DEVELOPMENT OF TITANIUM - NICKEL

SPUTTERING TARGETS

Performed at Defence Metallurgical Research Laboratory (DMRL)

Hyderabad
A project report submitted in the partial fulfillment of the requirements for the
award of degree
Of
Bachelor of Technology
In
Metallurgy and Materials Technology
By
S. Moulali Reddy (07261A1802)
A. Vigna Sai Sandeep (072621A1803)

Department of Metallurgy and Materials Technology

Mahatma Gandhi Institute of Technology
Hyderabad 500 075
Under the guidance of
Dr. M. Manish Roy, Sc “F”

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 ACKNOWLEDGEMENT

We firstly thank Dr. G. Malakondaiah, Sc ‘H’ &

Director, DMRL, Hyderabad for giving us this opportunity
to carry out our Mini-Project work.

We express our sincere thanks to Dr. Vijaya Singh, Sc

‘G’, Coordinator HRD.

It is a great privilege to record our deep sense of

gratitude to Dr. Manish Roy,
Sc ‘F’, Surface Engineering Group. His stimulating
guidance and constant encouragement has benefited us
to learn the best of Research culture. We are deeply
indebted to him.

We are grateful to Dr. Amit Bhattacharjee, Sc ‘F’,

Titanium Alloy Group for his constant help and support
during our experimental work.

We sincerely thank Mr. A. Anand Rao, Sc ‘G’ and Head,

MEG and Mr. U. Chinta Babu, Sc ‘C’, of MWG, for their
constant help during our experimental work.

We would also like to thank Dr. L. Durai, Sc ‘F’ and Head,

Analytical Chemical Group for his help in the Chemical
Analysis of the specimens.

We wish to thank Prof. P. K. Subramanian, Chair,

Department of Metallurgy and Materials Technology and
Prof. Dr. J. Viplava Kumar, Dean (R&D), MMT, MGIT for
the encouragement they have provided.

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We thank Ms. Vijaya Lakshmi, Mr. Venugopal, of SFA
Group. Our special thanks to Mr. Babu Rao for his
assistance in the Metallography work.

We would also like to thank P. Koteshwara Rao, A.

Sridhar of Titanium Alloy Group and all the staff of
Mechanical Workshop and MEG group for their help in
specimens preparation.

CONTENTS
CERTIFICATE 1
ACKNOWLEDGEMENT 2
LIST OF TABLES 4
LIST OF FIGURES 5
ABSTRACT 6
CHAPTER 1: INTRODUCTION 7
CHAPTER 2: LITERATURE SURVEY 9
2.1 Deposition Technology 10
2.1.1 Uses 12
2.1.2 Applications 13
CHAPTER 3: EXPERIMENTAL DETAILS 15
3.1 Material 15
3.1.1 Charge Preparation 15
3.1.2 Melting 15
3.1.3 Mechanical Processing 16
3.1.4 Electrical Discharge Machining 17

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 3.2 Metallography 18
3.3 X-Ray Diffraction 18
3.4 Chemical Analysis 19
CHAPTER 4: RESULTS 20
CHAPTER 5: CONCLUSIONS 28
CHAPTER 6: REFERENCES 29

LIST OF TABLES

Table 1: Thin Film Application with respect to their properties 14

Table 2: The hardness, melting point and densities of Titanium and

Nickel 16

Table 3: Charge calculations 16

Table 4: Chemical Composition of Ti-25Ni pancake after chemical

analysis 20

Table 5: Chemical Composition of Ti-50Ni pancake after chemical

analysis 20

Table 6: Vickers’s Hardness values of Pancakes 27

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 LIST OF FIGURES

Fig 1: Titanium – Nickel Phase Diagram 9

Fig 2: Classification of thin film deposition techniques 11

Fig 3: Vacuum system used for Thin Film Deposition 12

Fig 4: The Electrical Discharge Cutting Machine 17

Fig 5: Microstructure of Ti-25Ni alloy (100X) 21

Fig 6: Microstructure of Ti-25Ni alloy (200X) 22

Fig 7: XRD pattern of Ti-25Ni alloy 23

Fig. 8: Microstructure of Ti-50Ni alloy (100X) 24

Fig 9: Microstructure of Ti-50Ni alloy (200X) 24

Fig. 10: X-RD pattern of Ti-50Ni alloy 25

Fig. 11: Microstructure of Ti-75Ni alloy 26

Fig. 12: Microstructure of Ti-75Ni alloy 26

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Fig. 13: Sputtering Targets 27

ABSTRACT
Sputtering is one of the most widely used deposition technique. Sputtered NiTi
thin films are commonly deposited in an amorphous state for applications related to
microactuator, microgrippers etc. The main objective of the project is to prepare different
Ti-Ni alloy targets for sputtering. Three different compositions were taken and the
respective targets were prepared using different fabrication processes. Importance was
given priorly to Titanium rich and Nickel rich alloys as Nitinol (Ti-50Ni) characteristics
were already known. The properties like chemical compositon, microstructural features,
hardness and XRD are evaluated. Nickel rich alloy failed due to the formation of brittle
intermetallics (TiNi3) whereas the other two alloys were successfully fabricated into
targets.

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1. INTRODUCTION

Nickel – Titanium Thin Films

NiTi thin films which inherent shape memory effect (SME) and superelasticity
have attracted much attention in the recent years as intelligent functional materials. Thin
film shape memory alloys offer a great potential in the field of micro-electro-mechanical
systems (MEMS) since they can be fabricated by batch processing and patterned with
standard lithographic techniques. The excellent biocompatibility of NiTi has also lead to
the recent research concentrating on the application of thin film SMEs for Bio-MEMS.
Superelasticity, which is widely employed in a variety of bio-medical and consumer bulk
products, from arterial stents to cell phone antennas, may have interesting application in
the form of thin films, e.g. for neurovascular blood vessels in stents applications or as
surface coatings and functionally graded layers for control of degradation due to fatigue,
erosion and wear.

NiTi alloys are inherently very sensitive to composition and, at compositions

close to 50at% of both elements; a 1 at% deviation can cause a shift in the transformation
temperature by around 100°C, resulting in the SME occurring above or below room
temperature. Therefore precise control of composition is essential. The transformation
temperatures are very sensitive to the film thickness when the film thickness is less than
2μm due to residual strain and surface oxidation. In addition, metallurgical factors such
as annealing and aging treatments can affect the transformation temperatures. However,
due to lack of a full understanding of thin film SMAs, together with problems in the
control of deposition parameters, they have received extensive attention in relation to
MEMS technology.
NiTi SMA thin films are often deposited by dc or rf magnetron sputtering,
although the control of film composition and properties can be a challenge. Other recent
studies have suggested that the microstructure and properties of films fabricated using
simultaneous sputter deposition from several targets are very different from those
produced by alloy target.

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 The study of the effect of film composition on phase transformation,
transformation temperatures, microstructure and surface morphology, and mechanical
response is of great importance for the fabrication of devices from such alloys for
MEMS. The phase transformation in SMA thin films is accompanied by significant
changes in the physical, chemical, electrical, and mechanical behavior. Surface
morphology affects the optical, frictional and tribological properties of films, and surface
evaluation can be used to predict shapememory hysteresis. Mechanical properties are
very important from the viewpoint of practical MEMS applications, and nanoindentation
has proven particularly useful in characterizing film properties, largely because there is
no need to remove the films with thickness below1 μm from the substrate.

Thus thin NiTi film is very important for several engineering applications. Such
film can be deposited by several techniques. However, sputtering appears to be most
popular due to several reasons such as ease of operation control of composition etc. The
deposition of NiTi alloy by sputtering requires sputtering target. In view of above,
present investigation is undertaken to fabricate targets for sputtering of Nickel-Titanium
alloy having 3 different compositions.

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2. LITERATURE SURVEY:

Fig 1: Titanium – Nickel Phase Diagram

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2.1 Deposition Technology

Deposition Technology can well be regarded as the major key to creation of devices such
as computers, since the micro-electronic solid state devices are all based on material
structures created by thin film deposition. Electronic engineers have continuously
demanded films of improved quality and sophistication for solid state devices, requiring a
rapid evolution of deposition technology. Equipment manufacturers have made
successful efforts to meet the requirements for improved and more economical deposition
systems and for in situ process monitors and controls for film parameters.

Another important reason for the rapid growth of deposition technology is the
improved physics and chemistry of films, surfaces, interfaces and microstructures made
possible by remarkable advances in analytical instrumentation during the past two
decades. A better fundamental understanding of materials leads to expanding applications
and new designs of devices that incorporate these materials. A good example of crucial
importance of depositon technology is the fabrication of semi-conductor devices, an
industry that is totally dependant on formation of thin solid films of variety of materials
by deposition of gas, vapor, liquid or solid phase. The starting materials epitaxial films of
semi conductors are usually grown by the gas phase.

There are three categories of thin film processes: physical vapor deposition
(PVD), chemical vapor deposition (CVD), and chemical methods. Below figure
illustrates the classification of the different deposition processes. Topics include vacuum
systems, evaporation, sputtering, plating, molecular beam epitaxy (MBE), CVD, laser
ablation and solgels.

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Fig 2: Classification of thin film deposition techniques

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Fig 3: Vacuum system used for Thin Film Deposition

2.1.1 Uses

 Ceramic thin films are in wide use. The relatively high hardness and inertness of
ceramic materials make this type of thin coating of interest for protection of
substrate materials against corrosion, oxidation and wear. In particular, the use of
such coatings on cutting tools can extend the life of these items by several orders
of magnitude.

 Whenever two surfaces make mechanical contact under relative motion, there is
friction and wear. Coatings, made by CVD or PVD are today extensively used on
tools, for metal cutting and forming and on machine elements such as bearings,
gears, seals and valves, to optimize their surface properties. Important

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 phenomena and considerations in real life applications are coating detachment,
permanent surface deformation, cracking, scratching.

 The vapor phase thin film techniques have three significant advantages over the
liquid phase techniques; applicability to any material, wide adjustability in
substrate temperature and access to the surface during deposition.

 Regarding the liquid phase techniques, liquid phase epitaxy (single crystal) is
useful for low cost production but does not have the control of the process.
Electroplating from liquid solution is widely used, occasionally even for epitaxy.

2.1.2 Applications

 Titanium Nitride (TiN) coatings on cutting tool offer hardness, low friction and a
chemical barrier to alloying of the tool with the workpiece.
 They also offer a rich gold color for decorative applications.
 The Cr coating on a plastic part achieves the functionality of the same part made
from bulk metal, but at significant savings in cost and weight.
 The TiN coating achieves surface properties unattainable in a bulk material, since
the bulk material also offer high strength and toughness in the cutting tool
application.

Thus, multilayer thin films can behave as completely new engineered materials
unknown in bulk form. When multiple layering is combined with lithographic patterning
in the plane of the films, microstructures of endless variety can be constructed. This is the
basic technology of the integrated-circuit industry and more recently it is being applied to
optical waveguide circuitry and to micromechanical devices. The latter include such
creations as rotary electrostatic motors tens of micrometers in diameter, which is a clear
case of a device awaiting an application.

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Table 1: Thin Film Application with respect to their properties

Thin Film Property Applications

Reflective/anti reflective coatings

Optical Decoration(color, luster ) Memory discs (CDs)
Interference Filters

Insulation
Electrical & Thermal Conduction Semi-Conductor devices
Barrier layer & Heat Sinks

Magnetic Memory disc

Barriers or Diffusion alloying Gas/Liquid

Chemical
sensors

Tribological (Wear Resistant) Coatings

Mechanical
Hardness, Adhesion

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3. EXPERIMENTAL DETAILS
3.1 Material
The three alloy compositions, namely Ti-25Ni, Ti-50Ni and Ti-75Ni (at %) were
prepared by using Titanium sponge and Nickel plates. The hardness, melting point,
densities of these two metals are summarized in Table 2. Simultaneously the charge
calculations are shown in Table 3. The fabrication of targets for sputtering mainly
involved the following steps:
1. Charge preparation
2. Melting
3. Mechanical processing of the pancake

3.1.1 Charge Preparation

The preparation of the charge firstly involved the conversion of atomic % into
weight %. The formula for the conversion is shown below. A fixed weight (650gm) for
all the compositions was taken .The charge was prepared by using a simple weighing
machine. The charge was then forwarded to the melting to obtain the pancake. The
hardness and melting point of Ni and Ti are given in Table 2. The amount of material
melted for various charges are listed in Table 2

Wt% of A = At. Wt of A X At % of A
Σ (At. Wt of A X At % of A)

3.1.2 Melting
The pancake was prepared by melting in Vacuum Arc Electric Furnace (non
consumable) and casting in the form of pancakes followed by forging. A vacuum arc
electric furnace in which charge can be melted on a water cooled copper crucible under
vacuum 10-3 mbar was employed. Prior to melting, the furnace chamber was purged with
argon gas once and then it was filled with the gas again up to 532 mbar. The charge was
melted by arcing emitted from a tungsten bit brazed to copper stringer rod suspended
above the charge. A DC potential of up to 30-32 volt and current 1000 A was applied

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between tungsten cathode and charge material which formed the anode. A stirring coil
around the copper crucible stirred the melt pool and homogenized the melt composition.
Each pancake was melted four times to homogenise. The pancakes were then forwarded
to the mechanical processing.

Table 2: The hardness, melting point and densities of Titanium and Nickel

Melting Point (° C )
Metal Hardness (V.H.N.) Density ( gm/cc )

Titanium 60 1668 4.54

Nickel 75 1452 8.9

Table 3: Charge calculations

Ti – Ni Amount of Titanium (gm) Amount of Nickel (gm)
25 – 75 138.905 511.095
50 – 50 291.98 358.02
75 – 25 461.435 188.565

3.1.3 Mechanical processing

The pancake obtained was mechanically processed using different processes
such as forging, machining etc. to get a disc of final diameter of 4” and thickness of
4 mm respectively. The mechanical processing of each pancake was different and was
totally dependent on the composition of the pancake.
Forging: The pancake was heated in an electrical furnace upto a 900 oCtemperature and
then for forged using a power hammer. The maximum capacity of the power hammer was

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10000 N. Very low intensity strokes were struck in order to prevent any damage to the
pancake. The hardness of each pancake was measured using a Vickers’s hardness testing
machine. Other than forging, other machining techniques were also used to get the final
disc for sputtering such as lathe machining and electrical discharge machining (E.D.M)

3.1.4 Electrical Discharge Machining

The pancakes were subjected to EDM for better and faster rate of fabrication of the
targets. The general principle of EDM is as discussed below EDM machine is shown in
Fig. 4.

Fig 4: The Electrical Discharge Cutting Machine

To obtain a specific geometry, the EDM tool is guided along the desired path very close
to the work; ideally it should not touch the workpiece, although in reality this may
happen due to the performance of the specific motion control in use. In this way a large
number of current discharges (colloquially also called sparks) happen, each contributing

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to the removal of material from both tool and workpiece, where small craters are formed.
The size of the craters is a function of the technological parameters set for the specific job
at hand.

The debris of the machining processing were taken and used for Metallography, XRD
and chemical analysis.

3.2 Metallography
Small pieces that were obtained after machining were taken and mounted using bakelite
powder in a mounting machine. After mounting the sectioned parts were polished.
Initially rough polishing was done with emery papers 180, 220, 320, 400 and 500; rough
polishing was done to remove the level difference and scratches present onto the
specimen to maximum extent. Later, final polishing was done on 9 µm and 1 µm to give
a mirror finish to the sectioned part. After the final polishing is done the sectioned parts
are cleaned with acetone to remove any minute dust particles.
After polishing, the microstructures were observed under an optical microscope. Later,
the specimens were etched with Kroll’s reagent and the resulting microstructures were
observed again after etching.

3.3 X-Ray Diffraction

X-ray crystallography is a method of determining the arrangement of atoms within
a crystal, in which a beam of X-rays strikes a crystal and diffracts into many specific
directions. From the angles and intensities of these diffracted beams,
a crystallographer can produce a three-dimensional picture of the density
of electrons within the crystal. From this electron density, the mean positions of the
atoms in the crystal can be determined, as well as their chemical bonds, their disorder and
various other information.
For the XRD analysis, a small 10mm X 15mm specimen was prepared using an EDM. X-
ray diffraction (XRD) patterns were obtained from the sample surfaces using Philips PW
1830 diffractometer to examine the structure of sputter target. The X-ray diffractometer
was set at 40 kV and 30 mA with Co K radiation target and a nickel filter. The
diffraction patterns were recorded at a speed of 0.01os-1.

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3.4 Chemical Analysis
Depending on the components to be measured, small pieces of each pancake were cut
using an ‘Isomet’ cutting machine and were forwarded for chemical analysis. The Ti and
Ni content could be directly found by using X-Ray fluorescence gun. Qualitative analysis
was conducted for finding out the amount of Oxygen, Nitrogen, Carbon, Hydrogen and
Sulphur in each of the pancakes.

4. RESULTS
 The composition of the Ti – Ni pancakes after the chemical analysis is as listed in
table 4 and table 5.

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Table 4: Chemical Composition of Ti-25Ni pancake after chemical analysis
Element Titanium Nickel Carbon Sulphur Nitrogen Hydrogen Oxygen

Content 72.71% 26% 0.19% 0.02% 0.06% 0.070% 0.95%

Table 5: Chemical Composition of Ti-50Ni pancake after chemical analysis

Element Titanium Nickel Carbon Sulphur Nitrogen Hydrogen Oxygen

Content 45.87% 54.10%

The optical micrographs of Ti-26 Ni are shown in Fig. 5 and Fig. 6. A dendritic
microstructure is evident. Corresponding XRD pattern is presented in Fig. 7. The
microstructures of Ti-50 Ni are presented in Fig. 8 and Fig. 9. A single phase
microstructure with grain size about 100 m can be seen. Their XRD pattern is given
in Fig. 10. Figure 11 and Fig. 12 represent micrographs of Ti-75 Ni. Presence of
crack is clear in as cast pancake. Microstructure does not reveal any further
information.
 Titanium-25Nickel alloy: Due to the formation of the intermetallics (Ti2Ni), the
pancake failed during forging. Later, a new set was melted and machined by an
EDM to obtain a 2”dia disc.Ti2Ni structure is shown in the microstructures
below.
 Titanium-50Nickel alloy: The pancake was easily machined to get a 4”dia disc
without any difficulty as there were no intermetallic compounds.
 Titanium-75Nickel alloy: Due to the formation of intermetallics (TiNi3), a
cracked pancake was obtained, which couldn’t be subjected to further fabrication
processes. The structure of the intermetallic is shown in the microstructure.
 The microstructures after etching and their respective X-ray diffraction pattern
obtained using a Cu-target of each alloy are shown in the following figures.

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Titanium-25Nickel alloy:

Fig 5: Microstructure of Ti-25Ni alloy (100X)

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Fig 6: Microstructure of Ti-25Ni alloy (200X)

Fig 7: XRD pattern of Ti-25Ni alloy

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 Titanium-50Nickel alloy:

Fig. 8: Microstructure of Ti-50Ni alloy (100X)

Fig 9: Microstructure of Ti-50Ni alloy (200X)

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Fig. 10: X-RD pattern of Ti-50Ni alloy

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Titanium-75Nickel alloy:

Fig. 11: Microstructure of Ti-75Ni alloy

25
Fig. 12: Microstructure of Ti-75Ni alloy

The hardness of the pancakes are tabulated below

Table 6: Vickers’s Hardness values of Pancakes

Composition of the pancake Hardness(Hv)

Ti-25Ni 455

Ti-50Ni 345

Ti-75Ni 370

 The targets for Sputtering prepared are as shown in Fig. 13.

Fig. 13: Sputtering Targets

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5. CONCLUSIONS
 Sputtering is one of the most widely used deposition technique.
 Titanium-25Nickel alloy: The solubility of Ni in α-Ti is very low. At the
eutectoid temperature, it doesn’t exceed 0.2% and is still lower at room
temperature. The maximum solubility of Ni in β-Ti at eutectic temperature is
13%.A eutectic, β (13% of Ni) + Ti2Ni (38 %of Ni), occurs at 28.5% of Ni at
942° C.
 Titanium-75Nickel alloy: A eutectic. TiNi (59% of Ni) + TiNi3 (78.6% of Ni),
occurs at 65% of Ni at 1118° C.The intermetallics make the alloy brittle and
makes it impossible for machining. This composition was a failure.
 Titanium-50Nickel alloy: A single phase region (TiNi) is formed.
Nitinol (Ti-50Ni) has got a rare combination of hardness and shape memory
property. Thus, it is widely used for sputtering and has a wide range of applications in
the construction of actuators, SMA’s, medical applications etc.

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6. REFERENCES
1.Y. Fu, H. Du, W. Huang, S. Zhang, M. Hu, Sens. Actuators, A 112 (2004).
2. J.J. Gill, D.T. Chang, L.A. Momoda, G.P. Carman, Sens. Actuators, A 93 (2001).
3. K.L. Melton, in: T.W. During, K.N. Melton, D. Stockel, C.M. Wayman (Eds.),
Engineering Aspects of Shape Memory Alloys, Butterworth-Heinemann, London,
UK, 1990.
4. S. Sanjabi, S.K. Sadrnezhaad, K.A. Yates, Z.H. Barber, Thin Solid Films 491/1-2
(2005).
5. W.J. Moberly, J.D. Busch, A.D. Johnson, M.H. Berkson, in: M. Chen,
M.O. Thompson, R.B. Schwarz, M. Libera (Eds.), Phase Transformation
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(2001).
11. K. Ken, Gregory Ho, P. Carman, Thin Solid Films 370 (2000).
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shape memory thin films – S.Sanjabi, Z.H.Barber.
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Society. Sensor Division, Electrochemical Society
14. Crystallization of amorphous sputtered TiNi thin films – Ainissa G. Ramirez, Hai
Ni, Hoo- Jeong Lee.
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