Effect Of Yeast Content As Foaming Agent On The Mechanical Properties Of Titanium Foam.
SUPERVISOR DECLARATION
“I hereby declare that I have read this thesis and in my opinion this thesis is
sufficient in terms of scope and quality for the award of the degree of Bachelor of
Mechanical Engineering (Structure and Materials)”
Signature
:
Supervisor
: DR. MOHD ZULKEFLI BIN SELAMAT
Date
:
EFFECT OF YEAST CONTENT AS FOAMING AGENT ON THE
MECHANICAL PROPERTIES OF TITANIUM FOAM
NURUL FARHANA IZZATI BINTI MOHAMAD NAZRI
This thesis is submitted in partial fulfillment of the requirement for the award
of Bachelor of Mechanical Engineering (Structure and Materials) (HONS.)
Faculty of Mechanical Engineering
Universiti Teknikal Malaysia Melaka
JUNE 2015
iii
DECLARATION
“I hereby declare that the work in this thesis is my own except for summaries and
quotations which have been duly acknowledged.”
Signature
:
Author
: NURUL FARHANA IZZATI BINTI MOHAMAD NAZRI
Date
:
iv
Dedicated to my family
especially for my mother and father
v
ACKNOWLEDGEMENT
I would like to take this opportunity to express my greatest gratitude to the
people who have been instrumental in the successful completion of this Final Year
Project. This project would not been possible without the support of them.
I wish my deepest thanks and appreciate to my final year project supervisor,
Dr Mohd Zulkefli bin Selamat, who was abundantly helpful and offered invaluable
assistance, support and guidance. Without his encouragement and guidance, this
project would not have materialized. Thanks also to the lecturers and lab assistants
who had guide me to complete this project. I warmly thank to my friends for their
valuable advice and friendly help. Last but not least, I wish to express my love and
gratitude to my beloved families for their understanding and endless love through the
duration of my studies.
Without helps of the particular that mentioned above, I would face many
difficulties in completing this project.
vi
ABSTRACT
Nowadays, metal foam has gained interest in industry and became so popular. Its
physical and mechanical properties are believed to give various benefits to various
industries such as automotive, aerospace and biomedical application. Mechanical
properties of metal foam such as light-weight structure, energy absorption, high
stiffness and low Young’s modulus has entrusted the researchers to study the nature
of the metal foam deeper for future benefits. This research succeed to achieve the
research objectives which is to determine the effect of yeast content on the
mechanical properties of titanium foam and study the effect of yeast content on the
size of micro pores. Yeast as new organic foaming agent is proved as a replacement
for existing foaming agent. Yeast weight percentage that have been used are 15, 25
and 30 wt. %. Titanium foam was made up with slurry technique with yeast as
foaming agent and ethylene glycol as binder. The yeast decomposed during the
sintering process and thus, it is environmental friendly. Different ratio of titanium
powder to yeast was used to obtain the best result of titanium foam. The
microstructure of the titanium foam was analysed using inverter microscope and
image analyser was used to obtain the details of microstructure of titanium foam
result. The pore size of titanium foam obtained was in range of 395.63 to 546.78 µm
while the strut size obtained was in the range of 223.13 to 300 µm. The porosities of
titanium foam lead to 60.5 until 75.5%. Furthermore, mechanical testing such as
compression test was carried out. From the compression stress held, Young’s
Modulus can be known. Compression stress of 2.41 to 4.56MPa and Young’s
Modulus of 0.218 to 0.267GPa were obtained. All the results obtained fulfil the
requirements of human cancellous bone.
vii
ABSTRAK
Pada masa kini, logam berbusa telah mendapat tarikan daripada industri dan menjadi
begitu popular. Sifat-sifat fizikal dan mekanikal yang dipercayai memberi pelbagai
manfaat untuk pelbagai industri seperti aplikasi pada automotif, aeroangkasa dan
bioperubatan. Sifat mekanikal logam berbusa seperti struktur ringan, penyerapan
tenaga, kekakuan tinggi dan modulus Young yang rendah telah memberi
kepercayaan pada para penyelidik untuk mengkaji sifat logam berbusa dengan lebih
mendalam untuk faedah masa depan. Kajian ini berjaya mencapai objektif kajian
iaitu untuk menentukan kesan kandungan yis pada sifat-sifat mekanikal titanium
berbusa dan mengkaji kesan kandungan yis kepada saiz liang mikro. Yis sebagai ejen
berbuih organik baru terbukti boleh digunakan untuk menggantikan ejen berbuih
sedia ada dan peratusan berat yis telah digunakan adalah 15, 25 dan 30%. Busa
titanium dibuat dengan teknik buburan dengan yis sebagai ejen berbuih dan etilena
glikol sebagai pengikat. Yis mengurai semasa proses pensinteran dan dengan itu, ia
adalah mesra alam sekitar. Nisbah serbuk titanium kepada yis yang berbeza akan
digunakan untuk mendapatkan hasil titanium berbusa yang terbaik. Mikrostruktur
titanium berbusa telah dianalisis dengan menggunakan inverter mikroskop dan
penganalisis imej telah digunakan untuk mendapatkan butir-butir mikrostruktur hasil
titanium berbusa. Saiz liang busa titanium diperolehi ialah dalam julat 395.63-546.78
µm manakala saiz tupang yang diperolehi adalah dalam julat 223.13-300 µm.
Keporosan busa titanium yang diperolehi adalah antara 60.5 sehingga 75.5%.
Tambahan pula, ujian mekanikal seperti kekuatan mampatan telah dijalankan.
Daripada ujian tekanan mampatan yang dijalankan, Modulus Young dapat diketahui.
Tekanan mampatan bernilai 2.41 hingga 4.56MPa dan Modulus Young bernilai
0.218 hingga 0.267GPa telah diperolehi. Semua keputusan penyelidikan yang
diperolehi memenuhi keperluan tulang cancellous manusia.
viii
TABLE OF CONTENT
CHAPTER
TITLE
PAGES
SUPERVISOR DECLARATION
i
STUDENT DECLARATION
iii
DEDICATION
iv
ACKNOWLEDGMENT
v
ABSTRACT
vi
ABSTRAK
vii
TABLE OF CONTENT
viii
LIST OF TABLES
xi
LIST OF FIGURES
xii
LIST OF SYMBOLS
xv
LIST OF APPENDDICES
xvi
ix
CHAPTER 1 INTRODUCTION
1
1.0
Introduction
1
1.1
Project Objectives
3
1.2
Problem Statement
3
1.3
Project Scope
4
CHAPTER 2 LITERATURE REVIEW
5
2.0
Introduction
5
2.1
Biomedical Application of Metal Foam
6
2.1.1
Mechanical Properties of Cancellous Bone
7
2.1.2
Porosity in Bone Implant
9
2.2
2.3
2.4
2.5
2.6
Material Selection
12
2.2.1
Properties of Titanium
13
2.2.2
Mechanism of Yeast
14
Metal Foams from Metal Powder
15
2.3.1
Sintering of Metal Powders and Fibres
15
2.3.2
Sintering of Hollow Spheres
16
2.3.3
Gas Entrapment
17
2.3.4
Foaming of Slurries
18
2.3.5
The Addition of Space-holding Fillers
18
2.3.6
Extrusion of Metal Mixtures
19
Mechanical Testing of Titanium Foam
20
2.4.1
Compression Test
20
2.4.2
Hardness Test
21
Characterisation of Pore
22
2.5.1
Pore Microstructure
22
2.5.2
Density
23
Research Focus
23
x
CHAPTER 3 METHODOLOGY
24
3.0
Introduction
24
3.1
Fabrication Process
24
3.2
Raw Material
26
3.3
Development of Porous Titanium Specimen
by Sintering Process
29
3.4
Mechanical Testing
31
3.5
Characterisation of Titanium Foam Microstructure
32
CHAPTER 4 RESULTS AND ANALYSIS
34
4.1
Introduction
34
4.2
Microstructure Analysis of Titanium Foam
34
4.2.1
Result
35
Porosity and Density
37
4.3.1
37
4.3
4.4
Result
Compression Test and Young’s Modulus
39
4.4.1
39
Result
CHAPTER 5 DISCUSSION
41
5.1
Microstructure of Titanium Foam
41
5.2
Porosity and Density
42
5.3
Compression Strength and Young’s Modulus
43
5.4
Comparison between Cancellous Bone and Titanium
Foam
45
CHAPTER 6 CONCLUSION
46
6.1
Conclusion
46
6.2
Recommendations
47
REFERENCES
48
APPENDIX
52
xi
LIST OF TABLES
NO
TITLE
2.1
The mechanical properties of cancellous bone
2.2
The mechanical properties of metals used in orthopaedic
PAGES
9
application
14
3.1
Properties of titanium powder
26
3.2
Properties of yeast
27
3.3
Composition of titanium powder and yeast
27
3.4
Titanium foam ready to be put in the furnace
29
4.1
Average pore size and strut size of titanium foam
35
4.2
Microstructure of titanium foam
36
4.3
Average density and porosity of titanium foam
37
4.4
Average compressive stress and Young’s Modulus of titanium
foam
5.1
39
The comparison between present research, human cancellous bone
and fabricated titanium foam from other research
45
xii
LIST OF FIGURES
NO
TITLE
2.1
Cancellous bone and cortical bone
2.2
The vertebra and the end of femur are filled with a
PAGES
7
spongy structure called cancellous bone
8
2.3
X-ray femur which shows cortical bone and cancellous bone
8
2.4
X-ray of: (1A) Normal healthy hip, (1B) Total hip replacement
10
2.5
Bone ingrowth into the pores ensure stable fixation
10
2.6
Figure 2.6 (a) Normal stresses flow in human body weight,
(b) Stress shielding occurs at the implant area
11
2.7
Styrofoam coating process for making hollow sphere structures
16
2.8
Gas Entrapment technique
17
2.9
Schematic illustration of the production of the titanium foams
18
2.10
The schematic process of space-holder technique
19
2.11
Process for making cellular metals with oriented porosity
from metal powders
20
xiii
2.12
Stress-strain graph of an orthopaedic titanium alloy tested
in tension
21
3.1
Flow chart of slurry technique in the research
25
3.2
Titanium powder (Ti6 – Al4– V)
26
3.3
Yeast
27
3.4
PVC pipe mould
28
3.5
Titanium slurry in the mould at room temperature
28
3.6
Vacuum furnace
30
3.7
Sintering cycle for the preparation of the titanium foam
30
3.8
Compression testing on titanium foam sample
31
3.9
Universal Testing Machine Instron 5585
31
3.10
Grinding and Polishing Machine
32
3.11
Samples in mounting cup
32
3.12
Inverter Microscope
33
3.13
Electronic densimeter
33
4.1
Pore morphology of fabricated titanium foam at 85% titanium
weight composition to 15% yeast weight composition.
4.2
Pore morphology of fabricated titanium foam at 75% titanium
weight composition to 25% yeast weight composition.
4.3
36
36
Pore morphology of fabricated titanium foam at 70% titanium
weight composition to 30% yeast weight composition.
36
4.4
Effect of Yeast Weight Composition to Density
38
4.5
Effect of Yeast Weight Composition to Porosity
38
xiv
4.6
Effect of Yeast Weight Composition to Compression stress
and Young’s Modulus
5.1
Effect of different yeast weight composition to pore size
and strut size
5.2
40
42
The effect of porosity to compressive stress and Young’s
Modulus of fabricated titanium foam
44
xv
LIST OF SYMBOLS
*
s
= density of foam
= density of solid material
= porosity
= volume of pore space
= total volume of sample
xvi
LIST OF APPENDICES
NO
TITLE
PAGES
1
Gantt Chart PSM I
53
2
Gantt Chart PSM II
54
3
The results of the pore size and strut size for titanium foam
4
The test results of density for titanium foam
56
5
Graph of compression test
57
55
CHAPTER 1
INTRODUCTION
1.0
BACKGROUND
Porous materials are easy to be found in the natural structure such as cork,
wood, bone and sponge. All of these natural structures have a great structural
strength yet lightweight. Therefore, man has applied this natural condition to the
man-made porous material from metal and ceramics. Those made have been widely
exploited because of the unique combination of physical and mechanical properties
offered by porous metals [1].
The characteristic of metallic foam is a combination of properties of metal
and foam. Metal foam is a gas bubble-filled substance made out of metal. It is a
structural material that contains a high volume of porosity within a metal and
typically very lightweight due to the low density [2]. Metal foam has been widely
used around the world involving aerospace, automotive, structural and biomedical.
Their applications are still promising and perspective even it had been introduced
over half of the centuries. It gives many beneficial in term of mechanical properties,
for
2
instance, high impact energy absorption, high stiffness, high strength to weight
ratios, high gas permeability, and high thermal conductivity [2].
The physics of metal foaming contains five stages which are making the
precursor, initial pore formation, pore inflation, foam degradation and solidification.
Mixture of metal powder and gas-releasing foaming agent is compacted to make the
precursor. While the precursor is on heating, gas evolves in the precursor and process
of pore formation begins to start. Pore formation is continually enlarged as the
foaming agent is decomposed. The ongoing gas supply from the decomposition of
foaming agent boosts the pore formation. Degradation begins while pores are being
inflated. Drainage occurs due to the downward flow of liquid through Plateau border
under gravity and bubbles coalesce as films become thin and unstable. The metal has
to be solidified quickly at the right time to prevent this unstable foam from collapse.
Deformation of films or crack may occur in the cell walls due to sudden
solidification [2].
The pore characteristics are divided into pore morphology, porosity and pore
size. Pore morphology is divided into open and closed pores. The difference between
both of it is in term of permeability where fluid can penetrate. Open pores are
penetrating pores while closed pores are non-penetrating. Open pores are very
important for separation-filtration while closed pores are beneficial for light-weight
materials and heat insulating materials [3].
The porosity means the fraction of pore volume to the total volume. Higher
porosity leads to lower Young Modulus. Thus, metal foam with smaller pores
generally has better elastic of modulus than metal foam with larger pores at an
equivalent porosity. Range of porosity will also influence thermal and electrical
conductivity, thermal shock resistance and gas permeability besides mechanical
properties [3].
3
1.1
PROJECT OBJECTIVES
The objectives of this research is to determine the effect of yeast content on
the mechanical properties of titanium foam and study the effect of yeast content on
the size of micro pores.
1.2
PROBLEM STATEMENT
Nowadays, use of titanium in biomedical application became so attractive and
popular due to its great corrosion resistance, biocompatibility and high strength to
weight ratio. However, elastic modulus of titanium, which is 110.3 GPa, is too high
compared to elastic modulus of human bone, which is in the ranges of 0.09–1.5 GPa
while for its compressive yield strength is 40–150 MPa [4]. This condition may lead
to stress shielding to the bone. Stress shielding is occurred due to the mismatch of
Young’s Modulus between the bone and metallic implants [5].
Hence, porous titanium is introduced to reduce the Young’s modulus and
thus, increased the productivity of titanium use in biomedical application. In this
research, a method of titanium foam preparation with yeast as foaming agent is
introduced and its mechanical properties in term of Young modulus and strength is
investigated; thus, study size of micro pores affected by yeast content. Heat causes
yeast to decompose and release gas, which then propels the foaming process. The
porous titanium had been fabricated using mixture of yeast and titanium powder by
controlling the ratio of yeast to titanium powder [6]. The mechanical properties and
pore structure of titanium foam obtained from this research could be mimicking to
those of the human bone.
4
1.3
PROJECT SCOPE
This research studied about the effect of yeast content as pore foaming agent
on the micro pores and mechanical properties of titanium foam as macro-porous
materials. In this research, the method used to prepare titanium foam is slurry
method. Titanium foam was being produced by preparing slurry of titanium powders
mixed with yeast as foaming agent. Preparation of slurry had started by mixing up of
yeast with titanium powder and ethylene glycol as binder. Certain amount of distilled
water was added to the mixture of titanium powder, yeast and binder for stir mixing.
Then, the slurry was mixed until the compounds were distributed evenly. After that,
the slurry was poured into the PVC mold and allowed it to dry under the room
temperature. The process was followed by sintering process with the temperature of
1250oC for 2 hours and with sintering rate of 5oC/min.
Different ratio of yeast to titanium powder was the processing parameter that
should be taken care during production of titanium foam to achieve these objectives.
This research investigated the suitability of production of titanium foam from the
mixture of titanium powder and yeast through slurry method. In determining the
mechanical properties, the compressive test had been carried out, the microstructures
of sintered porous materials were observed and the pores sizes were measured. The
mechanical properties and pore structure of titanium foam were investigated to
ensure it was closely resemble those of the human bone.
CHAPTER 2
LITERATURE REVIEW
2.0
INTRODUCTION
In 8 May 1943, Benjamin Sosnick is the person who had invented metal
foam. He had filed a patent entitled “Process for making Foam like Mass of Metal”.
He first melted a mix of 90 parts of aluminium, Al, to 10 parts of mercury, Hg, in a
closed chamber or under conditions to prevent the mercury vapour to escape. When
Hg in the mixture is stabilized, the pressure was released. This led to volatilizing of
Hg in the mass and thus, foam was formed [2, 7].
Nowadays, the application of metal foam becomes so popular and plays an
important role in industries due to its advantages. It is applied in a wide range of
sectors and industries which include transportation, defense, architecture, aviation,
marine, energy and process industries.
Metal foam is introduced to improve crash energy absorption at crash boxes
and bumper beams in the automotive industry. Besides, in Korea, some foam has
also been deployed in muffler system to reduce noise compared to regular muffler[8].
6
In aerospace, metal foam structural parts are being considered for turbine
component and as reinforcement for load bearing structures in satellites. Boeing also
had evaluated the use of large aluminium and titanium foam sandwich parts for tail
booms of helicopter [8]. The application of metal foams in railway is concerning
lightweight construction, energy absorption and damping insulation. In Japan, to
improve crash energy absorption, the trains has been fitted out with a 2.3 m3 block of
“Alporas” foam [9].
Moreover, open porosity metal foam also is applied as heat exchanger. Heat
can be removed from or added to gases or liquids by letting them flow through the
porous structure and cooling or heating the foam at the same time [10].
While in biomedical application, metal foam has been applied for
orthopaedics and dental implants. Metal foam gives advantages in porosity, strength
and appearance very similar to cancellous bone. By modifying some mechanical
properties of solid metal into metal foam, metal can have similar characteristics with
the bone which can replace the bone and prevent stress shielding [9, 11].
2.1
BIOMEDICAL APPLICATION OF METAL FOAM
The fabrication of porous materials has been actively researched since 1943,
when B. Sosnik attempted to introduce pores into aluminium by adding mercury to
the melt. In 1972, Weber and White have introduced the concept of porous metal in
the biomedical application for osseointegration. Numerous investigations into porous
materials where subsequently initiated in the early 1970’s involving porous ceramic,
polymeric and metallic materials which showed in animal studies to be potential
candidates for porous implants that would enable bone ingrowth [11].
7
2.1.1
Mechanical Properties of Cancellous Bone
Bone is an open cell composite material composed of a complex vascular
system and a significant fraction of protein-related materials. Bone contains two
types of different tissues tightly packed together. The outer shell is called cortical
bone, while the inner core is comprised of porous cellular which called cancellous or
trabecular bone [12]. Figure 2.1 shows the structure of femur.
Figure 2.1:
Cancellous bone and cortical bone [13]
Cancellous bone is the spongy type of bone, which is found in vertebral
bodies and femoral head as in Figure 2.2. The porous space left free by the bone
material is filled with marrow and living cells. Cancellous bone is highly porous,
consisting of an interconnected and loose network of trabeculae which is in the range
about 50 – 300 μm in diameter. The typical thickness of the trabeculae is having a
size of approximately 200 μm in diameter with an orientation that depends on the
load distribution in the bone. Cancellous bone has the porosity ranges between 75%
and 90%. It can be considered as foam like network of bone trabeculae [12, 14].
8
Figure 2.2:
The vertebra and the end of femur are filled with a spongy
structure called cancellous bone [14]
Cancellous bone gives supporting strength to the ends of the weight-bearing
bone. Figure 2.3 shows x-ray of a femur which the thick cortical bone and the
trabecular bone are shown. The bone arrangement is to withstand the stresses from
usual standing and walking. Compressive stresses happen when weight pushing the
bone down while tensile stresses happen when the muscles pulling the bone apart [2,
13]. The mechanical properties of cancellous bone are shown in Table 2.1 [15].
Figure 2.3:
X-ray femur which shows cortical bone and cancellous bone [13]
“I hereby declare that I have read this thesis and in my opinion this thesis is
sufficient in terms of scope and quality for the award of the degree of Bachelor of
Mechanical Engineering (Structure and Materials)”
Signature
:
Supervisor
: DR. MOHD ZULKEFLI BIN SELAMAT
Date
:
EFFECT OF YEAST CONTENT AS FOAMING AGENT ON THE
MECHANICAL PROPERTIES OF TITANIUM FOAM
NURUL FARHANA IZZATI BINTI MOHAMAD NAZRI
This thesis is submitted in partial fulfillment of the requirement for the award
of Bachelor of Mechanical Engineering (Structure and Materials) (HONS.)
Faculty of Mechanical Engineering
Universiti Teknikal Malaysia Melaka
JUNE 2015
iii
DECLARATION
“I hereby declare that the work in this thesis is my own except for summaries and
quotations which have been duly acknowledged.”
Signature
:
Author
: NURUL FARHANA IZZATI BINTI MOHAMAD NAZRI
Date
:
iv
Dedicated to my family
especially for my mother and father
v
ACKNOWLEDGEMENT
I would like to take this opportunity to express my greatest gratitude to the
people who have been instrumental in the successful completion of this Final Year
Project. This project would not been possible without the support of them.
I wish my deepest thanks and appreciate to my final year project supervisor,
Dr Mohd Zulkefli bin Selamat, who was abundantly helpful and offered invaluable
assistance, support and guidance. Without his encouragement and guidance, this
project would not have materialized. Thanks also to the lecturers and lab assistants
who had guide me to complete this project. I warmly thank to my friends for their
valuable advice and friendly help. Last but not least, I wish to express my love and
gratitude to my beloved families for their understanding and endless love through the
duration of my studies.
Without helps of the particular that mentioned above, I would face many
difficulties in completing this project.
vi
ABSTRACT
Nowadays, metal foam has gained interest in industry and became so popular. Its
physical and mechanical properties are believed to give various benefits to various
industries such as automotive, aerospace and biomedical application. Mechanical
properties of metal foam such as light-weight structure, energy absorption, high
stiffness and low Young’s modulus has entrusted the researchers to study the nature
of the metal foam deeper for future benefits. This research succeed to achieve the
research objectives which is to determine the effect of yeast content on the
mechanical properties of titanium foam and study the effect of yeast content on the
size of micro pores. Yeast as new organic foaming agent is proved as a replacement
for existing foaming agent. Yeast weight percentage that have been used are 15, 25
and 30 wt. %. Titanium foam was made up with slurry technique with yeast as
foaming agent and ethylene glycol as binder. The yeast decomposed during the
sintering process and thus, it is environmental friendly. Different ratio of titanium
powder to yeast was used to obtain the best result of titanium foam. The
microstructure of the titanium foam was analysed using inverter microscope and
image analyser was used to obtain the details of microstructure of titanium foam
result. The pore size of titanium foam obtained was in range of 395.63 to 546.78 µm
while the strut size obtained was in the range of 223.13 to 300 µm. The porosities of
titanium foam lead to 60.5 until 75.5%. Furthermore, mechanical testing such as
compression test was carried out. From the compression stress held, Young’s
Modulus can be known. Compression stress of 2.41 to 4.56MPa and Young’s
Modulus of 0.218 to 0.267GPa were obtained. All the results obtained fulfil the
requirements of human cancellous bone.
vii
ABSTRAK
Pada masa kini, logam berbusa telah mendapat tarikan daripada industri dan menjadi
begitu popular. Sifat-sifat fizikal dan mekanikal yang dipercayai memberi pelbagai
manfaat untuk pelbagai industri seperti aplikasi pada automotif, aeroangkasa dan
bioperubatan. Sifat mekanikal logam berbusa seperti struktur ringan, penyerapan
tenaga, kekakuan tinggi dan modulus Young yang rendah telah memberi
kepercayaan pada para penyelidik untuk mengkaji sifat logam berbusa dengan lebih
mendalam untuk faedah masa depan. Kajian ini berjaya mencapai objektif kajian
iaitu untuk menentukan kesan kandungan yis pada sifat-sifat mekanikal titanium
berbusa dan mengkaji kesan kandungan yis kepada saiz liang mikro. Yis sebagai ejen
berbuih organik baru terbukti boleh digunakan untuk menggantikan ejen berbuih
sedia ada dan peratusan berat yis telah digunakan adalah 15, 25 dan 30%. Busa
titanium dibuat dengan teknik buburan dengan yis sebagai ejen berbuih dan etilena
glikol sebagai pengikat. Yis mengurai semasa proses pensinteran dan dengan itu, ia
adalah mesra alam sekitar. Nisbah serbuk titanium kepada yis yang berbeza akan
digunakan untuk mendapatkan hasil titanium berbusa yang terbaik. Mikrostruktur
titanium berbusa telah dianalisis dengan menggunakan inverter mikroskop dan
penganalisis imej telah digunakan untuk mendapatkan butir-butir mikrostruktur hasil
titanium berbusa. Saiz liang busa titanium diperolehi ialah dalam julat 395.63-546.78
µm manakala saiz tupang yang diperolehi adalah dalam julat 223.13-300 µm.
Keporosan busa titanium yang diperolehi adalah antara 60.5 sehingga 75.5%.
Tambahan pula, ujian mekanikal seperti kekuatan mampatan telah dijalankan.
Daripada ujian tekanan mampatan yang dijalankan, Modulus Young dapat diketahui.
Tekanan mampatan bernilai 2.41 hingga 4.56MPa dan Modulus Young bernilai
0.218 hingga 0.267GPa telah diperolehi. Semua keputusan penyelidikan yang
diperolehi memenuhi keperluan tulang cancellous manusia.
viii
TABLE OF CONTENT
CHAPTER
TITLE
PAGES
SUPERVISOR DECLARATION
i
STUDENT DECLARATION
iii
DEDICATION
iv
ACKNOWLEDGMENT
v
ABSTRACT
vi
ABSTRAK
vii
TABLE OF CONTENT
viii
LIST OF TABLES
xi
LIST OF FIGURES
xii
LIST OF SYMBOLS
xv
LIST OF APPENDDICES
xvi
ix
CHAPTER 1 INTRODUCTION
1
1.0
Introduction
1
1.1
Project Objectives
3
1.2
Problem Statement
3
1.3
Project Scope
4
CHAPTER 2 LITERATURE REVIEW
5
2.0
Introduction
5
2.1
Biomedical Application of Metal Foam
6
2.1.1
Mechanical Properties of Cancellous Bone
7
2.1.2
Porosity in Bone Implant
9
2.2
2.3
2.4
2.5
2.6
Material Selection
12
2.2.1
Properties of Titanium
13
2.2.2
Mechanism of Yeast
14
Metal Foams from Metal Powder
15
2.3.1
Sintering of Metal Powders and Fibres
15
2.3.2
Sintering of Hollow Spheres
16
2.3.3
Gas Entrapment
17
2.3.4
Foaming of Slurries
18
2.3.5
The Addition of Space-holding Fillers
18
2.3.6
Extrusion of Metal Mixtures
19
Mechanical Testing of Titanium Foam
20
2.4.1
Compression Test
20
2.4.2
Hardness Test
21
Characterisation of Pore
22
2.5.1
Pore Microstructure
22
2.5.2
Density
23
Research Focus
23
x
CHAPTER 3 METHODOLOGY
24
3.0
Introduction
24
3.1
Fabrication Process
24
3.2
Raw Material
26
3.3
Development of Porous Titanium Specimen
by Sintering Process
29
3.4
Mechanical Testing
31
3.5
Characterisation of Titanium Foam Microstructure
32
CHAPTER 4 RESULTS AND ANALYSIS
34
4.1
Introduction
34
4.2
Microstructure Analysis of Titanium Foam
34
4.2.1
Result
35
Porosity and Density
37
4.3.1
37
4.3
4.4
Result
Compression Test and Young’s Modulus
39
4.4.1
39
Result
CHAPTER 5 DISCUSSION
41
5.1
Microstructure of Titanium Foam
41
5.2
Porosity and Density
42
5.3
Compression Strength and Young’s Modulus
43
5.4
Comparison between Cancellous Bone and Titanium
Foam
45
CHAPTER 6 CONCLUSION
46
6.1
Conclusion
46
6.2
Recommendations
47
REFERENCES
48
APPENDIX
52
xi
LIST OF TABLES
NO
TITLE
2.1
The mechanical properties of cancellous bone
2.2
The mechanical properties of metals used in orthopaedic
PAGES
9
application
14
3.1
Properties of titanium powder
26
3.2
Properties of yeast
27
3.3
Composition of titanium powder and yeast
27
3.4
Titanium foam ready to be put in the furnace
29
4.1
Average pore size and strut size of titanium foam
35
4.2
Microstructure of titanium foam
36
4.3
Average density and porosity of titanium foam
37
4.4
Average compressive stress and Young’s Modulus of titanium
foam
5.1
39
The comparison between present research, human cancellous bone
and fabricated titanium foam from other research
45
xii
LIST OF FIGURES
NO
TITLE
2.1
Cancellous bone and cortical bone
2.2
The vertebra and the end of femur are filled with a
PAGES
7
spongy structure called cancellous bone
8
2.3
X-ray femur which shows cortical bone and cancellous bone
8
2.4
X-ray of: (1A) Normal healthy hip, (1B) Total hip replacement
10
2.5
Bone ingrowth into the pores ensure stable fixation
10
2.6
Figure 2.6 (a) Normal stresses flow in human body weight,
(b) Stress shielding occurs at the implant area
11
2.7
Styrofoam coating process for making hollow sphere structures
16
2.8
Gas Entrapment technique
17
2.9
Schematic illustration of the production of the titanium foams
18
2.10
The schematic process of space-holder technique
19
2.11
Process for making cellular metals with oriented porosity
from metal powders
20
xiii
2.12
Stress-strain graph of an orthopaedic titanium alloy tested
in tension
21
3.1
Flow chart of slurry technique in the research
25
3.2
Titanium powder (Ti6 – Al4– V)
26
3.3
Yeast
27
3.4
PVC pipe mould
28
3.5
Titanium slurry in the mould at room temperature
28
3.6
Vacuum furnace
30
3.7
Sintering cycle for the preparation of the titanium foam
30
3.8
Compression testing on titanium foam sample
31
3.9
Universal Testing Machine Instron 5585
31
3.10
Grinding and Polishing Machine
32
3.11
Samples in mounting cup
32
3.12
Inverter Microscope
33
3.13
Electronic densimeter
33
4.1
Pore morphology of fabricated titanium foam at 85% titanium
weight composition to 15% yeast weight composition.
4.2
Pore morphology of fabricated titanium foam at 75% titanium
weight composition to 25% yeast weight composition.
4.3
36
36
Pore morphology of fabricated titanium foam at 70% titanium
weight composition to 30% yeast weight composition.
36
4.4
Effect of Yeast Weight Composition to Density
38
4.5
Effect of Yeast Weight Composition to Porosity
38
xiv
4.6
Effect of Yeast Weight Composition to Compression stress
and Young’s Modulus
5.1
Effect of different yeast weight composition to pore size
and strut size
5.2
40
42
The effect of porosity to compressive stress and Young’s
Modulus of fabricated titanium foam
44
xv
LIST OF SYMBOLS
*
s
= density of foam
= density of solid material
= porosity
= volume of pore space
= total volume of sample
xvi
LIST OF APPENDICES
NO
TITLE
PAGES
1
Gantt Chart PSM I
53
2
Gantt Chart PSM II
54
3
The results of the pore size and strut size for titanium foam
4
The test results of density for titanium foam
56
5
Graph of compression test
57
55
CHAPTER 1
INTRODUCTION
1.0
BACKGROUND
Porous materials are easy to be found in the natural structure such as cork,
wood, bone and sponge. All of these natural structures have a great structural
strength yet lightweight. Therefore, man has applied this natural condition to the
man-made porous material from metal and ceramics. Those made have been widely
exploited because of the unique combination of physical and mechanical properties
offered by porous metals [1].
The characteristic of metallic foam is a combination of properties of metal
and foam. Metal foam is a gas bubble-filled substance made out of metal. It is a
structural material that contains a high volume of porosity within a metal and
typically very lightweight due to the low density [2]. Metal foam has been widely
used around the world involving aerospace, automotive, structural and biomedical.
Their applications are still promising and perspective even it had been introduced
over half of the centuries. It gives many beneficial in term of mechanical properties,
for
2
instance, high impact energy absorption, high stiffness, high strength to weight
ratios, high gas permeability, and high thermal conductivity [2].
The physics of metal foaming contains five stages which are making the
precursor, initial pore formation, pore inflation, foam degradation and solidification.
Mixture of metal powder and gas-releasing foaming agent is compacted to make the
precursor. While the precursor is on heating, gas evolves in the precursor and process
of pore formation begins to start. Pore formation is continually enlarged as the
foaming agent is decomposed. The ongoing gas supply from the decomposition of
foaming agent boosts the pore formation. Degradation begins while pores are being
inflated. Drainage occurs due to the downward flow of liquid through Plateau border
under gravity and bubbles coalesce as films become thin and unstable. The metal has
to be solidified quickly at the right time to prevent this unstable foam from collapse.
Deformation of films or crack may occur in the cell walls due to sudden
solidification [2].
The pore characteristics are divided into pore morphology, porosity and pore
size. Pore morphology is divided into open and closed pores. The difference between
both of it is in term of permeability where fluid can penetrate. Open pores are
penetrating pores while closed pores are non-penetrating. Open pores are very
important for separation-filtration while closed pores are beneficial for light-weight
materials and heat insulating materials [3].
The porosity means the fraction of pore volume to the total volume. Higher
porosity leads to lower Young Modulus. Thus, metal foam with smaller pores
generally has better elastic of modulus than metal foam with larger pores at an
equivalent porosity. Range of porosity will also influence thermal and electrical
conductivity, thermal shock resistance and gas permeability besides mechanical
properties [3].
3
1.1
PROJECT OBJECTIVES
The objectives of this research is to determine the effect of yeast content on
the mechanical properties of titanium foam and study the effect of yeast content on
the size of micro pores.
1.2
PROBLEM STATEMENT
Nowadays, use of titanium in biomedical application became so attractive and
popular due to its great corrosion resistance, biocompatibility and high strength to
weight ratio. However, elastic modulus of titanium, which is 110.3 GPa, is too high
compared to elastic modulus of human bone, which is in the ranges of 0.09–1.5 GPa
while for its compressive yield strength is 40–150 MPa [4]. This condition may lead
to stress shielding to the bone. Stress shielding is occurred due to the mismatch of
Young’s Modulus between the bone and metallic implants [5].
Hence, porous titanium is introduced to reduce the Young’s modulus and
thus, increased the productivity of titanium use in biomedical application. In this
research, a method of titanium foam preparation with yeast as foaming agent is
introduced and its mechanical properties in term of Young modulus and strength is
investigated; thus, study size of micro pores affected by yeast content. Heat causes
yeast to decompose and release gas, which then propels the foaming process. The
porous titanium had been fabricated using mixture of yeast and titanium powder by
controlling the ratio of yeast to titanium powder [6]. The mechanical properties and
pore structure of titanium foam obtained from this research could be mimicking to
those of the human bone.
4
1.3
PROJECT SCOPE
This research studied about the effect of yeast content as pore foaming agent
on the micro pores and mechanical properties of titanium foam as macro-porous
materials. In this research, the method used to prepare titanium foam is slurry
method. Titanium foam was being produced by preparing slurry of titanium powders
mixed with yeast as foaming agent. Preparation of slurry had started by mixing up of
yeast with titanium powder and ethylene glycol as binder. Certain amount of distilled
water was added to the mixture of titanium powder, yeast and binder for stir mixing.
Then, the slurry was mixed until the compounds were distributed evenly. After that,
the slurry was poured into the PVC mold and allowed it to dry under the room
temperature. The process was followed by sintering process with the temperature of
1250oC for 2 hours and with sintering rate of 5oC/min.
Different ratio of yeast to titanium powder was the processing parameter that
should be taken care during production of titanium foam to achieve these objectives.
This research investigated the suitability of production of titanium foam from the
mixture of titanium powder and yeast through slurry method. In determining the
mechanical properties, the compressive test had been carried out, the microstructures
of sintered porous materials were observed and the pores sizes were measured. The
mechanical properties and pore structure of titanium foam were investigated to
ensure it was closely resemble those of the human bone.
CHAPTER 2
LITERATURE REVIEW
2.0
INTRODUCTION
In 8 May 1943, Benjamin Sosnick is the person who had invented metal
foam. He had filed a patent entitled “Process for making Foam like Mass of Metal”.
He first melted a mix of 90 parts of aluminium, Al, to 10 parts of mercury, Hg, in a
closed chamber or under conditions to prevent the mercury vapour to escape. When
Hg in the mixture is stabilized, the pressure was released. This led to volatilizing of
Hg in the mass and thus, foam was formed [2, 7].
Nowadays, the application of metal foam becomes so popular and plays an
important role in industries due to its advantages. It is applied in a wide range of
sectors and industries which include transportation, defense, architecture, aviation,
marine, energy and process industries.
Metal foam is introduced to improve crash energy absorption at crash boxes
and bumper beams in the automotive industry. Besides, in Korea, some foam has
also been deployed in muffler system to reduce noise compared to regular muffler[8].
6
In aerospace, metal foam structural parts are being considered for turbine
component and as reinforcement for load bearing structures in satellites. Boeing also
had evaluated the use of large aluminium and titanium foam sandwich parts for tail
booms of helicopter [8]. The application of metal foams in railway is concerning
lightweight construction, energy absorption and damping insulation. In Japan, to
improve crash energy absorption, the trains has been fitted out with a 2.3 m3 block of
“Alporas” foam [9].
Moreover, open porosity metal foam also is applied as heat exchanger. Heat
can be removed from or added to gases or liquids by letting them flow through the
porous structure and cooling or heating the foam at the same time [10].
While in biomedical application, metal foam has been applied for
orthopaedics and dental implants. Metal foam gives advantages in porosity, strength
and appearance very similar to cancellous bone. By modifying some mechanical
properties of solid metal into metal foam, metal can have similar characteristics with
the bone which can replace the bone and prevent stress shielding [9, 11].
2.1
BIOMEDICAL APPLICATION OF METAL FOAM
The fabrication of porous materials has been actively researched since 1943,
when B. Sosnik attempted to introduce pores into aluminium by adding mercury to
the melt. In 1972, Weber and White have introduced the concept of porous metal in
the biomedical application for osseointegration. Numerous investigations into porous
materials where subsequently initiated in the early 1970’s involving porous ceramic,
polymeric and metallic materials which showed in animal studies to be potential
candidates for porous implants that would enable bone ingrowth [11].
7
2.1.1
Mechanical Properties of Cancellous Bone
Bone is an open cell composite material composed of a complex vascular
system and a significant fraction of protein-related materials. Bone contains two
types of different tissues tightly packed together. The outer shell is called cortical
bone, while the inner core is comprised of porous cellular which called cancellous or
trabecular bone [12]. Figure 2.1 shows the structure of femur.
Figure 2.1:
Cancellous bone and cortical bone [13]
Cancellous bone is the spongy type of bone, which is found in vertebral
bodies and femoral head as in Figure 2.2. The porous space left free by the bone
material is filled with marrow and living cells. Cancellous bone is highly porous,
consisting of an interconnected and loose network of trabeculae which is in the range
about 50 – 300 μm in diameter. The typical thickness of the trabeculae is having a
size of approximately 200 μm in diameter with an orientation that depends on the
load distribution in the bone. Cancellous bone has the porosity ranges between 75%
and 90%. It can be considered as foam like network of bone trabeculae [12, 14].
8
Figure 2.2:
The vertebra and the end of femur are filled with a spongy
structure called cancellous bone [14]
Cancellous bone gives supporting strength to the ends of the weight-bearing
bone. Figure 2.3 shows x-ray of a femur which the thick cortical bone and the
trabecular bone are shown. The bone arrangement is to withstand the stresses from
usual standing and walking. Compressive stresses happen when weight pushing the
bone down while tensile stresses happen when the muscles pulling the bone apart [2,
13]. The mechanical properties of cancellous bone are shown in Table 2.1 [15].
Figure 2.3:
X-ray femur which shows cortical bone and cancellous bone [13]