Surface Treatment of Titanium and its Alloys for Adhesion Promotion

283 Pages·2015·16.28 MB·English

Surface Treatment of Titanium and
its Alloys for Adhesion Promotion

A Thesis Submitted to the University of Manchester for the
Degree of Doctor of Philosophy
in the Faculty of Engineering and Physical Sciences

2015

ZUOJIA LIU

Corrosion and Protection Centre
School of Materials
List of Contents

List of Contents

List of Contents ........................................................................................................................ 2
List of Tables ........................................................................................................................... 7
List of Figures .......................................................................................................................... 8
List of Abbreviations ............................................................................................................. 14
Abstract .................................................................................................................................. 15
Declaration ............................................................................................................................. 18
Zuojia Liu .............................................................................................................................. 18
Copyright Statement .............................................................................................................. 19
Acknowledgements ................................................................................................................ 21
Chapter 1 Introduction ........................................................................................................ 22
1.1. Background……………………………………………………………………….22
1.2. Research Objectives………………………………………………………………27
1.3. Layout of Thesis………………………………………………………………….28
Chapter 2 Literature Review .............................................................................................. 30
2.2. Properties of Titanium and Its Alloys…………………………………………….30
2.2.1. α – Alloy ........................................................................................................ 31
2.2.2. α + β Alloy ..................................................................................................... 32
2.2.3. β – Alloy ........................................................................................................ 37
2.2.4. Titanium Dioxide ........................................................................................... 38
2.3. Anodizing of Titanium……………………………………………………………40
2.3.1. Barrier-type Anodic Film ............................................................................... 42
2.3.2. Porous-type Anodic Film ............................................................................... 47
2.3.3. Oxygen Evolution during Anodizing ............................................................. 50
2.4. Overview of Adhesion Techniques……………………………………………….53
2.4.1. Single-Lap Shear Test .................................................................................... 53
2.4.2. Tensile Test .................................................................................................... 54
2.4.3. Wedge Test .................................................................................................... 54
2.4.4. Cross-cut Test ................................................................................................ 55
Chapter 3 Experimental Methods and Procedures ............................................................. 57
3.1. Introduction……………………………………………………………………….57
3.2. Barrier Anodic Oxide Film Growth of CP-Titanium in Sulphuric and Phosphoric
Acids……………………………………………………………………………………...57
3.2.1. Material and Pre-Treatments .......................................................................... 57
3.2.2. Anodizing ....................................................................................................... 57
3.2.3. Scanning & Transmission Electron Microscopes .......................................... 58
3.2.4. Focused-ion Beam ......................................................................................... 58
3.2.5. X-ray Diffraction ........................................................................................... 59
2
List of Contents

3.2.6. Glow Discharge Optical Emission Spectroscopy .......................................... 59
3.2.7. X-ray Photoelectron Spectroscopy................................................................. 59
3.2.8. Electrochemical Impedance Spectroscopy ..................................................... 59
3.2.9. Rutherford Backscattering Spectroscopy / Nuclear Reaction Analysis ......... 60
3.3. Corrosion Behaviour of Anodic Oxide Film on CP-Titanium in NaCl
environment………………………………………………………………………………60
3.3.1. Material and Anodizing ................................................................................. 60
3.3.2. Electrochemical Measurements ..................................................................... 61
3.3.3. Morphology Characterization ........................................................................ 61
3.4. Formation of Porous Anodic Oxide Film On CP-Titanium in Phosphoric Acid
Electrolyte………………………………………………………………………………...62
3.4.1. Material and Anodizing ................................................................................. 62
3.4.2. Scanning Electron Microscopy ...................................................................... 62
3.4.3. Raman Spectroscopy ...................................................................................... 62
3.4.4. Electrochemical Impedance Spectroscopy ..................................................... 63
3.4.5. Glow Discharge Optical Emission Spectroscopy .......................................... 63
3.5. Characterization of Anodic Oxide Growth on CP-Titanium in NaTESi electrolyte
with Associated Degradation and Adhesive Bonding Behaviours……………………….63
3.5.1. Material and Anodizing ................................................................................. 63
3.5.2. Scanning & Transmission Electron Microscopes .......................................... 64
3.5.3. Raman Spectroscopy ...................................................................................... 64
3.5.4. Glow Discharge Optical Emission Spectroscopy .......................................... 64
3.5.5. Rutherford Backscattering Spectroscopy / Nuclear Reaction Analysis ......... 64
3.5.6. Electrochemical Impedance Spectroscopy ..................................................... 65
3.5.7. Degradation Test ............................................................................................ 65
3.5.8. Single-lap Shear Test ..................................................................................... 65
Figure 3.2. Schematic representation of the single-lap shear test of titanium materials. ....... 66
3.6. Characterization of Anodic Oxide Growth on Ti6Al4V Alloy in NaTESi
electrolyte with Associated Degradation and Adhesive Bonding Behaviours…………...66
3.6.1. Material and Anodizing ................................................................................. 66
3.6.2. Degradation Test ............................................................................................ 67
3.6.3. Single-lap Shear Test ..................................................................................... 67
3.6.4. Techniques for Characterization .................................................................... 67
3.7. Anodic Oxide Film Growth on Magnetron Sputter-Deposited Titanium………...68
3.7.1. Material and Sputtering .................................................................................. 68
3.7.2. Anodizing ....................................................................................................... 69
3.7.3. Scanning & Transmission Electron Microscopes .......................................... 69
3.7.4. Glow Discharge Optical Emission Spectroscopy .......................................... 70
3.8. Scanning Transmission Electron Microscopy Technique in Scanning Electron
Microscopy for Morphology Analysis of Anodic Oxide Film Formed on Titanium…….70
3.8.1. Instrument ...................................................................................................... 70
3
List of Contents

3.8.2. Materials and Anodizing ................................................................................ 72
3.8.3. Ultramicrotomy .............................................................................................. 72
Chapter 4 Barrier Anodic Oxide Film Growth of CP-Titanium in Sulphuric and Phosphoric
Acids ...................................................................................................................................... 75
4.1. Introduction……………………………………………………………………….75
4.2. Pre-Treated Surfaces of CP-Ti……………………………………………………75
4.3. Anodizing and Film Characterizations…………………………………………...76
4.2.1. Potentiodynamic Polarization and Current-Time Responses ......................... 76
4.2.2. Interference Colours ....................................................................................... 77
4.2.3. Microstructure of Anodic Films ..................................................................... 77
4.2.4. X-ray Diffraction Patterns .............................................................................. 78
4.2.5. Rutherford Backscattering Spectroscopy & Nuclear Reaction Analysis ....... 78
4.2.6. Glow Discharge Optical Emission Spectroscopy .......................................... 80
4.2.7. X-ray Photoelectron Spectroscopy................................................................. 80
4.2.8. Electrochemical Impedance Spectroscopy ..................................................... 81
4.4. Discussion………………………………………………………………………...82
4.5. Summary………………………………………………………………………….84
Chapter 5 Corrosion Behaviour of Anodic Oxide Film on CP-Titanium in NaCl
Environment......................................................................................................................... 102
5.1. Introduction……………………………………………………………………...102
5.2. Voltage-Time Responses………………………………………………………..102
5.3. Scanning Electron Microscopy………………………………………………….103
5.4. Electrochemical Impedance Spectroscopy……………………………………...104
5.5. Potentiodynamic Polarization Measurements…………………………………...106
5.6. Discussion……………………………………………………………………….108
5.7. Summary………………………………………………………………………...110
Chapter 6 Formation of Porous Anodic Oxide Film on CP-Titanium in Phosphoric Acid
Electrolyte ............................................................................................................................ 118
6.1. Introduction……………………………………………………………………...118
6.2. Current – Time Responses………………………………………………………118
6.3. Film Morphology………………………………………………………………..119
6.4. Compositions of Anodic Films………………………………………………….120
6.5. Crystallization Behaviour……………………………………………………….121
6.6. Dielectric Properties……………………………………………………………..122
6.7. Discussion……………………………………………………………………….123
6.8. Summary………………………………………………………………………...124
Chapter 7 Characterization of Anodic Oxide Growth on CP-Titanium in NaTESi
electrolyte with Associated Degradation and Adhesive Bonding Behaviours ..................... 133
7.1. Introduction……………………………………………………………………...133
7.2. Voltage – Time Response……………………………………………………….133
4
List of Contents

7.3. Scanning Electron Microscopy………………………………………………….133
7.4. Raman Spectroscopy…………………………………………………………….134
7.5. Transmission Electron Microscopy……………………………………………..134
7.6. Glow Discharge Optical Emission Spectroscopy……………………………….135
7.7. Rutherford Backscattering Spectroscopy / Nuclear Reaction Analysis…………135
7.8. Electrochemical Impedance Spectroscopy……………………………………...136
7.9. Degradation and Single-lap Shear Tests………………………………………...137
7.9.1. Surface Morphology after Degradation ....................................................... 137
7.9.2. Load – Displacement Responses.................................................................. 138
7.9.3. Surface Morphology after Shear Bonding ................................................... 138
7.10. Discussion……………………………………………………………………….139
7.11. Summary………………………………………………………………………...142
Chapter 8 Characterization of Anodic Oxide Growth on Ti6Al4V Alloy in NaTESi
electrolyte with Associated Degradation and Adhesive Bonding Behaviours ..................... 156
8.1. Introduction……………………………………………………………………...156
8.2. Ti6Al4V Pre-Treated Alloy……………………………………………………..156
8.3. Voltage - Time Response……………………………………………………….157
8.4. Morphology of Anodic Oxide Films…………………………………………….157
8.5. Crystalline Structures of Anodic Films………………………………………….158
8.5.1. Raman Spectra ............................................................................................. 158
8.5.2. Transmission Electron Microscopy ............................................................. 158
8.6. Film Compositions………………………………………………………………159
8.6.1. Glow Discharge Optical Emission Spectroscopy ........................................ 159
8.6.2. Rutherford Backscattering Spectroscopy / Nuclear Reaction Analysis ....... 159
8.7. Dielectric Properties of Anodic Films…………………………………………..160
8.8. Degradation and Single-lap Shear Tests………………………………………...162
8.8.1. Surface Morphology after Degradation ....................................................... 162
8.8.2. Load – Displacement Responses.................................................................. 163
8.8.3. Surface Morphology after Shear Bonding ................................................... 163
8.9. Discussion……………………………………………………………………….164
8.10. Summary………………………………………………………………………...168
Chapter 9 Anodic Oxide Film Growth on Magnetron Sputter-Deposited Titanium........ 187
9.1. Introduction……………………………………………………………………...187
9.2. Sputter-Deposited Titanium Layer……………………………………………...187
9.3. Anodizing of ~100 nm Thick Sputter-Deposited Titanium……………………..188
9.4. Anodizing of ~290 nm Thick Sputter-Deposited Titanium……………………..190
9.5. Discussion……………………………………………………………………….191
9.6. Summary………………………………………………………………………...192
Chapter 10 Scanning Transmission Electron Microscopy Technique in Scanning Electron
Microscopy for Morphology Analysis of the Anodic Oxide Film Formed on Titanium ..... 204
5
List of Contents

10.1. Introduction……………………………………………………………………...204
10.2. Anodic Films formed on Sputter-Deposited Ti…………………………………204
10.3. Other Use of STEM-in-SEM……………………………………………………205
10.2. Discussion……………………………………………………………………….206
10.3. Summary………………………………………………………………………...207
Chapter 11 Chemical Etching Behaviour of CP-Titanium in Bromine-Methanol Electrolyte
............................................................................................................................................. 212
11.1. Introduction……………………………………………………………………...212
11.3. Titanium before and after Etching………………………………………………213
11.4. Discussion……………………………………………………………………….216
11.5. Summary………………………………………………………………………...218
Chapter 12 Main Conclusions and Suggestions for Future Work..................................... 227
12.1. Main Conclusions……………………………………………………………….227
12.2. Suggestions for Future Work……………………………………………………233
References ............................................................................................................................ 236
Appendices........................................................................................................................... 243
List of Publications .............................................................................................................. 243

The word count: 55,900
6
List of Tables

List of Tables

Table 2.1. Chemical compositions (wt%) of cp-titanium Grade 1 – 4 [22] .......................... 31
Table 2.2. Chemical compositions of the as-received and heat-treated Ti-6Al-4V alloy
analyzed by EDS (wt%) [37]. ........................................................................................ 37
Table 3.1. Chemical compositions (wt%) of Ti6Al4V alloy sheet used for anodizing,
degradation and adhesive bonding tests. ........................................................................ 67
Table 4.1. Current densities (A cm-2) of cp-titanium after anodizing at different constant
voltages in H SO and H PO electrolytes for 900 s. …………………………………77
2 4 3 4
Table 5.1. The electrochemical impedance spectroscopy parameters of CP-Ti electrode in
different experimental conditions…………………………………………………….106
Table 5.2. The potentiodynamic polarization parameters of CP-Ti electrode in different
experimental conditions. ............................................................................................. .108
Table 6.1. EIS fitted data for anodic films formed on CP-titanium at different voltages...123
Table 7.1. RBS and NRA results of examinations of anodic oxide films on titanium in
NaTESi electrolyte to different anodic voltages……………………………………..136
Table 7.2. EIS fitting results of anodic films formed on titanium after anodizing to different
anodic voltages in NaTESi electrolyte. ........................................................................ 137
Table 7.3. EDS spectra of different regions on anodized titanium after adhesive bonding
tests. ............................................................................................................................. 139
Table 8.1. EDS results of anodic films formed on Ti6Al4V alloy after anodizing to 10, 20,
30 and 40 V in NaTESi electrolyte…………………………………………..............158
Table 8.2. RBS and NRA results of anodized Ti6Al4V alloy to 10, 20, 30 and 40 V in
NaTESi electrolyte. ...................................................................................................... 160
Table 8.3. EIS fitting data obtained from the equivalent circuits of the titanium alloy
anodized to 10, 20, 30 and 40 V respectively in the NaTESi electrolyte. ................... 162
Table 8.4. EDS results of anodized Ti6Al4V alloy after degradation test in a continuous
climatic chamber with a humidity of 90% at 50 oC for 1000 h. ................................... 163
Table 8.5. EDS results of anodized Ti6Al4V alloy after single-lap shear bonding tests
immediately. ................................................................................................................ 164
Table 11.1. Pit depth and surface roughness of titanium after chemical etching in bromine-
methanol electrolyte for different times……………………………………………...216

7
List of Figures

List of Figures
Figure 1.1. Increase in application of titanium alloys in commercial Boeing aircraft [8]. .... 24
Figure 1.2. Percentage of aluminium, titanium, and steel alloys and carbon fibre reinforced
polymer (CFRP) of the structural weight of modern large commercial aircraft and gas
turbine engines [8]. ........................................................................................................ 24
Figure 2.1. The two main crystal structures, hexagonal close packed (HCP) and body centred
cubic (BCC), for the α and β phases of titanium [22, 24]……………………………...30
Figure 2.2. Scanning electron micrograph showing the typical microstructue of CP-Ti: grain
boundary α (A), fine accicular α (B), Widmanstätten α (C) and serrated α (D) [27]. .... 32
Figure 2.3. A schematic illustration of microstructures transformation in Ti-6Al-4V after
quenching at different temperatures [34]. ...................................................................... 34
Figure 2.4. Optical micrograph of the microstructure of Ti6Al4V alloy showing a bi-modal
microstructure consisting of α surrounded by transformed β (530X) [23, 33, 35]. ....... 35
Figure 2.5. Scanning electron micrographs displaying the microstructures of Ti-6Al-4V
alloy: (a) as-received and (b) solution annealed at 1066 oC/1h + furnace cooling [37]. 36
Figure 2.6. Scanning electron micrograph showing typical Ti6Al4V microstructure
containing very fine acicular α (E), fine acicular α and β (F) and prior-β grain
boundaries (G) [27]. ....................................................................................................... 37
Figure 2.7. Optical micrograph showing the microstructure of the as-received Ti-15V-3Cr-
3Sn-3Al (Ti-15-3) alloy [40]. ........................................................................................ 38
Figure 2.8. Schematic diagrams showing the bulk structures of rutile and anatase. The
stacking of the octahedral unit cells in both structures are shown on the right side [44].
....................................................................................................................................... 40
Figure 2.9. Interference between two waves reflected at both surfaces of an oxidised
titanium metal substrate [51]. ........................................................................................ 41
Figure 2.10. Transmission electron micrographs and electron diffraction patterns of the
stripped anodic oxide of pure titanium obtained after anodized at 25V for 60 min [80].
....................................................................................................................................... 44
Figure 2.11. Transmission electron micrograph of an ultramicrotomed section of the sputter
deposited Ti–11.5 at.% Mo alloy anodized to 80 V at a constant current density of 50
mA in a 0.1 mol dm-3 ammonium pentaborate electrolyte at 293K [83]. ...................... 45
Figure 2.12. Transmission electron micrographs of ultramicrotomed sections for the sputter-
deposited (a) Ti–6 at.% Si, (b) Ti–12 at.% Si and (c) Ti–26 at.% Si alloys anodized at
50 A m−2 in 0.1 mol dm−3 ammonium pentaborate electrolyte at 293 K. The formation
voltages are 75 V for Ti–6 at.% Si alloy and 100 V for the Ti–12 at.% Si and Ti–26 at.%
Si alloys. The selected area electron diffraction patterns of the respective alloys are also
shown [84]. .................................................................................................................... 46
Figure 2.13. Transmission electron micrographs showing regions of different porosity in
anodic oxide films formed in H SO at 40 V on α-phase grains of Ti-6A1-4V (bright
2 4
field) [85]. ...................................................................................................................... 47
Figure 2.14. Scanning electron micrographs at top view (a), cross sectional (b), and bottom
view images of titanium oxide nanotubes anodized in 0.5 wt% HF solution at 20 V for
20 min [93]. .................................................................................................................... 48
Figure 2.15. Scanning electron micrographs of anodic oxide films on CP-Ti after anodizing
in 1.4 M H PO for 1 min: 200V (a) and 250V (b) [111]. .............................................. 50
3 4
Figure 2.16. Transmission electron micrograph of an ultramicrotomed section of the
sputtering-deposited titanium anodized to 20 V at 50 A m-2 in 0.1 mol dm-3 ammonium
pentaborate electrolyte at 293 K [120]. .......................................................................... 52
Figure 2.17. Schematic diagram of the specific single-lap joint experimental setup and its
dimensions [125]. ........................................................................................................... 53
8
List of Figures

Figure 2.18. Schematic diagram of a “butt tensile” specimen. Metal rods are used for the
adherends. The surfaces of the metal rods must be smooth and parallel when the bond is
made [127]. .................................................................................................................... 54
Figure 2.19. ASTM D3762 wedge test for assessing bond durability [129]. ......................... 55
Figure 2.20. Principle of classifying paint film adhesion in the cross-cut test [131]. ............ 56
Figure 3.1. Schematic representation of the polarization and anodizing processes in a three-
cell electrochemical system. a) Application of potentiodynamic polarization at the
range from 0 V vs. (Ref) to an anodic voltage vs. (Ref). b) Continued application of the
constant anodic voltage to record the current-time response…………………………..58
Figure 3.2. Schematic representation of the single-lap shear test of titanium materials. ....... 66
Figure 3.3. Schematic representation of thin film deposition using dc sputtering technique in
Argon atmosphere. ......................................................................................................... 69
Figure 3.4. Schematic showing the top view of parts (A), (B) and (C), represent for STEM
detector, detector extension arm and carousel holder. Photo inside the SEM chamber
corresponds to the schematics of the top view. The 6-sample carousel is aligned with
the electron column, and the STEM detector is brought with the detector arm, and the
imagining is ready after the working distance is set for both carousel and STEM
detectors. ........................................................................................................................ 71
Figure 4.1. Scanning electron micrographs at different magnifications of as-received CP-Ti
after GDOES sputter cleaning (a and b) and after etching in 48% HF + 70% HNO (c
3
and d) at ambient temperature………………………………………………………….85
Figure 4.2. Electron backscatter diffraction (EBSD) of CP-Ti after etching in HF + HNO ; a,
3
the mapping area of titanium; b, mapping result; c, inverse pole figures (IPF). ............ 86
Figure 4.3. Potentiodynamic polarization scanning from 0 V (vs. SCE) to 60 V (vs. SCE) in
1 M sulphuric and 1 M phosphoric acids. ...................................................................... 87
Figure 4.4. Time evolution of the current density at different anodic voltages in 1 M
sulphuric acid, (a) in 1 M phosphoric acid (b). .............................................................. 88
Figure 4.5. The colourations of anodic oxide formed on titanium following anodizing in
sulphuric (up) and phosphoric acid (down) at different anodic voltages. The original
photos were cropped to highlight the colours. ............................................................... 89
Figure 4.6. Scanning electron micrographs of the anodic films formed at 10 (a), 20 (b), 30
(c), 40 (d), 50 (e) and 60 (f) V for 900 s in 1 M sulphuric acid. ................................... 90
Figure 4.7. Scanning electron micrographs of the anodic films formed at 10 (a), 20 (b), 30
(c), 40 (d), 50 (e) and 60 (f) V for 900 s in 1 M phosphoric acid. ................................. 91
Figure 4.8. Transmission electron micrographs of the anodic films formed at 50 V for 900 s
in 1 M sulphuric acid (a, b, c) and phosphoric acid (d, e, f) respectively at different
magnifications. ............................................................................................................... 92
Figure 4.9. X-ray diffraction patterns of anodic films formed at 10 V, 30 V and 50 V in
sulphuric acid (a) and phosphoric acid (b) for 900 s. ..................................................... 93
Figure 4.10. RBS spectra with fitted curves for the anodic film formed at 20 (a) and 50 (b) V
respectively in 1 M H SO electrolyte. .......................................................................... 94
2 4
Figure 4.11. RBS spectra with fitted curves for the anodic film formed at 20 (a) and 50 (b) V
respectively in 1 M H PO electrolyte. .......................................................................... 95
3 4
Figure 4.12. NRA spectra of anodic film formed at 20 (a) and 50 (b) V in 1 M H SO
2 4
electrolyte. ...................................................................................................................... 96
Figure 4.13. NRA spectra of anodic film formed at 20 (a) and 50 (b) V in 1 M H PO
3 4
electrolyte. ...................................................................................................................... 96
Figure 4.14. GDOES depth profiling analysis of anodic film formed in sulphuric acid and
phosphoric acid at 10 V (a and c) and 50 V (b and d). .................................................. 98
Figure 4.15. High resolution XPS spectra of anodic films formed at 50 V in sulphuric acid
and phosphoric acid electrolytes respectively. (a) Ti2p peak; (b) O1s peak, (c) C1s peak,
(d) S2p peak from sulphuric acid and (e) P2p peak from phosphoric acid. ................... 99
Figure 4.16. Bode plots as a function of voltages, and Nyquist diagrams in sulphuric acid (a,
b and c) and phosphoric acid (d, e and f). .................................................................... 100
9
List of Figures

Figure 4.17. Relationship between film thicknesses and voltages in sulphuric and phosphoric
acids. ............................................................................................................................ 101
Figure 5.1. Voltage-time responses during anodizing of CP-Ti in 1 M H SO (a) and 1 M
2 4
H PO (b) electrolytes at 20 mA cm-2 respectively at ambient temperature………….111
3 4
Figure 5.2. Scanning electron micrographs of titanium after etching in HF+HNO , and
3
anodic films formed at 20 mA cm-2 to different voltages in 1 M H SO and 1 M H PO
2 4 3 4
electrolytes respectively: (a) etched titanium; anodizing in H SO to (b) 20 V; (c) 40 V
2 4
and (d) 60 V; anodizing in H PO to (e) 20 V; (f) 40 V and (g) 60 V. ........................ 112
3 4
Figure 5.3. Scanning electron micrographs of titanium after etching, and anodized at 20 mA
cm-2 to different voltages in 1 M H SO and 1 M H PO electrolytes respectively
2 4 3 4
followed by immersion for 60 days in naturally aerated 3.5% NaCl electrolyte; (a)
etched titanium; anodized in H SO to (b) 20 V; (c) 40 V and (d) 60 V; anodized in
2 4
H PO to (e) 20 V; (f) 40 V and (g) 60 V. ................................................................... 113
3 4
Figure 5.4. Bode plots of the etched titanium after immediate immersion, and after
immersion for 60 days in naturally aerated 3.5% NaCl electrolyte. ............................ 114
Figure 5.5. Bode plots of titanium anodized in 1 M H SO to 20, 40 and 60 V respectively,
2 4
and followed by immersion for 60 days in naturally aerated 3.5% NaCl electrolyte. . 114
Figure 5.6. Bode plots of titanium anodized in 1 M H PO to 20, 40 and 60 V respectively,
3 4
and followed by immersion for 60 days in naturally aerated 3.5% NaCl electrolyte. . 115
Figure 5.7. Equivalent circuit for the monitoring of the impedance spectra. R , C and R , as
s o o
the electrolyte resistance, anodic film capacitance and film resistance respectively. .. 115
Figure 5.8. The relationship between film thickness and anodic voltage before and after
immersion experiments in naturally aerated 3.5% NaCl electrolyte. ........................... 116
Figure 5.9. Potentiodynamic polarization plots of the etched titanium immediate immersed
and immersed for 60 days in naturally aerated 3.5% NaCl electrolyte. ....................... 116
Figure 5.10. Potentiodynamic polarization plots of the anodized titanium in 1 M H SO
2 4
immediate immersion and after immersion for 60 days in naturally aerated 3.5% NaCl
electrolyte. .................................................................................................................... 117
Figure 5.11. Potentiodynamic polarization plots of the anodized titanium in 1 M H PO
3 4
immediate immersion and after immersion for 60 days in naturally aerated 3.5% NaCl
electrolyte. .................................................................................................................... 117
Figure 6.1. Current density-time responses of CP-Ti during anodizing at 100 V (a), 150 V (b)
and 200 V (c) in 1 M phosphoric acid for 900 s at ambient temperature…………….126
Figure 6.2. Scanning electron micrographs of plan-views of the anodic films formed after
anodizing at 100 V (a), 150 V (b) and 200 V (c) in 1 M phosphoric acid. The insets are
higher magnification images of the respective anodic films. ....................................... 127
Figure 6.3. Ultra-high magnification scanning electron micrographs of the anodic films
formed after anodizing at 100 V (a), 150 V (b) and 200 V (c) in 1 M phosphoric acid.
..................................................................................................................................... 128
Figure 6.4. Scanning electron micrographs of cross-sections of the anodic films formed after
anodizing at 100 V (a), 150 V (b) and 200 V (c) in 1 M phosphoric acid. The inset
images are higher magnification images of the respective anodic oxide film. ............ 129
Figure 6.5. GDOES depth profiles of the anodic films formed on CP-Ti at 100 V (a), 150 V
(b) and 200 V (c) in 1 M phosphoric acid; the intensities of phosphorus are multiplied
by 10. ........................................................................................................................... 130
Figure 6.6. Raman spectra of anodic films formed on CP-Ti in 1 M phosphoric acidat 100,

150 and 200 V. ............................................................................................................. 131
Figure 6.7. Electrochemical impedance spectroscopy results of anodic films formed after
anodizing at 100, 150 and 200 V in 1 M phosphoric acid; as plotted in Bode diagrams;
the left direction of arrow corresponds to the impedance modulus/dm.cm2, and right
direction corresponds to the impedance phase/degree. ................................................ 131
Figure 6.8. Equivalent circuit model for anodic porous films formed at 100 V, 150 V and
200 V in 1 M phosphoric acid. ..................................................................................... 132
10