.

There are many commercial ZTA product in the market. Some of these

product are shown in appendix 1.

2.9 Previous research related to current study

There are various studies related to the current project. These are shown in

Table 2.4.

Table 2.4 show some previous study that related to current study.

No. Researcers Topic Finding

1. Sarizal Md Ani,

Mechanical Engineering

Faculty, UTM, Malaysia.

(2006)

Physical behaviour

of powder ceramic

part using Cold

Isostatic Pressing

(CIP) process

Produce alumina samples

with CIP compaction

process and normal

sintering process.

He found that the hardness

increase was very small

amount within 1.0% to

1.5% for each different

pressurization and timing.

Average hardness value at

sintering temperature

13000C, 15000C and

17000C were 68.3

22

2

(HR15N), 85.3 (HR15N)

and 91.2 (HR15N)

respectively.

Increasing pressing pressure

– will increase green

density of alumina linearly

about 2.5%.

Increasing pressing pressure

of the CIP resulted is an

increase of sintered density,

however the increasing was

very marginal

2 Sung R. Choi Ohio

Aerospace Institute,

Brook Park, Ohio

Narottam P. Bansal

Glenn Research Center,

Cleveland, Ohio (2003).

Alumina-

Reinforced

Zirconia

Composites

Alumina-reinforced zirconia

composites was fabricated

by hot pressing 10 mol%

yttria-stabilized zirconia

(10-YSZ) reinforced with

two different forms of

alumina—particulates and

platelets—each containing 0

to 30 mol% alumina.

At ambient temperature,

both flexure strength and

fracture toughness increased

with increasing alumina

content, reaching a

maximum at 30 mol%.

Vickers microhardness of

the particulate composites

increased with increasing

23

2

alumina content; while

Vickers microhardness of

the platelet composites

followed an opposite trend,

in which a significant

decrease in hardness

resulted in higher alumina

contents

3 B. Smuk, M.

Szutkowska, J. Walter

Materials Engineering

Department, The Institute

of Metal Cutting, ul.

Wrocławska 37a, 30-011

Krakow, Poland. (2003).

Alumina ceramics

with partially

stabilized zirconia

for cutting tools

A series of ceramic tool

materials based on Al2O3

with ZrO2.

The alumina ceramics

obtained with the addition

of 20 mass% of the zirconia

stabilized (ZY5) and

sintered at 1615 oC for 60

min are characterized by the

best mechanical properties

from among the tested

compound compositions.

This type of alumina

ceramics gives greater wear

resistance, TRS (even about

80%), tool life of the cutting

edge and better toughness at

the same hardness, in

comparison with pure

Al2O3 ceramics.

Preliminary industrial tests

confirm the high cutting

24

2

performance of alumina

ceramic cutting inserts,

which will allow practical

application in industrial

conditions for the

moderately accurate and

rough tourning of cast iron

and carbon steel.

4 O. Van der Biest and J.

Vleugels Department of

Metallurgy and Materials

Engineering, Katholieke

Universiteit Leuven,

Kasteelpark Arenberg,

44, B-3001 Heverlee,

Belgium (2002).

Perspectives on the

Development of

Ceramic

Composites or

Cutting Tool

Applications

In this paper the

requirements for ceramic

composites as cutting tools

for machining iron based

alloys are reviewed, taking

into account the trends in

the industry towards dry

high speed cutting and the

need for tools with complex

geometry.

It is concluded that alumina

and zirconia are promising

matrices for composites to

machine steel.

5 Giuseppe Magnania,,

Aldo Brillanteb, ENEA,

Bologna Research

Center, Via dei Colli,

40136 Bologna, Italy,

University of Bologna,

Effect of the

composition and

sintering process on

mechanical

properties and

residual stresses in

Zirconia-toughened alumina

(ZTA) with small amounts

of chromia and

magnetoplumbite-type

crystalline phase

(CeMgAl11O19) have been

prepared and processed

under different conditions.

25

2

Department of Physical

and Inorganic Chemistry,

40136 Bologna, Italy

(2005).

zirconia–alumina

composites

Main results are:

The highest value of

fracture toughness was

achieved with pressureless

sintering of the composite

containing chromia 0.5

wt.% and yttria 2 mol%.

Post-hot isostatic pressing

treatment caused the

formation of a small

quantity of monoclinic

phase that reduced fracture

toughness.

Transformability was

strongly affected by

stabilizer content.

Chromia addition led to an

enhancement of the fracture

toughness.

Stress-induced

transformation toughening

is the mechanism

responsible for the fracture

toughness improvement.

6 Shunzo Tashima, Yasuo

Yamane, Hidenori

Kuroki and Norihiko

Narutaki Cluster & Fat.

Eng. Hiroshima

University, 1-4-l

Cutting

Performance of

High Purity

Alumina Ceramic

Tools formed by a

High-speed

In this study by using a

high-speed centrifugal

compaction process, a slip

prepared from alumina

powder with a purity of

99.99 % and an average

particle size of 0.22 D m

26

2

figamiyama, Higashi-

hiroshima 739 Japan

(1996)

Centrifugal

Compaction

Process

was compacted, and

sintered at 1230 “C for 1.5

hours in the atmosphere.

The sintered compact has

superior mechanical

properties, including a 3 –

point bending strength of

1330 MPa and a Vickers

hardness of 2100

The results show that tools

manufactured using the

subject high - speed

centrifugal compaction

process have relatively high

wear resistance and fracture

resistance as compared with

commercially available high

purity alumina ceramic

tools.

7 A. Senthil Kumar , A.

Raja Durai , T.

Sornakumar

,Manufacturing

Engineering Division,

Department of

Mechanical Engineering,

Anna University,

Chennai 600025, Indiab

Machinability of

hardened steel

using alumina

based ceramic

cutting tools

In this paper the

machinability of hardened

steel using alumina based

ceramic cutting tool

materials is analysed.

Abrasive wear is found to

be the predominant wear

mechanism in alumina

based ceramic cutting tool

materials when machining

hardened steel.

Zirconia toughened alumina

27

2

Department of


Thiagarajar College of

Engineering, Madurai

625015, India (2003).

ceramic tool is not affected

by diffusion wear. Surface

finish improves with

increasing cutting speed for

both types of ceramic

cutting tool materials.

8 D. Sarkar, S. Adak ,

N.K. Mitra, Department

of Ceramic Engineering,

National Institute of

Technology, Rourkela

769008, Orissa, India,

Department of Chemical

Technology, University

of Calcutta, 92, A.P.C.

Road, Kolkata 9, India

(2006)

Preparation and

characterization of

an Al2O3–ZrO2

nanocomposite,

Part I: Powder

synthesis and

transformation

behavior during

fracture

In this study the fine ZrO2

(100–300 nm) has been

homogeneously dispersed

within the alumina matrix

with a maximum grain size

of _0.8 lm, which will

increase the toughness of

the alumina matrix.

9 Bikramjit Basu, Jozef

Vleugels, Omer Van Der

Biest, Ceramics

Laboratory, Department

of Materials and

Metallurgical

Engineering, Indian

Institute of Technology,

Kanpur, India,

Department of

Metallurgy and Materials

Engineering, Katholieke

Universiteit Leuven,

ZrO2–Al2O3

composites with

tailored toughness

In this paper their found that

the toughness of Y-TZP

based composites with 20

wt.% Al2O3 can be

increased by careful

engineering of the ZrO2

matrix by means of the

“mixing route”.

The optimum toughness,

pursued in this route, is

much higher than that of the

commercial co-precipitated

powder based ceramics,

28

2

Kasteelpark Arenberg

44, B-3001 Leuven,

Belgium (2004)

sintered under the same

experimental conditions.

The hardness is

considerably enhanced in

the Y-TZP/Al2O3 (72/28)

composites while

maintaining the excellent

toughness of the zirconia

matrix.

10 B.H. Yan , F.Y. Huang a,

H.M. Chow, Department

of Mechanical

Engineerin9, National

Central University,

Chuno-Li, Taiwan, ROC

Department of


Nan Kai Institute, Nan-

Tou, Taiwan, ROC

(1995).

Study on the

turning

characteristics of

alumina-based

ceramics

It is found that PCD tool is

superior to the other tools,

whilst the carbide tool and

the ceramic tool are

unsuitable for machining

ceramics materials. It is

found that, despite their

brittle nature, cutting fine-

sintered ceramics with a

PCD tool at the optimum

cutting conditions of cutting

speed v = 60m/min, feed

rate f= 0.029 mm/rev and

cutting depth d = 0.015 mm,

resuits in the formation of a

continuous chip under a

plastic- deformation

mechanism, as for metal

cutting, and the best surface

finish is obtained. It is also

found that turning ceramics

with a sucker in cool and

29

3

highly humid weather

moistens the tool face and

promotes tool wear.

However, when turning

with hot blowing and

sucking, the tool wear has

considerable improvement,

due to improvement in chip

discharge.

11 A. Senthil Kumara, A.

Raja Durai, T.

Sornakumar, Department

of Production

Engineering, Sethu

Institute of Technology,

Madurai 626106, India

(2006).

The effect of tool

wear on tool life of

alumina-based

ceramic cutting

tools while

machining

hardened

martensitic

stainless steel

Zirconia toughened alumina

ceramic cutting tool is

affected by the flank wear at

lower speed but it is

affected by notch wear at

higher speed.

Machining tests have been

carried out in a precision

lathe, using these alumina-

based ceramic cutting tools

at cuttingspeeds of 120, 170,

220 and 270 m/min at a

constant feed rate of 0.12

mm/rev and at a constant

depth of cut of 0.5 mm,

without any cutting fluid.

Flank wear, crater wear and

notch wear were measured

30

3

using tool room microscope

and micro stylus attached

dial gauge.

31

3

CHAPTER 3

RESEARCH METHODOLOGY

3.1 Introduction

In this chapter the methodology used in conducting the experiment are

discussed in detail. Brief explanation on the experiment procedures was highlighted

which include the types and specification of the equipments and machines, features

of alumina and zirconia powder and the insert mold.

3.2 Experimental procedures

The following steps outlined the procedures involved in design,

implementation and analyzing the experiments for this project:

Step 1: Identify the potential factors or parameters for the study (zirconia content,

pressing pressure, pressing time, HIP temperature, vacuum sintering temperature

and cutting speed).

Step 2: Select the number of factors involved in the experiment.

Step 3: Multiply all factors involved and determine the number of experiment to be

carried out.

Step 4: Run the experiments as designed (ball mill,compaction and sintering).

Step 5: Analyze the experimental results with respect to the objective of the study.

Step 6: Discuss the results and make conclusion.

32

3

3.3 Experimental Matrix

The process parameters considered during the experiment is shown in Table

3.1.

Table 3.1: Selected process parameters and numbers of levels

Process parameter

Level

Numbers of level

1) Zirconia content

10%, and 20%

2

2) Sintering process

Normal sintering (1700oC)

HIP sintering (1700oC +200Mpa)

2

3) Cutting speed m/min

100, 130 and 150

3

A total of 12 ( 2 x 3 x 2 ) experiments were conducted. Zirconia contents,

sintering process and cutting speed were the parameters that were be used in this

experiments. The detail experimental of plan is shown in Tables 3.2 .

33

3

Table 3.2 : Experiment planning

Code

Zirconia Content

Sintering Process

Sample 1 Z-10-N1 10% Normal



Sample 4 Z-10-H1 10% HIP









Machining Parameters

Cutting Speed : V = 150 Feed Rate : 0.12mm/rev Depth of Cut : 0.5mm

Condition : Dry Cutting

34

3

3.4 Experimental Flow Chart

Figure 3.1 : Process Flow Chart

ALUMINA + ZIRCONIA

20% ZIRCONIA 6 samples

10% ZIRCONIA 6 samples

BALL MILL PROCESS

MANUAL PELLET PRESS WITH INSERT MOLD 200 Mpa - 30 sec

2 compositions x 6 samples = 12 samples

HOT ISOSTATIC PRESS 1700oC + 200Mpa

NORMAL SINTERING 1700oC

- Hardness - Density - Surface Roughness - Shrinkage - Machinability

- Hardness - Density - Surface Roughness - Shrinkage - Machinability

35

3

In this study the hardness, densification and machinability behavior of

alumina zirconia composite insert were investigated using the two different

sintering processes (conventional and HIP). Analyses were done on the shrinkage,

roundness and surface roughness of the ceramic parts. The powders used in this

experiments were pure 99% alumina and 95% zirconia + 5% yittria .

Alumina and zirconia powders were mixed into two different compositions,

which was 10% Zirconia + 90% Alumina and 20% Zirconia + 80% Alumina. The

mixing process used ball mill process, which operated at 250 RPM and the ball to

powder weight ratio was 10:1.

After ball milling and mixing process the composite powders were

compacted with a manual pallet press using a round pallet mould with diameter

13mm to produce ZTA the green samples. The thickness of the sample was

maintained at 4mm ± 0.2mm. The pressure was also maintain at 200 Mpa. The

calculation for the pressure is stated below.

F= P/A

1kg/cm2 = 0.098 Mpa

1 metric tons = 1000kg

1000kg/cm2 = 98Mpa

Mold diameter = 1.3cm

Mold surface area = ∏D2/4 = 1.327 cm2

1 metric tons / 1.327 cm2 = 98/1.327 Mpa = 73 Mpa

200 Mpa / 73 Mpa = 2.74 metric tons

To obtain 200 Mpa pressure to 1.3cm diameter insert mold, 2.74 metric

tons force must be applied during compaction with manual pallet press

process.

The powder preparation process is shown in Figure 3.2 and the manual pallet press

is shown in Figure 3.3.

36

3

Figure 3.2 : Powder preparation process

Figure 3.3 : Manual pallet press process

37

3

After the compaction process, the samples were measured dimensionally

and weighed. This is to determined the ‘green density’ and ‘green shrinkage’ of

each sample. A digital vernier caliper and electronic densimeter were used to

measured the dimensional features and mass of the sample respectively. The

samples were then dried naturally for 24 hours.

After the samples were dried, sintering process was carried out, 12 samples,

with different composition were sintered, 6 samples with normal sintering and

another 6 samples were sintered with HIP. For normal sintering the specimens were

heated and rammed up to 1700oC at 100C/min with 5 hours holding time, after that

the samples were cooled down to 40oC before the furnace was opened and the

samples were gradually cooled to room temperature. Figure 3.4 and 3.5 shown the

normal sintering process were carried out.

Figure 3.4 : Normal sintering process

38

3

Figure 3.5 : Samples inside the normal sintering furnace chamber.

In the HIP, all the 6 samples were heated to 1700oC at 5oC/min, with the

applied pressure of 200 Mpa. The holding time was set to 2 hours, before cooling

down to 40oC. The furnace was opened and the samples were cooled gradually to

room temperature.

Figure 3.6 and 3.7 shown the HIP furnace and the samples inside the

furnace chamber.

39

4

Figure 3.6 : HIP furnace

Figure 3.7 : Samples inside HIP furnace chamber

40

4

After the sintering process, all samples were measured and weighed. The

effect of sintering temperature on the dimension (size) determined the shrinkage of

the sample after sintered. Coordinate Measuring Machine (CMM) was used to

measure the dimensional tolerances of the samples. Meanwhile the weight loss after

sintering was measured using an electronic densimeter.

According to Boyle–Mariotte's law of volume-pressure relationship (gas

pycnometer), the density of the samples were measured using the Micromeritics

apparatus. The density of sintered sample was calculated using the following

equations:

ρ = msintered / vsample

where msintered is the mass of sample after sintered and

exp

1

2

1sample cell

g

g

vv v p

p

= −−

After sintering, the hardness of the samples were then measured using a

Rockwell Hardness Tester (HR15N). Finally, the effect of sintering temperature on

the dimension accuracy and the surface roughness of the samples were determined

using the Surface Roughness Tester respectively.

Finally machining test (turning) was carried out the fabricated samples

using CNC HAAS SL20 lathe machine, the tool holder was PCLN which was

manufactured by KENNAMETAL, machining condition were set as follows:

Feed rate = 0.12 mm/rev

Depth of cut = 0.5 mm

Coolant = Dry cutting

Cutting speed = 150 m/min

Workpiece material = Hardened steel

41

4

3.5 Manual pallet press

Manual pellet presses are designed to compact homogeneous powder into a

usable pellet sample. Pellet dies are constructed of stainless steel for corrosion

resistance with replaceable anvils. All dies come with a pellet ejector. In this study

Carver pellet press model no:4350 was used to produce the samples. A 13 mm

diameter die for sample preparation was supplied with a 12 ton press.

Figure 3.8: Carver Manual Pallet Press model no: 4350

42

4

Figure 3.9: Carver Pallet Dies with 13mm diameter.

3.6 Hot Isostatic Press (HIP) Machine

HIP process is widely used to manufacture near net shape components. In

this study a HIP machine model AIP6-30H manufactured by American Isostatic

Presses Inc. was used. The machine features a forged monolithic steel pressure

vessel with a fully threaded top enclosure. Maximum operating pressure for the

machine is 200 MPa, with a maximum pressing time of 24 hours. Figure 3.3 and

Table 3.3 showed the CIP machine and the detail specifications respectively.

43

4

Figure 3.10: HIP machine model AIP6-30H

Table 3.3: Detailed specification of Hot isostatic press (HIP) machine.

Specifications: Model AIP6-30H

Maximum working

temperature

1700OC under vacuum

1800OC below 500 PSI

2200OC 500 PSI to 30000 PSI ( 200 Mpa )

Working hot zone 3.25’’ diameter X 5.0’’ long

Steady state power

consumtion

8.50 KW @ 1800OC and 30000 PSI

Furnace weight 20 pounds ( 454 g )

Maximum workload

weight

20 pounds ( 454 g )

Maximum air exposure

temperature

200oC

44

4

3.7 Sintering Furnace

In this study, sintering furnace model HT 16/18 (Figure 3.4) from

Nabertherm GmbH was used. Maximum temperature of 18000C can be

accommodated the 16 liter capacity. Molybdenum disilicate (MoSi2) was used as

heating elements. The furnace was equiped with a C 40 controller and a LCD

display for program depiction and continuous display of the actual temperature with

18 segments for each program.

Figure 3.11: Normal sintering furnace model HT 16/18 from Nabertherm GmbH

3.8 Machinability testing

Machinability testing was conducted on a HAAS CNC lathe machine,

Model SL20 (Figure 3.5), with specification shown in Table 3.4. The automatic tool

change is shown in Figure 3.6. The tool holder supplied by KENNAMETAL is

shown in Figure 3.7

45

4

Table 3.4 : Specification of HAAS SL20 lathe machine

Capacity Spindle

Chuck size 8.3” Peak horsepower 20hp

Bar capacity max 2.0” Max RPM 4000rpm

Between centres 24.0” Spindle nose A2-6

Max cutting dia. 10.0” Bore dia. 3.0”

Max cutting length 20.0” Draw tube bore dia 2.06”

Figure 3.12 : HAAS lathe machine model SL20

46

4

Figure 3.13 : Automatic tool change at the SL20

Figure 3.14: Tool holder for the experiment.

47

4

Figure 3.15 : Sample fix to tool holder

Figure 3.16 : Tool adjustment

48

4

Figure 3.17 : Workpiece mounted inside the lathe machine

3.10 Ceramic powder

Ceramic powder that was be used in this experiment is alumina with 99.7%

purity, 0.3% silicate and magnesium (bonded material), with mean particles size of

0.6μm.

The zirconia specification is zirconia, PSZ yttria 94.8% Zr(Hf)O2, 5.2%

Y2O2 (Yittrium oxide), with particles size of 0.03μm.

49

5

3.11 Measurement of the Responses

Seven responses were investigated for the sample after the compaction and

sintering process which include green shrinkage, sintered shrinkage, hardness,

green density, sintered density, and surface roughness. Meanwhile responses such

as hardness, sintered density, sintered shrinkage, roundness, surface roughness and

machinability were carried out after sintering process.

3.11.1 Hardness Measurement

The hardness of the samples after sintering was determined using a

Mitutoyo Digital Rockwell Hardness Tester, ATK-F3000. Scale symbol of 15N

was used with spheroconical diamond indenter. By using HR15N testing,

preliminary force was 29.42 N and total force was 147.1 N. This tester conformed

to ASTM E-18 Superficial Rockwell Hardness Standard and suitable for the

measurement of ceramic parts.

3.11.2 Density Measurement

Density after sintering was measured by using the Micromeritics gas

pycnometer, AccuPyc 1330 (Figure 3.18). This is a general purpose type with

resolution of 0.0001 g/cm3 and measurable volume depended on the size of cup.

The AccuPyc 1330 pycnometer is a gas displacement pycnometer, a type of

instrument which measures the volume of solid object of irregular or regular shape

whether powdered or solid. The gas pycnometer uses the law of ideal gas to

determine the volume of the sample, given a known volume of the sample chamber,

gas reservoir and a change in pressure. The volume of the sample is translated into

the absolute density, as the weight of the sample is known. For measured ‘green

50

5

density’ the volume of sample was calculated after compaction using the density

equation.

Figure 3.18 : Pycometer AccuPyc 1330 used for density measurement

Figure 3.19 : Weighing equipment Precisa XB3100C for weighing process.

51

5

3.11.3 Shrinkage and dimensional accuracy measurement

The samples after compaction (green bodies) and samples after sintering

were measured by using a Mitutoyo digital, C20-M230 and a Mitutoyo Coordinate

Measuring Machine (CMM), Beyond Apex A504. A digital caliper was used to

measured the thickness and diameter of the sample after compaction. This data was

used to calculate the ‘green shrinkage’ after compaction.

Meanwhile CMM and Geopack software were used to measure the sample

after sintered. A PH-9A probe with a stylus diameter of 2 mm was used for

measuring the diameter and thickness of the sample.

3.11.4 Machining responses

Machinability testing was carried out and the tool wear was measured after

two minutes of cutting time for every samples and every cutting speed. A tool

maker microscope from Mitutoyo was used to measure the flank wear of the tool.

52

5

Figure 3.20 : Tool maker microscope Mitutoyo to measure the tool wear

53

5

Chapter 4

Results and Discussion

4.1 Introduction

In this chapter, results from the experiments were compared and analyzed

accordingly. The process parameters were sintering process and zirconia content

(10% and 20%) in alumina based ceramic composite. The responses evaluated were

hardness, density, shrinkage, surface roughness and machinability.

4.2 Hardness

In general, hardness decreases with increase in zirconia content for both

normal and HIP sintering process. Hardness values decrease about 5% for normal

sintering and 0.8% for HIP with zirconia content from 10% to 20% (Figure 4.1).

Theoretically this is true because of the alumina have a higher hardness than

zirconia.

Figure 4.2 shows that the hardness of 10% zirconia sample was always

higher than 20% zirconia samples regardless of the sintering process. Range of

hardness for 10% zirconium samples was 87 – 90 (HR15N) where range of

hardness for 20% zirconium sample was 85 – 87 (HR15N).

For sample with different sintering process, that is from normal to HIP,

results indicated that the hardness values opposed the theoretical value.

54

5

This maybe deu to the purity of ceramic powder, temperature error, etc,

however the different was marginal as shown in Figure 4.2.

Figure 4.1 : Hardness with different zirconia composition

Figure 4.2 : Hardness with different sintering process

Hardness With Different Zirconia Composition

838485868788899091

10% Zr 20% Zr

Zirconia Composition

Hard

ness

(HR

15N)

Normal SinteringHIP Sintering

Hardness With Different Sintering Process

838485868788899091

Normal Sintering HIP Sintering

Sintering Process

Hard

ness

(HR1

5N)

10% Zr20% Zr

55

5

4.3 Density

In general density increases with higher content of zirconia for both

sintering methods. Density increase about 3.5% for Normal sintering and 5.4% for

HIP with incresing zirconia content from 10% to 20%. Effect of sintering method

was not significant for 20% zirconia content as compared to 10% of zirconia

content.

However density decreased about 2% for 10% zirconia sample when

sintered with different sintering process, from normal to HIP.

Result in Figure 4.3 indicate that the density was not in line with the

theoretical values. Theoretically HIP is expected to produce a higher density as

compared to normal sintering, deu to the pressure that applied together with

temperature. This will help to remove all the air bubbles in the green body,

however the result showed that the density for 10% zirconia was better with normal

sintering.

This maybe due to the experiments error and probably due to the equipment

that was used in the process. However the overall resultt for the density can be

accepted because of the small percentage of differentiation between the two

sintering methods.

Figure 4.3 : Density with different zirconia composition

Density With Different Zirconia Composition

3.93.95

44.054.1

4.154.2

4.254.3

10% Zr 20% Zr


Den

sity

(g/c

m3)


56

5

Figure 4.4 : Density with different sintering process

4.4 Shrinkage

In general, lower shrinkage value was recorded with higher content of

Zirconia regardless of the sintering processes, except for the thickness shrinkage in

the normal sintering.

Diameter and thickness shrinkage were found to decrease around 3.7% -

0.2% for normal sintering process for 10% to 20% of zirconia. Higher shrinkage

value was found for samples produce by HIP sintering process with recorded value

of 4.5% - 7.5%.

The diameter shrinkage and thickness shrinkage of the various samples are

shown in Figure 4.5 and 4.6 respectively.

Density After Different Sintering Process

3.93.95

44.054.1

4.154.2

4.254.3

Normal Sintering HIP Sintering

Sintering Process

Dens

ity (g

/cm

3)

10% Zr20% Zr

57

5

Figure 4.5 : Diameter shrinkage

Figure 4.6: Thickness shrinkage

4.5 Surface Roughness

In general surface roughness (Ra) value increases with increase in zirconia

content, and normal sintering process produce a lower roughness value as to HIP.

As shown in Figure 4.7.

DIAMETER SHRINGKAGE

15

15.2

15.4

15.6

15.8

16

16.2

16.4

10% Zr 20% Zr


Shr

ingk

age

Per

cent

age

(%)


THICKNESS SHRINGKAGE

15

15.5

16

16.5

17

10% Zr 20% Zr

Zirconia Composisition

Shrin

gkag

e Pe

rcen

tage

(%)


58

5

Graphical result showed that the surface roughness value for 20% zirconia

samples had a higher roughness values as compared to 10% zirconia sample.

Similar result were observe for both sintering method. Overall the surface

roughness of samples produce from normal sintering were slightly lower than HIP

sintering, however the different was marginal.

.

Figure 4.7 : Surface roughness with different zirconia composition.

4.6 Machinability

Result shows that for normal sintering process, the samples with 10%

zirconia content have a lower tool wear as compared to the samples with 20%

zirconia content.

The 20% zirconia content samples failed at 0.71 minutes while 10% zirconia

content samples failed at 2.14 minutes. This was probably due to the fracture

toughness of the 10% samples was higher than 20% samples, however the fracture

toughness cannot be measure because of unavailability of the equipment.

Surface Roughness With Different Zirconia Composition

0

0.2

0.4

0.6

0.8

1

1.2

1.4

10% Zr 20% Zr


Surf

ace

Roug

hnes

s (R

a)


59

6

In average, the 20% Zirconia sample failed at 0.71 min cutting time (VB >

0.5mm ), while 10% Zirconia sample failed at 2.14 min cutting time (VB >

0.5mm).

This is maybe because of the fracture toughness of the 10% sample is higher

than 20% sample, in this experiment fracture toughness cannot be measure because

lack of equipment.

In general when hardness is higher, the brittleness of the samples increases

which resulted in decrease of fracture toughness

For normal sintering (Figure 4.8), the tool life of the sample with 10%

zirconia content was better than the 20% zirconia samples. Thus indicates that the

former samples failed prematurely due to lack of fracture toughness.

Figure 4.8 : Tool wear with normal sintering process sample.

Normal Sintering

0.000.100.200.300.400.500.600.700.800.90

0.00 0.71 1.43 2.14

Cutting Time (min)

Flan

k W

ear V

B (m

m)

10% Zirconia20% Zirconia

60

6

As for the HIP sintering process, result shows that sample with 10% and

20% zirconia content resulted a similar tool wear. In average, both sample failed at

1.43 minutes. It maybe suggested that the sintering method have no significant

effect on the tool life performance of all samples due to the marginal different in

tool life accept for sample with 10% zirconia using normal sintering process.

The lower tool life recorded on all samples was probably due to the high

cutting condition selected.

Figure 4.9 : Tool wear with HIP sintering process sample.

HIP Sintering

0.000.100.200.300.400.500.600.700.80

0.00 0.71 1.43 2.14

Cutting Time, T (min)

Flan

k W

ear,

VB (m

m)

10% Zirconia20% Zirconia

61

6

Chapter 5

CONCLUSION

5.1 Conclusion

From all the testing and measuring that has been done in this study, the

following conclusion are drawn , Sample with 10% zirconia content have better

physical which include density, shrinkage, hardness and surface roughness

properties as compared to 20% zirconia content, with exception on the density. In

general normal sintering process produce samples with slightly better properties as

compared to HIP sintering.

The fabricated inserts have machining potential with further improvement

on the insert configuration, cutting parameters and tool holder. The effect of

sintering process on tool life were not significant except for sample with 10%

zirconia.

62

6

References

1. Physical behaviour of powder ceramic part using Cold Isostatic

Pressing (CIP) process, by Sarizal Md Ani, Mechanical

Engineering Faculty, UTM, Malaysia. (2006)

2. Alumina-Reinforced Zirconia Composites by Sung R. Choi,

Ohio Aerospace Institute, Ohio Narottam P. Bansal Glenn

Research Center, Cleveland, Ohio (2003)

3. Alumina ceramics with partially stabilized zirconia for cutting

tools by B. Smuk, M. Szutkowska, J. Walter Materials

Engineering Department, The Institute of Metal Cutting, ul.

Wrocławska 37a, 30-011 Krakow, Poland. (2003)

4. Machinability of hardened steel using alumina based ceramic

cutting tools by A. Senthil Kumar Department of Mechanical

Engineering, Anna University, Chennai, India (2003)

5. Preparation and characterization of an Al2O3–ZrO2

nanocomposite, by D. Sarkar, S. Adak , N.K. Mitra, Department

of Ceramic Engineering, National Institute of Technology, India

(2006).

6. The effect of tool wear on tool life of alumina-based ceramic

cutting tools while machining hardened martensitic stainless

steel, A. Senthil Kumara, A. Raja Durai, T. Sornakumar, Sethu

Institute of Technology, Madurai 626106, India (2006).

63

6

7. Manufacturing Engineering and Technology, Fourth Edition,

Serope Kalpakjian, Steven R Schmid, Prentice Hall International

2001.

8. Perspectives on the Development of Ceramic Composites or

Cutting Tool Applications by O. Van der Biest and J. Vleugels

Katholieke Universiteit Leuven, Kasteelpark Arenberg, Belgium

(2002).

9. Effect of the composition and sintering process on mechanical

properties and residual stresses in zirconia–alumina composites

by Giuseppe Magnania,, Aldo Brillanteb, ENEA, Bologna

Research Center, Italy, (2005).

10. Cutting Performance of High Purity Alumina Ceramic Tools

formed by a High-speed Centrifugal Compaction Process

Shunzo Tashima, Yasuo Yamane, Hidenori Kuroki and Norihiko

Narutaki Cluster & Fat. Eng. Hiroshima University, 1-4-l

figamiyama, Higashi-hiroshima 739 Japan (1996).

11. ZrO2–Al2O3 composites with tailored toughness by Bikramjit

Basu, Jozef Vleugels, Omer Van Der Biest, Ceramics

Laboratory, Department of Materials and Metallurgical

Engineering, Indian Institute of Technology, Kanpur, India,

Department of Metallurgy and Materials Engineering,

Katholieke Universiteit Leuven, Kasteelpark Arenberg 44, B-

3001 Leuven, Belgium (2004).

12. Study on the turning characteristics of alumina-based ceramics,

B.H. Yan , F.Y. Huang a, H.M. Chow, Department of

Mechanical Engineerin9, National Central University, Chuno-Li,

Taiwan, ROC Department of Mechanical Engineering, Nan Kai

Institute, Nan-Tou, Taiwan, ROC (1995).

64

APPENDIX 1 Picture of samples

APPENDIX 2 Machining sample 1

Figure 1 : After first cut.

Figure 2 : After 2nd cut.

Appendix 3 Machining sample 2



Appendix 1

2.8.1 Morgan Advance Ceramic USA

ZTA (Zirconia Toughened Alumina) is used in mechanical applications. It

is considerably higher in strength and toughness than Alumina. This is as a result

of the stress-induced transformation toughening achieved by incorporating fine

Zirconia particles uniformly throughout the Alumina. Typical Zirconia content is

between 10% and 20%. As a result, ZTA is more expensive than Alumina but

offers increased component life andperformance.

Typical characteristics include:

Excellent strength

Excellent toughness

Excellent wear resistance

High temperature stability

Corrosion resistance

Typical applications include:

Pump components

Bearings

Bushings

Cutting tool inserts

Valve seats

Wear components

2.10.2 Dynamic Ceramic England

Components manufactured from Zirconia Toughened Alumina (ZTA)

show considerable improvement in strength and toughness over alumina

engineering ceramics.

The increase in strength and toughness in ZTA is attributable to the stress

induced transformation toughening mechanism which is introduced with the

addition of optimized amounts of fine zirconia particles dispersed thoughout the

alumina body.

Typical zirconia content is between 10% and 20%. As a crack grows

through the ceramic, the crystal structure of the zirconia particles in the region of

the crack changes from the metastable tetragonal phase to the stable monoclinic

phase.

The change increases the volume of the particles by about 3-4% and

produces compressive stresses in the alumina matrix. These stresses in turn close

the crack and act as an energy barrier to further crack growth. The addition of

zirconia to the alumina matrix increases fracture toughness by two times and can

be improved by as high as four times, while strength is more than doubled.

Key Properties

• Excellent mechanical properties

• Wear resistance

• High temperature stability

• Corrosion resistance

Applications

ZTA components are more expensive than those in alpha alumina.

However, increased component life and performance result in cost effective

solutions for demanding environments.

Applications include:

• Bearing components (balls, rollers and raceways)

• Bushings

• Die and cutting tool inserts (replacing carbide and metal tool inserts)

• Valve seats

• Pump components

2.10.3 AZOM.com, A to Z material

Zirconia Toughened Alumina (ZTA) shows considerable improvement in

strength and toughness over standard alpha alumina. This is brought about

through the stress induced transformation toughening mechanism.

Stress Induced Transformation Toughening

ZTA is strengthened by fine zirconia particles uniformly dispersed

throughout the alumina body. Typical zirconia content is between 10% and 20%.

The properties are improved by a mechanism known as stress induced

transformation toughening. As a crack grows through the ceramic, the crystal

structure of the zirconia particles in the region of the crack changes from the

metastable tetragonal phase to the stable monoclinic phase. The change increases

the volume of the particles by about 3% and produces compressive stresses in the

alumina matrix. These stresses in turn close the crack and act as an energy barrier

to further crack growth. The addition of zirconia to the alumina matrix increases

fracture toughness easily by two times and can be improved by as high as four

times, while strength is more than doubled.

ZTA components are more expensive than those in alpha alumina.

However, increased component life and performance result in cost effective

solutions for demanding environments.

Applications include:

- Bearing components (balls, rollers and raceways)

- Bushings

- Die and cutting tool inserts (replacing carbide and metal tool inserts)

- Valve seats

- Pump components

2.10.4 Cetek Technologies, Inc.

Zirconia Toughened Alumina is produced by a carefully controlled

process to yield transformation toughened ZTA material. They use very pure

yttria partially-stabilized zirconia raw materials to produce a monoclinic to

tetragonal phase ZTA ceramic. Typical zirconia content is between 10% and 20%.

ZTA offers increased component life and performance compared to alumina.

They have the ability to engineer the properties of the ZTA to improve its

thermal conductivity and thermal shock characteristics. Excellent Strength,

Industrial Toughness, Ideal Wear Resistance, High Temperature Stability and

Corrosion Resistance are some of our ZTA's typical characteristics.

development of ceramic cutting tool insert of

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