DEVELOPMENT OF CERAMIC CUTTING TOOL INSERT OF
ALUMINA (Al2O3) AND ZIRCONIA (ZrO2) FOR TURNING
HARDENED TOOL STEEL
ZURAIDY BIN SHAMSUDIN
UNIVERSITI TEKNOLOGI MALAYSIA
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
iii
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.
iv
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.
v
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.
vi
CONTENTS
CHAPTER
1
2
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
INTRODUCTION
1.1
General Background
1.2
Problem Statement
1.3
Objective
1.4
Scope of the Project
1.5
Expected Results
LITERATURE REVIEW
2.1
Introduction
2.2
Ball milling
vii
2.3
Hot Isostatic Press
2.4
Ceramic material
2.4.1
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
2.9
3
Properties of ceramic
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
Previous research related to current study
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
viii
4
5
RESULTS AND DISCUSSION
4.1
Introduction
4.2
Hardness
4.3
Density
4.4
Shrinkage
4.5
Surface roughness
4.6
Machinability
CONCLUSION
REFERENCES
APPENDICES 1 - 22
ix
LIST OF TABLES
TABLE NO.
TITLE
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
PAGE
LIST OF FIGURES
FIGURE NO.
TITLE
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
PAGE
x
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
xi
LIST OF APPENDICES
APPENDIX NO.
TITLE
1
Pictures of samples
2
Machining sample 1
3
Machining sample 2
4
Machining sample 3
5
Machining sample 4
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
xii
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
11
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.
22
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 aluminazirconia composite powder will be established.
3
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.
4
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
5
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].
6
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
7
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].
8
Figure2.3 : Hot Isostatic Press machine
Figure 2.4: Example of Hot Isostatic Press process – diffusion bonding
99
Figure 2.5 : Isostatic vs Uniaxial
Figure 2.6: Isostatic shape change
10
1
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]:
111
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.
1
12
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.
1
13
Figure 2.7 show the various properties of ceramic materials [10].
Table 2.1: Properties of various ceramics at room temperature
Material
Symbol
Compressive
Elastic
Strength
Modulus
Hardness
Density
(Mpa)
(GPa)
(HK)
(kg/m3)
Alumina
Oxide
Al2O3
1000-2900
310-410
20003000
40004500
Cubic boron
nitride
CBN
7000
850
40005000
3480
Silicon
nitride
Si3N4
No data
300-310
20002500
3300
Silicon
carbide
SiC
700-3500
240-480
21003000
3100
Titanium
carbide
TiC
3100-3850
310-410
18003200
55005800
Tungsten
carbide
WC
4100-5900
520-700
18002400
1000015000
1
14
Figure 2.7 : Material comparison chart from Kyocera [10].
1
15
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
1
16
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].
1
17
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
1
18
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
119
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.
2
20
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
2.7
Hexagonal
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 :
2
21
2.8
-
Wear resistance
-
High temperature stability
-
Corrosion resistance
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
1.
Sarizal
Topic
Md
Finding
Ani, Physical behaviour Produce alumina samples
Mechanical Engineering of powder ceramic
with
CIP
process
Faculty, UTM, Malaysia. part
(2006)
using
Isostatic
Cold
compaction
and
normal
sintering process.
Pressing He found that the hardness
(CIP) process
increase was very small
amount
within
1.0%
to
1.5% for each different
pressurization and timing.
Average hardness value at
sintering
0
1300 C,
0
1700 C
temperature
15000C
and
were
68.3
222
(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
Aerospace
Brook
Narottam
Park,
P.
Ohio Alumina-
Alumina-reinforced zirconia
Institute, Reinforced
composites was fabricated
Ohio Zirconia
by hot pressing 10 mol%
Bansal Composites
yttria-stabilized
zirconia
Glenn Research Center,
(10-YSZ) reinforced with
Cleveland, Ohio (2003).
two
different
forms
alumina—particulates
of
and
platelets—each containing 0
to 30 mol% alumina.
At
ambient
temperature,
both flexure strength and
fracture toughness increased
with
increasing
content,
alumina
reaching
a
maximum at 30 mol%.
Vickers microhardness of
the particulate composites
increased with increasing
2
23
alumina
content;
while
Vickers microhardness of
the
platelet
composites
followed an opposite trend,
in
which
decrease
a
significant
in
hardness
resulted in higher alumina
contents
3
B.
Smuk,
M. Alumina ceramics A series of ceramic tool
Szutkowska, J. Walter with
partially
materials based on Al2O3
with ZrO2.
Materials
Engineering stabilized zirconia
Department, The Institute for cutting tools
of Metal Cutting, ul.
The
alumina
ceramics
obtained with the addition
of 20 mass% of the zirconia
stabilized
(ZY5)
and
Wrocławska 37a, 30-011
sintered at 1615 oC for 60
Krakow, Poland. (2003).
min are characterized by the
best mechanical properties
from
among
the
tested
compound
compositions.
This
of
type
alumina
ceramics gives greater wear
resistance, TRS (even about
80%), tool life of the cutting
edge and better toughness at
the
same
comparison
Al2O3
hardness,
with
in
pure
ceramics.
Preliminary industrial tests
confirm the high cutting
2
24
performance
ceramic
of
alumina
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. Perspectives on the In
Vleugels Department of
Development
of
Metallurgy and Materials
Engineering, Katholieke
Universiteit
Arenberg,
44,
Heverlee,
B-3001
Ceramic
the
requirements for ceramic
for machining iron based
Cutting
or alloys are reviewed, taking
Tool
into account the trends in
the industry towards dry
Applications
Belgium (2002).
paper
composites as cutting tools
Leuven, Composites
Kasteelpark
this
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,, Effect
of
Aldo Brillanteb, ENEA, composition
the Zirconia-toughened alumina
and
(ZTA) with small amounts
of
Bologna
Research sintering process on
Center, Via dei Colli, mechanical
40136
Bologna,
Italy, properties
chromia
magnetoplumbite-type
crystalline
and
phase
(CeMgAl11O19) have been
prepared
University of Bologna, residual stresses in
and
and
processed
under different conditions.
2
25
Department of Physical zirconia–alumina
Main results are:
The
and Inorganic Chemistry, composites
highest
fracture
40136
Bologna,
Italy
value
toughness
of
was
achieved with pressureless
(2005).
sintering of the composite
containing
chromia
0.5
wt.% and yttria 2 mol%.
Post-hot isostatic pressing
treatment
formation
quantity
caused
of
of
a
the
small
monoclinic
phase that reduced fracture
toughness.
Transformability
strongly
was
affected
by
stabilizer content.
Chromia addition led to an
enhancement of the fracture
toughness.
Stress-induced
transformation
toughening
is
mechanism
the
responsible for the fracture
toughness improvement.
6
In this study by using a
Shunzo Tashima, Yasuo Cutting
Hidenori Performance
Yamane,
of
high-speed
centrifugal
compaction process, a slip
Kuroki
and
Norihiko High
Narutaki Cluster & Fat. Alumina
Eng.
Purity
prepared
from
alumina
Ceramic powder with a purity of
Hiroshima Tools formed by a
99.99 % and an average
particle size of 0.22 D m
University,
1-4-l High-speed
2
26
figamiyama,
hiroshima
Higashi- Centrifugal
739
was
compacted,
and
sintered at 1230 “C for 1.5
Japan Compaction
hours in the atmosphere.
(1996)
Process
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
subject
using
high
centrifugal
-
the
speed
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. Machinability
Raja
Durai
,
T. hardened
of In
steel
this
paper
the
machinability of hardened
steel using alumina based
Sornakumar
using
alumina
,Manufacturing
based
ceramic materials is analysed.
Engineering
Division, cutting tools
ceramic
cutting
tool
Abrasive wear is found to
be the predominant wear
Department
of
Mechanical Engineering,
Anna
University,
mechanism
in
alumina
based ceramic cutting tool
materials when machining
hardened steel.
Chennai 600025, Indiab
Zirconia toughened alumina
2
27
Department
of
ceramic tool is not affected
by diffusion wear. Surface
Mechanical Engineering,
finish
Thiagarajar College of
Engineering,
Madurai
both
N.K. Mitra, Department
Technology,
of
ceramic
and In this study the fine ZrO2
characterization of
of Ceramic Engineering,
Institute
types
cutting tool materials.
D. Sarkar, S. Adak , Preparation
National
with
increasing cutting speed for
625015, India (2003).
8
improves
of
homogeneously
an
Al2O3–ZrO2
Rourkela nanocomposite,
769008, Orissa, India,
Part
I:
dispersed
within the alumina matrix
with a maximum grain size
Powder
Department of Chemical
Technology, University
(100–300 nm) has been
of _0.8 lm, which will
increase the toughness of
synthesis
and
the alumina matrix.
of Calcutta, 92, A.P.C. transformation
Road, Kolkata 9, India
behavior
during
(2006)
fracture
9
Bikramjit
Basu,
Jozef ZrO2–Al2O3
Vleugels, Omer Van Der
Biest,
with
Ceramics
Laboratory, Department
of
composites
In this paper their found that
Materials
and
Metallurgical
Engineering,
the toughness of Y-TZP
based composites with 20
tailored toughness
wt.%
Al2O3
increased
by
be
careful
engineering of the ZrO2
Indian
matrix by means of the
Institute of Technology,
“mixing route”.
Kanpur,
The
Department
can
India,
optimum toughness,
of
pursued in this route, is
Metallurgy and Materials
much higher than that of the
Engineering, Katholieke
commercial co-precipitated
Universiteit
powder
Leuven,
based
ceramics,
2
28
Kasteelpark
44,
Arenberg
B-3001
sintered under the same
Leuven,
experimental
Belgium (2004)
The
conditions.
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, Study
on
the It is found that PCD tool is
superior to the other tools,
H.M. Chow, Department turning
whilst the carbide tool and
Mechanical characteristics
of
National alumina-based
Engineerin9,
University, ceramics
Central
of
the
ceramic
tool
are
unsuitable for machining
ceramics materials. It is
found that, despite their
Chuno-Li, Taiwan, ROC
Department
of
Mechanical Engineering,
brittle nature, cutting finesintered ceramics with a
PCD tool at the optimum
cutting conditions of cutting
Nan Kai Institute, NanTou,
(1995).
Taiwan,
ROC
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
2
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. The effect of tool Zirconia toughened alumina
Raja
Durai,
T. wear on tool life of
ceramic
cutting
tool
is
affected by the flank wear at
Sornakumar, Department alumina-based
of
Engineering,
Production ceramic
lower
speed
but
it
is
cutting affected by notch wear at
Sethu tools
while
higher speed.
Machining tests have been
Institute of Technology, machining
carried out in a precision
Madurai 626106, India hardened
lathe, using these alumina(2006).
martensitic
based ceramic cutting tools
stainless steel
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
3
30
using tool room microscope
and micro stylus attached
dial gauge.
313
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)
2
o
HIP sintering (1700 C +200Mpa)
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 .
333
Table 3.2 : Experiment planning
Code
Zirconia Content
Sintering Process
Sample 1
Z-10-N1
10%
Normal
Sample 2
Z-10-N2
10%
Normal
Sample 3
Z-10-N3
10%
Normal
Sample 4
Z-10-H1
10%
HIP
Sample 5
Z-10-H2
10%
HIP
Sample 6
Z-10-H3
10%
HIP
Sample 7
Z-20-N1
20%
Normal
Sample 8
Z-20-N2
20%
Normal
Sample 9
Z-20-N3
20%
Normal
Sample 10
Z-20-H1
20%
HIP
Sample 11
Z-20-H2
20%
HIP
Sample 12
Z-20-H3
20%
HIP
Machining Parameters
Cutting Speed : V = 150
Feed Rate : 0.12mm/rev
Depth of Cut : 0.5mm
Condition : Dry Cutting
334
3.4
Experimental Flow Chart
ALUMINA + ZIRCONIA
10%
ZIRCONIA
6 samples
20%
ZIRCONIA
6 samples
BALL MILL PROCESS
MANUAL PELLET PRESS WITH INSERT MOLD
200 Mpa - 30 sec
2 compositions x 6 samples = 12 samples
NORMAL SINTERING
1700oC
-
Hardness
Density
Surface Roughness
Shrinkage
Machinability
HOT ISOSTATIC PRESS
1700oC + 200Mpa
-
Hardness
Density
Surface Roughness
Shrinkage
Machinability
Figure 3.1 : Process Flow Chart
3
35
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.
3
36
Figure 3.2 : Powder preparation process
Figure 3.3 : Manual pallet press process
3
37
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
3
38
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.
3
39
Figure 3.6 : HIP furnace
Figure 3.7 : Samples inside HIP furnace chamber
440
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
vsample = vcell −
vexp
p1g
−1
p2 g
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
441
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
442
Figure 3.9:
3.6
Carver Pallet Dies with 13mm diameter.
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.
4
43
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
1700OC under vacuum
temperature
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
8.50 KW @ 1800OC and 30000 PSI
consumtion
Furnace weight
20 pounds ( 454 g )
Maximum workload
20 pounds ( 454 g )
weight
Maximum air exposure
200oC
temperature
4
44
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
445
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
4
46
Figure 3.13 : Automatic tool change at the SL20
Figure 3.14: Tool holder for the experiment.
447
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.
4
49
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.
515
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.
5
52
Figure 3.20 : Tool maker microscope Mitutoyo to measure the tool wear
553
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.
5
54
This maybe deu to the purity of ceramic powder, temperature error, etc,
however the different was marginal as shown in Figure 4.2.
Hardness With Different Zirconia Composition
Hardness (HR15N)
91
90
89
88
Normal Sintering
87
HIP Sintering
86
85
84
83
10% Zr
20% Zr
Zirconia Composition
Figure 4.1 : Hardness with different zirconia composition
Hardness With Different Sintering Process
H a rd n e s s (H R 1 5 N )
91
90
89
88
10% Zr
87
20% Zr
86
85
84
83
Normal Sintering
HIP Sintering
Sintering Process
Figure 4.2 : Hardness with different sintering process
5
55
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.
Density With Different Zirconia Composition
4.3
Density (g/cm 3)
4.25
4.2
4.15
Normal Sintering
4.1
HIP Sintering
4.05
4
3.95
3.9
10% Zr
20% Zr
Zirconia Composition
Figure 4.3 : Density with different zirconia composition
556
Density After Different Sintering Process
4.3
Density (g/cm 3)
4.25
4.2
4.15
10% Zr
4.1
20% Zr
4.05
4
3.95
3.9
Normal Sintering
HIP Sintering
Sintering Process
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.
5
57
Shringkage Percentage (% )
DIAMETER SHRINGKAGE
16.4
16.2
16
15.8
Normal Sintering
15.6
HIP Sintering
15.4
15.2
15
10% Zr
20% Zr
Zirconia Composition
Figure 4.5 : Diameter shrinkage
Shringkage Percentage (%)
THICKNESS SHRINGKAGE
17
16.5
Normal Sintering
16
HIP Sintering
15.5
15
10% Zr
20% Zr
Zirconia Composisition
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.
558
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.
.
Surface Roughness With Different Zirconia Composition
Surface Roughness (Ra)
1.4
1.2
1
0.8
Normal Sintering
0.6
HIP Sintering
0.4
0.2
0
10% Zr
20% Zr
Zirconia Composition
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.
5
59
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.
Flank Wear VB (mm)
Normal Sintering
0.90
0.80
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0.00
10% Zirconia
20% Zirconia
0.00
0.71
1.43
2.14
Cutting Time (min)
Figure 4.8 : Tool wear with normal sintering process sample.
606
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.
HIP Sintering
Flank Wear, VB (mm)
0.80
0.70
0.60
0.50
10% Zirconia
0.40
20% Zirconia
0.30
0.20
0.10
0.00
0.00
0.71
1.43
2.14
Cutting Time, T (min)
Figure 4.9 : Tool wear with HIP sintering process sample.
6
61
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.
662
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).
663
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, B3001 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).
6
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
Figure 1 : After first cut.
Figure 2 : After 2nd cut.
Appendix 4
Machining sample 3
Figure 1 : After first cut.
Figure 2 : After 2nd cut.
Appendix 5
Machining sample 4
Figure 1 : After first cut.
Figure 2 : After 2nd cut.
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.