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Metal Deposition: Plasma-Based Processes
Chapter · January 2016
DOI: 10.1081/E-EPLT-120053919
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Metal Deposition: Plasma-Based Processes
Neelesh K. Jain
Mayur S. Sawant
Sagar H. Nikam
Suyog Jhavar
Department of Mechanical Engineering, Indian Institute of Technology Indore,
Indore, India
Abstract
Plasma-based metal deposition is one of the most promising emerging areas in surface engineering. It offers a
variety of applications in thin film deposition, thick film deposition, hard facing, repairing, remanufacturing,
surface modification, and complex three-dimensional (3-D) parts manufacturing. Plasma-based metal deposition
processes such as physical vapor deposition and plasma-enhanced chemical vapor depositions have been used
for many years but new processes, such as plasma-transferred arc (PTA) and micro-PTA (m-PTA) deposition
processes capable of 3-D deposition, have attracted the interest of researchers. This entry describes various types
of plasma-based metal deposition processes focusing on their working principle, types, advantages, limitations,
and applications. It also highlights the developments in plasma-based metal deposition processes aimed to
improve deposition rate, deposition quality, and flexibility in selection of deposition and substrate materials.
The entry ends with comparative evaluation of the various plasma-based metal deposition processes described.
INTRODUCTION
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Metal deposition is a very fast growing and demanding
field due to its ability to provide high-end technical solutions for various surface treatment requirements of different
products used in many industries. These requirements
include the need for improving wear resistance, corrosion
resistance, oxidation resistance, chemical inertness, electrical resistance, electrical conductivity, reflectivity, appearance, repairing/remanufacturing, and manufacturing of
complex three-dimensional (3-D) metallic components.
Metal deposition deals with a variety of materials such as
metals, alloys, composites, functionally graded materials
(FGMs), and shape memory materials (SMM) which
require the development of diversified processes using
various energy sources. Advanced materials such as nonferrous alloys (super alloys, titanium-based alloys, etc.),
composites, ceramics, FGM, and SMM possess unique
properties such as high melting temperature, high hardness,
high strength, high toughness, brittleness, etc. making them
attractive to use but difficult to process.
Fig. 1 shows various categories of deposition processes
for metallic materials that are commonly used in industries
to process some of the advanced materials. This includes
processes using laser beam, electron beam, plasma, thermal
spraying, physical vapor deposition (PVD), and chemical
vapor deposition (CVD). Various metal deposition processes have three major applications: 1) thin film deposition; 2) thick film deposition or hard facing; and 3) additive
722
layer manufacturing (ALM). Thin film deposition is used to
modify surface characteristics according to the desired surface properties by depositing a single thin layer (thickness
< 20 µm) or multiple thin layers of a metallic material. Its
various applications include production of coatings for
optical products, electrical appliances, and decorative items
to improve properties such as wear resistance, reduce friction, corrosion resistance, hardness, etc. It can also be used
in microelectronics application for semiconductor deposition, electrical insulator, antireflection coating, etc. The
processes used for thin film deposition are PVD and CVD.
Thick film deposition involves depositing thick layers
(thickness more than 20 µm) of a harder and tougher material on the soft material. Materials such as chromium, titanium, oxides, and carbides of metallic materials are used in
thick film deposition to enhance various surface properties,
such as wear and corrosion resistance, which increase service life of components or can be used to repair worn out
areas. Processes used for thick film deposition include thermal spraying and plasma-based deposition processes. ALM
is the advanced manufacturing application of deposition
processes to generate 3-D products from computer-aided
design (CAD) data by depositing the material layer by layer
to produce near-net-shaped components economically and
with great flexibility. Each deposited layer is created by
rapid solidification of the deposition material over a stationary or moving substrate. The bonding strength between
the substrate and the deposition material depends on deposition energy, deposition pattern, deposition volume, and
Encyclopedia of Plasma Technology DOI: 10.1081/E-EPLT-120053919
Copyright © 2017 by Taylor & Francis. All rights reserved.
Metal Deposition: Plasma-Based Processes
723
heat during deposition which leads to poor metallurgical
properties and inability to produce complex deposition
geometries. Deposition processes, such as PVD and CVD,
involve low-process temperatures and give better performance and better quality for solid material films. However,
they have the major drawback of having a lower deposition
rate compared to other processes.
Among different categories of metal deposition processes, plasma-based processes are fast emerging as energy
efficient, material efficient, and economical processes
which can bridge a gap between capabilities of other deposition processes and can yield good quality metal depositions for a variety of materials. Plasma is defined as the
fourth state of matter produced by energizing the gas atoms
to such a level so that most of them break into free ions. It
can be generated by providing external energy in the form
of electric discharge, radiation, or heat to ionize the gas
molecules. The energy generated by a plasma source can
be used for metal deposition purposes. Plasma-based deposition is carried out by depositing layers of metallic materials over a substrate either to improve its surface properties
or to add delicate 3-D features over an existing component.
Metal Deposition
Laser-Based
Deposition
Electron BeamBased Deposition
Plasma-Based
Deposition
Chemical Vapor
Deposition
Thermal Spraying
Fig. 1 Various categories of metal deposition processes.
interaction time between the deposition and the substrate
material. This enables manufacturing of highly complex
structures with enhanced design freedom, better product customization, optimization, and integration of various functional
features. ALM can be used to manufacture the parts made of
metals, alloys, polymers, ceramics, composites, and FGMs.
Processes based on laser beam and electron beam are
high-energy beam processes; therefore, they are preferred
for focused and low-volume deposition. They suffer from
disadvantages such as high energy consumption, high
investment cost, and high running cost which hinders their
end applications. Thermal spraying provides great flexibility for types of materials to be deposited and provides
higher deposition rate; therefore, this method is preferred
for bulk deposition in large volumes. But these processes
have major limitations such as the use of higher amount of
PLASMA-BASED METAL
DEPOSITION PROCESSES
Various plasma-based metal deposition processes [i.e.,
PVD sputtering, plasma-enhanced CVD, plasma thermal
spraying (PTS), plasma-transferred arc (PTA), and microPTA (m-PTA)] can be classified according to the type of
ionization being used to form plasma, as illustrated in Fig. 2.
In PVD sputtering and plasma-enhanced chemical vapor
deposition (PECVD) processes, the plasma is generated
by ionization caused by electric discharge in the vicinity
of the deposition materials.[1] Some advantages of these
processes include minimization of impurities in the thin
coating, low-substrate heating, and capability to meet functional requirements economically in industrial production.
These processes are used in many applications particularly
in microelectronics and surface engineering. In the processes
Plasma-Based Metal
Deposition Processes
Ionization by
Electric Discharge
PVD Sputtering
Plasma Enhanced
CVD
Ionization by
Thermal Energy
Plasma Thermal Spray
Plasma-Transferred Arc (PTA) Deposition
Micro Plasma-Transferred Arc (µ-PTA) Deposition
Fig. 2 Various types of plasmabased metal deposition processes
on the basis of ionization.
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Physical Vapor
Deposition
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724
such as PTS, PTA deposition, and m-PTA deposition, the
plasma is generated by the ionization caused by thermal
energy. PTS provides higher deposition rate for wide variety
of materials. It is used for the protection of new parts against
wear, high temperature, and corrosion, thus improving the
surface properties. Due to high-heat involvement in deposition, it leads to higher thermal distortion leading to poor
metallurgical properties. PTA and m-PTA deposition processes are used to produce good quality of metal deposition giving good accessibility to the deposition area. These
processes can be used for different applications such as
layered manufacturing of 3-D parts, repairing and adding
features to the existing components.[2] Plasma-based metal
deposition processes provide wider choices in the selection
of deposition and substrate materials, deposition geometry,
deposition characteristics (i.e., composition, pattern, density,
etc.), preprocessing conditions, and post-deposition properties. Various plasma-based metal deposition processes are
described in the subsequent subsections.
PVD-Sputtering Process
Metal Deposition: Plasma-Based Processes
and energy of the ions. Direction of striking by ions can be
controlled by electric and magnetic fields. The ejected deposition material molecules move toward the substrate with or
without collisions with other ejected molecules and inert
gas ions depositing thin coatings on the substrate. Further
nucleation and film growth occur at the substrate due to
condensation of the target atoms changing composition,
microstructure, residual stress, and physical properties of the
deposited layers. This coated film can be influenced by bombardment of low-energy particles, ions, and energetic particles back-scattered from the target and the inert gas.[4] This
enables the process to control the properties of deposition.[5]
This process does not require thermal energy, hence it is also
called nonthermal vaporization deposition. Consequently,
this process offers advantage of low-temperature deposition
for a variety of coating materials such as metals, ceramic,
alloys, metal oxides, etc. Technological advances have
allowed this process to be widely used in industries. Generally, DC sputtering is used for metals, while radio frequency
(RF) potential is used for nonconducting materials. In some
applications, separate ion beam source is convenient for the
deposition of self-contained discharge with ion acceleration.
Working principle
Sputtering rate
Fig. 3 depicts the working principle of the PVD-sputtering
process in which a substrate is made as anode and the deposition or target material is made as cathodes, which are separated by a distance in the range of 5–10 cm in a chamber
having vacuum in the range of 10−6 to 10−10 torr. Flow of an
inert gas such as argon (Ar) is continuously provided to the
vacuum chamber in which its molecules become positively
charged ions ejecting electrons under applied high pressure
and voltage. The ejected electrons may further ionize other
gas atoms to sustain the glow discharge and create a cascading process until all the gas molecules ionize.[3] These ions
strike the cathodic deposition material-ejecting molecules
from its surface by transfer of their momentum. This phenomenon is known as sputtering. The interaction between
inert gas ions and the target material depends on the velocity
Sputtering yield is defined as the number of target atoms
ejected per incident ion. It depends on the target material,
binding energy of target material, relative mass of gas ions
and target atoms, current density, and angle of incidence of
bombarding ions. It is an important quantity in calculating
sputtering rate of a target material which is given by Eq. 1:
R ¼ 62:3 JSMA
ðA per minuteÞ
r
ð1Þ
where J is the ion current density (mA/cm2), S is the sputtering yield (atoms/ion), MA is the atomic weight of the target
material (grams), and ρ is the density of the target material
(gm/cm3). The sputtering rate can be increased by increasing
the discharge current for a given applied voltage.[6]
Applications
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PVD sputtering is advantageous for processing the materials having very high melting temperature. The major areas
of application for PVD sputtering are thin film deposition
for thermal insulation, thin antireflection coatings, decorative coatings, carbide coatings, and corrosion protective
coatings used in various applications such as microelectronics devices, optical applications, metal cutting tool,
magnetic, and optoelectronics.[7]
Variants of PVD-sputtering process
Fig. 3 Working principle of PVD-sputtering process.
Wide ranging industrial applications of PVD-sputtering process motivated researchers to improve the basic version of
Metal Deposition: Plasma-Based Processes
725
PVD-Sputtering Processes
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Balanced
Magnetron
Sputtering
Deposition
Unbalanced
MagnetronSputtering
Deposition
TriodeSputtering
Deposition
Closed FieldUnbalanced
MagnetronSputtering
Deposition
MagnetronSputtering
Deposition
Reactive
MagnetronSputtering
Deposition
PVD-sputtering process to enhance sputtering rate, deposition quality, and process control. This has led to the development of different variants of PVD-sputtering process, as
shown in Fig. 4, which are described in following paragraphs.
Planar diode glow discharge-sputtering deposition
It is the basic version of PVD-sputtering process. It finds
many applications due to its ease of fabrication and applicability for wide range of materials. But it suffers from
disadvantages such as substrate heating, low deposition
rate, low ionization efficiency, and relatively small deposition surface areas.[8]
Triode-sputtering deposition
Triode-sputtering deposition process involves use of an
additional heated filament to increase the electron density
in plasma by thermionic emission, as depicted in Fig. 5.
Ion BeamSputtering
Deposition
Pulsed
MagnetronSputtering
Deposition
Biased Target Ion
Beam Deposition
High-Power
Impulse
MagnetronSputtering
Deposition
Fig. 4 Different variants of
PVD-sputtering process.
Use of triode increases ionization efficiency of plasma to
generate intense sputtering discharges which enables higher
discharge rates even at lower target voltages and lower
pressures as compared to conventional PVD-sputtering
process using DC Sometimes, filament reacts with the
working gas and produces scaling that tends to erode filament rapidly during deposition thus lowering the sputter
rate. Although, this process is used for thick coating, but
maintaining uniformity of coating is difficult due to lack of
electron path guiding mechanism to confine the plasma.[9]
Magnetron-sputtering deposition
The working principle of magnetron-sputtering deposition
process is shown in Fig. 6. In this process, permanent
magnets are arranged below the target plate so as to produce magnetic field near the target material. It concentrates
the electrons and causes them to travel spirally along the
magnetic flux lines near the target instead wandering
Fig. 5 Working principle of
triode-sputtering
deposition
process.
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Planar Diode Glow
Discharge-Sputtering
Deposition
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726
Metal Deposition: Plasma-Based Processes
Fig. 6 Working principle of
magnetron-sputtering deposition
process.
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around the target material. This is referred as balanced
magnetron-sputtering deposition. It increases ionization
efficiency due to more collisions with gas molecules.
Therefore, this process can be operated at lower pressure
with higher current densities and provides higher sputtering
rate and generates stable plasma.[10,11] In some cases,
higher current densities near the target may be undesirable
because they reduce ion bombardment over the substrate
which reduces the chances of desired modification of the
growing film. An altered magnetic configuration can be
obtained by extending the plasma region toward the substrate from vicinity of the target. This can be achieved by
increasing magnetic strength of the outer magnets as compared to the middle magnet. It increases electron and ion
current densities near the substrate that increases ions bombardment on the growing film.[11,12] This is known as
unbalanced magnetron-sputtering deposition. This process
is advantageous to produce high deposition rate, welladhered, and highly dense coatings. It has several diverse
applications such as coatings of noble metals such as gold
(Ag) and silver (Au) for making electrical contact,[13] niobium coatings for biological applications,[14] and electrical
applications of niobium nitride coatings.[15]
Despite several advantages offered by unbalanced
magnetron-sputtering deposition process, it is difficult to
uniformly produce coatings for complex components at a
good deposition rate. Therefore, multiple magnetron systems
have been introduced to develop a process known as closed
field unbalanced magnetron-sputtering (CFUMS) deposition. Fig. 7 compares magnetic configuration and plasma
confinement in balanced, unbalanced, and closed-field
magnetron-sputtering deposition processes. In the CFUMS
deposition process, multiple magnets are used to form a
closed trap of electrons through multiple magnetic field lines
in the plasma. Hence, electron energy losses to the chamber
walls are minimized and dense plasma sustained near the
substrate region lead to high ion current densities.[16] It is
well suited to deposit different materials such as pure metal,
nitrides, and amorphous hydrogenated carbon coatings,[17]
CrAlTiN coatings for reducing the coefficient of friction,[18]
and coating with graded properties.
Reactive magnetron-sputtering deposition is another
important variant of the PVD-sputtering process which is
commonly used to deposit compound thin coatings. Here,
reactive gases [i.e., nitrogen (N2) and oxygen (O2)] are
intentionally added which react with the sputtered material
to form a wide variety of useful compounds. The reaction
can be controlled by adding the desired percentage or
enough gas to ensure complete reaction of sputtered material. This process is limited to low deposition rate and
sometimes produces arc-induced coating defects, i.e., arcing.[19] The arcing effect at the target leads to the ejection of
droplet materials from the target which results in defects on
the growing coating. The reactive gas is expected to form
compound coating on substrate and cathode surface. The
formation of compounds over cathode surface reduces the
deposition rate which is called as poisoning effect.[20] The
bipolar-pulsed technique is used in reactive magnetronsputtering process which reduces the chances of arcing and
produces high deposition rate. This process has been used
for the deposition of different materials such as copper
(Cu)–chromium (Cr)–O thin coatings,[21] Cu(In, Ga)Se2
absorber layers on CuGa substrate,[22] and niobia
(Nb2O5)/silica (SiO2)-mixed oxide thin films.[23]
Pulsed magnetron-sputtering deposition utilizes RF in the
range of 5–30 MHz. This RF is developed because of the
727
Fig. 7 Comparison of the magnetic configuration and plasma
confinement in balanced, unbalanced, and closed-field magnetron-sputtering
deposition
processes.
Source: From Arnell & Kelly.[11]
©1999 Elsevier. Reprinted with
permission.
difference in mobility between electrons and ions. This
mobility difference leads to the development of negative
potential on the target. This process is particularly useful for
the deposition of an insulating coating or dielectric materials.
It alleviates problems of poisoning and arcing associated
with reactive magnetron-sputtering deposition. In this process, the charging takes place during pulse-on time only and
discharging takes place during pulse-off time. This significantly reduces the arcing problem while depositing insulating materials.[11] It also reduces defects in growing coating
and approaches higher deposition rate.[24] Use of this process
has led to significant improvement in coating properties
which can be used in different applications such as low
friction titanium nitride (TiN) coating, aluminum-doped zinc
oxide transparent conductive coating, and copper indium
diselenide on photovoltaic devices.[25]
High-power impulse magnetron-sputtering deposition is
a relatively new process in which high discharge pulse power
is supplied for a short period time. This results in high
plasma density and highly ionized flux of the sputtered material which allows better control of the dense coating growth
by controlling the energy and direction of the deposition ions
and electron.[26] Pulsation of power favors diffusion and
renucleation during thin film growth and avoids overheating
of target.[27] The major disadvantage of this process is the
typically lower deposition rate due to back-attraction of ionized sputter materials, i.e., not available for film growth. It
has different applications in coatings, for example, thin films
for automotive applications,[28] TiAlCN/VCN coatings for
tribological applications,[29] and aluminum nitride for
improving the mechanical properties.[30]
target material for its sputtering and deposit it on a suitably
placed substrate to form a thin coating on it, as shown in
Fig. 8. Ion source such as Kaufman or duoplasmatron is used
for thin film deposition by extracting a maximum amount of
target material.[6] In this process, the substrate temperature,
gas pressure, and ion bombardment can be independently
controlled due to a separate ion source. It also reduces substrate heating. An additional secondary ion source may be
used for enhancement in properties of the sputtered film
growth.[31] In the IBSD process, a fraction of ions may not
hit the target material but may hit the surroundings causing
contamination of the coated film. Consequently, a new
biased target ion beam deposition process has been developed to overcome problems of the IBSD process. In this
process, a highly negative bias is applied to the target material while surroundings are grounded, so that most of ions
will accelerate toward the negatively biased target material
thus reducing contamination of the coating. This process
Ion beam sputter deposition
Ion beam sputter deposition (IBSD) is a vacuum-based
deposition process that uses a separate ion source to generate a focused high-energy ion beam directed toward the
Fig. 8 Working principle of ion beam-sputtering deposition
process.
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Metal Deposition: Plasma-Based Processes
728
uses low energy ion sources by combining end-Hall ion
and hollow cathode electron sources together for sputtering. The hollow cathode electron source is used for ejection of electrons whereas end-Hall ion source is used to
maintain stable plasma. This kind of ion source produces a
very high density of inert gas ions that increases deposition rate as compared to conventional IBSD.[32,33] This
method enables to deposit different nonmagnetic materials
such as chromium, titanium, Ag, magnetic materials such
as iron, cobalt, nickel, etc., and dielectric materials such as
aluminum oxide, silicon oxide, etc.
Plasma-Enhanced CVD
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Working principle
Fig. 9 depicts working principle of plasma-enhanced CVD
process in which a mixture of an inert gas and reactant gases
is supplied between the ground substrate and the cathode.
Here, the inert gas ionizes to form capacitive coupling
between substrate and cathode by supplying 13.56 MHz
RF power to the cathode. Ionization of the inert gas molecule
helps in dissociation of reactant gas which further reacts with
other gas molecules or substrate material to form a new
compound at the surface of the substrate.[34] The process
involves chemical action, hence no subsequent heat is generated during the process. A variety of thin films can be
deposited on the temperature-sensitive substrates. The temperature generated during process generally is in the range
from 250°C to 350°C which is quite low as compared to the
conventional CVD process. Another main advantage of
PECVD is the formation of ions through inert gas which
Metal Deposition: Plasma-Based Processes
may bombard on the growing thin film coating. This plays
an important role in growth kinetics, nucleation, stress, structure, and properties of the deposited material.[35] Highdensity power sources such as microwave (MW-PECVD)
and electron cyclotron resonance (ECR-PECVD) can also
be used for deposition of advanced materials.[36]
Advantages and disadvantages
PECVD offers many advantages such as low working temperature, uniform deposition, good deposition on corners
and steps, less porosity, good adhesion with substrate, and
more flexibility in working with different depositing materials. Better control of PECVD process parameters allows
tailoring of mechanical, chemical, electrical, and optical
properties, stoichiometry, and residual stresses of the deposition. It has some disadvantages such as generation of
toxic by-products, problems in depositing pure metals, and
costly process equipment.[6]
Applications
Materials typically deposited using PECVD include silicon
carbide, silicon nitride, silicon dioxide, and amorphous silicon. Silicon nitride and silicon dioxide are the commonly
used insulating materials in the fabrication of electronic
devices. PECVD finds various thin film deposition applications in different fields such as microelectro-mechanical
systems (MEMS) to improve optical and mechanical properties,[37] depositing superconducting materials such as niobium–germanium (Nb3Ge) and (CuMo6S8), semiconductor
deposition, depositing diamond-like carbon film (DLC) as
antireflection coating,[38] and microcrystalline silicon thin
film for solar cells.[39]
Plasma Thermal Spraying
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Increase in demand for coating of high temperature, corrosion, and wear-resistant materials led to the development of
PTS which is a specific term for a group of coating processes
used to apply metal or nonmetal coatings.[40] The first industrial plasma spray torch appeared in the 1960s. Earlier versions of PTS processes used deposition material in the form of
wire which can be melted by combustion flames generated by
O2/acetylene gases in a process known as high-velocity oxyfuel coating. But the use of deposition material in the powdered form necessitates plasma to generate high temperature
for powder melting and deposition and accordingly modifications in the torch design. Consequently, this process is
referred as PTS which is very efficient for medium-to-high
velocity deposition and yields higher bonding strength.[41]
Working principle
Fig. 9 Working principle of PECVD process.
Fig. 10 shows the concept of the PTS process using deposition material in the powdered form. Plasma is generated
Metal Deposition: Plasma-Based Processes
729
Plasma Thermal
Spraying
Atmospheric
Plasma
Thermal
Spraying
Vacuum
Plasma
Thermal
Sprayin
Inert Gas
Plasma
Thermal
Spraying
Shrouded
Plasma
Thermal
Spraying
Under water
Plasma
Thermal
Spraying
Fig. 12 Variants of plasma thermal spraying process.
Concept of plasma thermal spraying process.
by feeding an inert gas such as Ar or helium (He) through
the gap between the cylindrical tungsten (W) cathode and
anodic Cu nozzle.[42] When the gas passes through the
nozzle, the electrons coming out from the cathode ionizes
the gas molecules, thus generating plasma which is accelerated toward the nozzle exit. Energy and temperature distribution of the plasma arc depends on physical properties
and type of plasma gas. Deposition material in the powder
form is supplied through a carrier gas. It can be supplied
either externally or injected internally through a powder
port into the high-energy plasma. Location and angle of
powder port depend on the nozzle design of the plasma
torch.[43] Different process parameters of PTS are shown
in Fig. 11. Deposition characteristics are determined by the
behavior of powder particles in the plasma arc (i.e., melting
temperature and particle moving trajectories) which in turn
is governed by condition of plasma arc (i.e., type and flow
rate of plasma gas and plasma temperature), powder particle parameters (i.e., type, size, shape, and velocity), and
process parameters (i.e., power supply, stand-off distance,
and plasma torch velocity). Powder particle velocity
depends on the feed rate of the powdered material, type
of plasma gas, and other process parameters.[44] It is one
of the important factors in PTS because the powder particles sprayed through various trajectories of plasma arc play
Conditions of plasma arc
• Type of plasma gas
• Plasma gas flow rate
• Plasma temperature
Plasma
thermal
spraying
Types
Plasma thermal spraying process can take place under different working conditions and pressure levels. Based on
these, it has five variant as listed in Fig. 12 and these are
described in following paragraphs. In all these variants, the
concept of plasma thermal spraying remains the same.
Selection of a particular process variant can be carried out
on the basis of type of coating material.
Atmospheric plasma thermal spraying (APTS). This
process variant is performed under atmospheric conditions
which causes the surrounding air to enter into the plasma
arc and interact with the molten powder particles leading to
its oxidation. Therefore, it is widely used for depositing the
ceramics and those metals and alloys which are insensitive
toward oxidation. Many applications require coating of
wear and corrosion resistance material, hence atmospheric
plasma spraying process can be used for such application.[47] This process has been used for coating the
mechanically alloyed nanocomposites having matrix of
6061 aluminum alloy reinforced with silicon carbide,[48]
producing coating of hydroxyapatite (HA) material,[49]
Process parameters
• Power supply
• Stand-off distance
• Plasma torch velocity
Behavior of powder particles in plasma arc
• Melting temperature
• Particle moving trajectories
Powder particle parameters
• Type, size, and shape of powder particles
• Velocity of powder particles
Deposition characteristics
• Deposition geometry
• Bonding strength
• Deposition efficiency
Fig. 11 Process parameters of
plasma thermal spraying.
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Fig. 10
a vital role in melting the powder particles.[45] Deposition
profile depends on the volume of material deposited per
unit time and velocity of the plasma torch. Deposition
thickness depends on mass flow rate of the powder, velocity of the plasma torch, and number of passes. This process
can deposit high melting point materials easily due to use of
high temperature generated by the plasma jet.[46]
730
nano-structured zirconia,[50] and mixture of aluminum
oxide and titanium oxide.[51]
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Vacuum plasma thermal spraying (VPTS). In this variant, the coating is done in a closed vacuum chamber under a
vacuum maintained in the range of 10–50 kPa. Particular
value of the vacuum is selected accordingly to the quality of
coating required. This avoids oxidation of the coating and
heat losses which result in high-quality dense coating without porosity.[49] It has been used for tungsten carbide and
cobalt coating for wear and friction resistance,[52] for nanostructured titanium oxide coating,[53] and to fabricate dense
molybdenum disilicide (MoSi2) and its composite reinforced with SiC and TiB2,[54] and NiTiZrSiSn coating
powder for amorphous formation.[55]
Inert gas plasma thermal spraying (IGPTS). Deposition
is performed in a closed chamber filled with an inert gas in
the IGPTS process. The VPTS process does not provide
complete protection from oxidation and sometimes presence of air due to low vacuum may cause oxidation of
substrate and coating material.[40] This process is used for
coating of zirconium bromide material to improve the electrical conductivity of stainless steel substrate[56] and for
biomedical applications of HA and fluorapatite thin film
coatings.[57]
Shrouded plasma thermal spraying (SPTS). Shrouded
plasma spraying is a chamber-free process to reduce the
problem of oxidation by covering the plasma arc with an
inert gas atmosphere, i.e., the area between the torch and
the substrate is flooded with high volume of inert gases. O2
content present in plasma arc is reduced and extra addition
of O2 to plasma arc is avoided by shrouding the plasma arc
thus protecting the coating material against oxidation.[42]
This process has been used for coating of MCrAl (where M
is nickel, cobalt, and/or iron) alloys,[58] coating tungsten
(W) and Cu for nuclear fusion applications,[59] nickel chromium (Ni–20Cr), and stellite-6 powders on boiler tube
steels,[60] 316 L stainless steel coating.[61]
Metal Deposition: Plasma-Based Processes
2) less thermal distortion of substrate due to absence of
direct contact between the flame and substrate; and 3)
production of cleaner and denser coating with high bonding
strength.[64] Whereas its main disadvantages include
1) applicable for hard materials only; 2) difficulty in controlling the parameters of plasma arc spray; 3) loss of
powder particles during passage of plasma; and 4) more
expensive and complex process.[65]
Applications
Plasma spraying has wide variety of applications in aerospace, automotive, and structural industries particularly for
coating the substrate with the wear and corrosion resistance
materials.[48] Atmospheric plasma spraying is used for
coating movable parts like printing rollers, steel rollers, etc.
with oxide materials to increase their corrosion and abrasion resistance.[66] Some applications such as turbine
blades get corroded due to atmospheric contamination,
hence they should be coated with the corrosion resistance
materials such as nickel and chromium but the coating
process should be oxidation-free, hence vacuum, inert gas,
or shrouded plasma thermal spraying process can be
used.[67] Some applications such as ship-building industries
and petroleum industries require underwater coating of the
substrate to protect it from corrosion; in such cases, underwater plasma spraying process can be used.[62]
PTA Deposition
Concept
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Underwater plasma thermal spraying (UPTS). In this
variant, coating is performed under water. A stream of an
inert gas is supplied which pushes the water away from
plasma arc zone and then the plasma is generated. The inert
gas environment around the plasma protects: 1) the plasma
from contacting the water; 2) the sprayed deposition particles from oxidation; and 3) the substrate and the coating
from the corrosion.[62] This process mainly used for coating
of chromium nickel compound (Cr23Ni14) and stainless
steel 304 on the components of boiling water reactors.[63]
PTA deposition process is an advanced form of gas W arc
deposition process in which a pilot arc is produced between
the negatively charged W electrode and positively charged
and water-cooled Cu-constricting nozzle, as shown in
Fig. 13. This pilot arc ionizes the inert gas and creates an
arc between the nozzle and the substrate resulting in the
generation of high power plasma which can produce an
instantaneous temperature of the order of 25,000°C. This
plasma is forced through a constricted nozzle, which
expands and accelerates toward the substrate. The plasma
jet prevents the entry of surrounding gases into the deposition zone and provides a better shield to avoid contamination.[68] Deposition material can be used either in powder
or wire form depending upon the application. Energy and
temperature of PTA deposition depend on the power used
to generate plasma which is determined by type of power
supply (i.e., continuous or pulsed), current (20–400 A),
plasma gas flow rate (0.1–10.0 L/min), pulse frequency,
duty cycle, and the orifice diameter.
Advantages and disadvantages
Advantages and limitations
Major advantages offered by PTS process are: 1) flexibility
in choosing high melting temperature coating material;
The PTA deposition process has many advantages over
arc-based process such as higher deposition rates, lesser
731
Fig. 13 Working principle of
PTA deposition process.
heat-affected zone (HAZ), higher heat efficiency, better
quality of deposition, safer operation, potential to control the
size, flux, velocity, trajectory, and thermal states of both the
deposited and substrate materials. PTA deposition process
yields high-strength metallurgical bond between the alloys
coating and the underlying substrate. But it has some limitations such as higher cost than arc-based processes though it
is cheaper than the high-energy beam (i.e., laser or electron
beam)-based deposition processes, inability to produce
sharper and smaller deposition which can be easily produced
by high-energy beam-based deposition processes.[69]
Applications
PTA deposition process is well suited for coating and bulk
deposition of superior mechanical properties possessing
metallic materials, alloys, and composites. Some specific
applications include steel coating of engine block bores,[70]
thick coating of composite of ferrous nickel alloy (γ/Fe, Ni)
reinforced with titanium carbide on plain carbon steel to
increase in wear resistance,[71] and depositing Ti–6Al–4 V
titanium alloy for ALM.[72]
MICROPLASMA-BASED
DEPOSITION PROCESSES
Need and Concept of µ-PTA
Deposition Process
Arc-based deposition processes are conventional low-cost
metal deposition processes, using high amount of heat and
giving higher deposition rate, greater HAZ, higher dilution,
and higher distortion. While high-energy beam-based processes are capital-intensive processes which can be primarily used for focused and precise deposition with low
HAZ, dilution, and distortion. With the advancement in
digital power supply and process control, it has become
possible to develop microversion of PTA deposition process (referred as µ-PTA deposition process) which can be
operated at very low current of the order of 100 mA that
too with finer control and higher precision. The process
has potential to bridge the gap between process capabilities of arc-based and high-energy beam-based deposition
processes.
The principle of plasma generation in the μ-PTA
deposition process is essentially same as that in the PTA
deposition process. Basis difference is the amount and
control of the current used, which can be as low as
0.1 mA. This enables the µ-PTA process to generate
precisely controlled and focused microplasma arc which
gives almost negligible HAZ, low material distortion,
deeper penetration, depositions free from porosity and
inclusion, and a better appearance without any spatter
marks. Additionally, it offers advantages such as
improved steady arc direction, increased arc stability,
and greatly reduced sensitivity to changes in arc length
and has potential to be energy efficient, material efficient, economical, and environment friendly. The equipment can be automated with the use of a computer
numerical controlled (CNC) machine or robotic arm and
can be operated either in continuous or pulsed power
mode. The μ-PTA deposition process suits best for miniature or small amount of metal depositions which is
required in the repair/remanufacture of defective/damaged dies, gears, and similar engineering components.
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Metal Deposition: Plasma-Based Processes
732
Metal Deposition: Plasma-Based Processes
Process variants
Variants of µ-PTA deposition process can be developed
depending upon the state of the deposition material used.
Deposition material can be used either in the form of wire,
powder, or combination of both. This affects the process
parameters and produces variation in the material deposition characteristics in terms of quality, strength, and size.
Preference could be made for individual characteristics and
their advantages and limitations. All these details are discussed in the following paragraphs.
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µ-PTA Wire Deposition Process
In this variant, deposition material is used in the form of
microsized wire. It utilizes an automatic plasma source
which offers many advantages such as reduced costs and
reduced lead times, fabrication of complex components,
repair or remanufacture of high-value components, rapid
prototyping, and low volume production. This process can
also be used for ALM applications to build complex structures having multilayer and/or multimaterial and/or multitrack (i.e., depositing materials side by side) depositions.
Use of wire as deposition material is advantageous to
enhance quality of deposition, material and energy utilization, environment friendliness, and simplicity of the process equipment and to reduce contamination during the
storage and health hazards. Small sized wires are preferred
for miniaturization and small amount of metal deposition.
Fig. 14 Deposition by m-PTA wire deposition process.
optimum values and keep them constant throughout the
deposition process. These parameters can be selected by
conducting various pilot experiments.
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Working principle
Modeling of deposition geometry
Fig. 14 depicts the process of deposition by µ-PTA wire
deposition process in which tracks over a substrate surface
are deposited using a computer-controlled microplasma and
continuous feeding micro-sized metallic wire as deposition
material. The microplasma torch generates sufficient
amount of heat to melt the wire allowing the formation of
a strong metallurgical bond between the deposition material
and the substrate. Relative motion and manipulation
between the plasma torch and the substrate are required
to generate the required deposition geometry. A robotic arm
or CNC platform can be used to control the relative motion
during deposition. The three parameters namely plasma
power, travel speed, and wire feed rate influence the deposition geometry. Combination of plasma power and travel
speed controls the heat available to the melt pool, which
directly governs the width of deposition, while the combination of wire feed rate and travel speed governs the availability of deposition material to the melt pool, which affects
the height of the deposition.[73] Various combinations of
wire feeding arrangements such as front feed, back feed,
and side feed are possible during this process, as shown in
the Fig. 15. Type of feeding arrangement affects the metal
transfer mode between the wire and the melt pool. Before
deposition, it is important to set all these parameters to their
In any deposition process, the geometry of deposition is
mainly governed by the combination of various process
parameters, i.e., power supplied, travel speed of worktable,
and wire/powder feed rate.[74] A number of models predicting the deposition geometry profile have been developed
for various ALM processes to understand the relationship
Fig. 15 Front feed, back feed, and side feed arrangements.
Metal Deposition: Plasma-Based Processes
733
between the different process parameters and the profile
obtained in its cross-section. Fig. 16 depicts the schematic
arrangement of the cross-section of typical single-track
geometry used for modeling. The deposition geometry is
described in terms of track width “w” and track height “h.”
The cross-sectional area depends upon the geometric function f(x) used to describe the shape of the deposition profile.
Table 1 presents the summary of various models developed using various geometric functions for predicting the
single-track geometry. It is seen that the parabolic and
cosine function arc geometries are more identical for the
deposition profile having lower aspect ratio of the deposition (i.e., ratio of track width to track height). While circular
arc-based geometry is preferred for higher aspect ratio
deposition tracks.[71] A model considering deposition as
an arc of ellipse was found to be closer for deposition
geometry generated by µ-PTA wire deposition process.
Comparative study was made in order to check the
accuracy of predicted geometry considering arc of parabola, circle, cosine, and elliptical function. The model was
further used to predict the distance between the two successive tracks “St” in order to minimize surface waviness,
as shown in Fig. 17. The predicted distance between the
two successive tracks St was used to produce multiple-track
deposition. It can be seen from micrograph of Fig. 18 that
surface formed by the overlapping deposition is smooth,
sound, with minimum waviness, free from deposition
defects, and characterizing high efficiency of the µ-PTA
wire deposition process. Various modeling approaches are
helpful in order to control the geometric parameters.
Characterization of deposition geometry
The typical geometry of a single-track deposition is
defined in terms of the track height “h,” track width “w,”
deposited area “A1,” and diluted area “A2,” as shown in
Fig. 19. Aspect ratio and dilution are the two most
Table 1 Summary of various models developed for the geometry of the deposition track.
Geometry of
deposition
track
Arc of a
parabola
Mathematical relations
For the symmetric parabola curve passing
through points B (w/2, 0) and C (0, h)
y ¼ w4h2 x2 þ h
Arc of a
circle
Arc of a
cosine
function
Arc of an
ellipse
Area
Ap ¼
w=2
Ð
w=2
w4h2 x2 þ h dxAp ¼ 23 wh
i
w=2
Ð hpffiffiffiffiffiffiffiffiffiffiffiffiffiffi
Aa ¼
r2 x2 þ ðh rÞ dx
For an arc of a circle passing through points
w=2
B (w/2, 0) and C (0, h) and having radius “r:”
pffiffiffiffiffiffiffiffiffiffiffiffiffiffi
Solving
it gives:
w wpffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
y ¼ r2 x2 þ ðh rÞ where “r” is given by:
2
r2 0:25w2
A
¼
r
arcsin
þ w ðh r Þ
2
a
2
2r þ
h þ0:25w2
r ¼ h cos
2h
w=2
Ð
For a cosine function curve passes through
hcos px
Ac ¼
w dx
w=2
point B (w/2, 0) and C (0, h)
Solving it gives:
y ¼ h cos px
w
Ac ¼ p2 wh
w=2
Ð qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2
For a elliptical function curve passes through Ae ¼
1 wx 2 h2 dx
w=2
point B (w/2,
and C (0, h)
q0)
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2
Solving it gives:
x2
y ¼ f ðxÞ ¼
1 w2 h
Ae ¼ p4 wh
Note: GMAW, Gas Metal Arc Welding.
ALM
process
Researchers
GMAW
Xiong
et al.;[75]
Suryakumar
et al.[76]
Laser metal
deposition
shaping
Zhang
et al.[77]
GMAW
Xiong et al.[75]
Metal
active gas
Cao et al.[78]
GMAW
Xiong
et al.[75]
µ-PTA
wire
deposition
Jhavar
et al.[74]
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Fig. 16 Schematic arrangement of the cross-section of typical
single track geometry.
Source: From Jhavar, Jain, et al.[74] ©2014 Taylor & Francis.
Reprinted with permission.
Fig. 17 Schematic representation of the cross-section of overlapped track deposition.
Source: From Jhavar, Jain, et al.[74] ©2014 Taylor & Francis.
Reprinted with permission.
734
Metal Deposition: Plasma-Based Processes
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Fig. 18 Optical micrograph of the successive tracks deposition
based on predicted model.
Source: From Jhavar, Jain, et al.[74] ©2014 Taylor & Francis.
Reprinted with permission.
important parameters in the single-track deposition. A favorable range of aspect ratios is essential to avoid inter-run
porosity during the multitrack deposition. Dilution is the
ratio of deposited area A1 to the sum of diluted area A2 and
the deposited area A1 and is expressed in percentage. Dilution quantifies the relative amount of substrate material
mixed with the deposited material. Jhavar et al.[73] have
demonstrated that a minimum threshold of dilution is important for good metallurgical bonding between the substrate
and the deposited material. But higher value of the diluted
area A2 would result in higher thermal damage to the deposition, more residual stresses, and higher distortion. It was
also found that smooth and regular depositions can be
achieved for the aspect ratio ranging from 1.3 to 4.0 and
percentage dilution ranging from 2% to 8% during deposition of AISI P20 tool steel by µ-PTA wire deposition process.
Deposition of two or more successive overlapping tracks
over a surface is required to create a new surface or to repair
an existing surface. This can be achieved by multitrack
deposition, as schematically shown in Fig. 20A. The quality
of multitrack deposition can be defined by the deposition of
defect-free surface, surface finish, and the surface waviness
achieved. Once the optimum parameters of single-track
deposition are identified for a given deposition, i.e., height,
width, and area of cross-section then the overlapping distance St can be modeled which governs overlapping and
Fig. 20 Multitrack deposition obtained by Ocelík et al. using
(A) St < 50% of w; (B) St = 50% of w; and (C) St > 50% of w.
Source: From Ocelík, Nenadl, et al.[79] ©2014 Elsevier. Reprinted
with permission.
valley area, as shown in Fig. 20B. Higher surface finish and
surface waviness can be achieved through optimizing the
value of St. Higher St can result in inter-run porosity and
wavy surface. Effect of these parameters is explained by
Ocelík et al.,[79] as shown in Fig. 20C.
Multilayer deposition is required to deposit a new
surface or to repair an existing surface of thickness more
than the height of single deposition track h. Fig. 21 shows
cross-section of a typical multilayer deposition. A typical
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Fig. 19 Cross-section of a typical single-track deposition.
Fig. 21 A typical multilayer deposition.
Metal Deposition: Plasma-Based Processes
735
multilayer deposition has irregular side surfaces due to
inter-layer waviness and requires subsequent finishing.
To evaluate these parameters, the multilayer deposition
is cut in the transverse direction to the deposition. The
sample has to be prepared using standard metallographic
procedure for optical or scanning electron microscopy
(SEM). Martina et al.[72] referred these parameters of wall
width before and after the finishing as total wall width
(TWW) and effective wall width (EWW), respectively.
The multilayer depositions are analyzed to calculate
TWW, EWW, surface waviness, and deposition efficiency.
Apart from the geometrical analysis, it is important to
analyze the microfeatures of deposition through which
post-deposition effects like deposition errors, presence
of defects, inclusions, dilution, etc. can be analyzed in
detail. Jhavar et al.[80] have successfully fabricated AISI
P-20 multilayer deposition consisted of fully dense structure with good surface quality using µ-PTA wire deposition process. Fig. 22A shows the geometry of wall
fabricated by multilayer deposition, Fig. 22B shows the
cross-section of multilayer deposition depicting various
regions for SEM evaluation. Fig. 23 depicts SEM micrographs corresponding to various parameters used to judge
the quality characteristics of multilayer wall deposition.
The deposition above few initial layers was found to be
homogeneous, and the hardness values of these zones
were found near to that of the substrate. The µ-PTA wire
deposition process was able to fabricate straight wall consisting of 15 layers having TWW of 2.45 mm and a EWW
of 2.11 mm with a deposition efficiency of 87%. It could
achieve a maximum deposition rate of 42 g/hr. Results
also proved that µ-PTA wire deposition process to be
Fig. 23 SEM micrographs
representing various parameters
used to judge the quality characteristics of multilayer wall deposition (A) region A in HAZ; (B)
region B 1 mm above the substrate; (C) region C 3 mm above
the substrate; and (D) region D 6
mm above the substrate.
Source: From Jhavar, Jain,
et al.[80] ©2014 Elsevier. Reprinted with permission.
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Fig. 22 Multilayer deposition
by PTA wire deposition process
(A) geometry of the wall fabricated and (B) cross-section
depicting various regions for
SEM evaluation.
Source: From Jhavar, Jain,
et al.[80] ©2014 Elsevier. Reprinted with permission.
736
cost-effective, material efficient, energy efficient, and
environmental friendly process for multilayer deposition
and has the potential to become an alternative ALM process for metallic materials.
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Capabilities and limitations
µ-PTAwire deposition process produces stable and smooth
arc characterized with no sparks. The equipment is also
portable and lightweight with an easy to connect torch and
accessories available allow quick setup. The process is
capable of making fully functional, dense, and highquality additive layer-manufactured jobs. The process was
also found to be energy efficient, environmental friendly,
cost-effective and an alternative to the existing deposition
processes especially because of its capability to produce
low volume deposition. Deposition materials in the form of
wire have nearly 100% deposition efficiency and are less
health hazardous than the powder deposition material.
µ-PTA wire deposition process is limited to materials having
good ductility, as they can be easily formed in wire shapes.
Applications
µ-PTA wire deposition process can be utilized for a wide
range of applications from the addition of delicate features
to the existing components to the making of fully functional components. The process can also be used in repair/
remanufacturing of metallic dies,[81] gears, and high-value
components. Surface modification developed FGMs and
processing of metal matrix composites are the upcoming
applications of µ-PTA wire deposition process. This process finds its applications used in aerospace, avionics,
biomedical, automotive, electronics, special purpose engineering, MEMS, repair of turbine parts, etc.
Metal Deposition: Plasma-Based Processes
µ-PTA Powder Deposition Process
Working principle
Fig. 24 depicts the generation of plasma in the μ-PTA
powder deposition process. The principle of plasma
generation in the μ-PTA powder deposition process is
essentially same as that in the μ-PTA wire deposition
process. The μ-PTA powder deposition process also
work with very low plasma current (generally up to
20 A) which in turn results in comparatively low
energy density and low plasma velocity. The microplasma torch generates plasma arc that creates a melt
pool on the substrate surface and stream of powdered
deposition material is delivered into melt pool. When
the powder contacts the melt pool it is absorbed into
melt pool and creates weld bead. The μ-PTA powder
deposition process can greatly reduce the product
development time by using the concepts and techniques
of CAD/manufacturing, robotics, etc. It has the ability
to manufacture net shape or near-net shape parts of
very complex geometries from high quality metal materials and has potential to become an alternative to the
existing ALM processes.
Capabilities and limitation
In this process, powder deposition of materials is advantageous during low dilution required in deposition, high metallurgical bond, deposition of FGMs, and composite
materials. But it is disadvantageous from the energy and
material utilization point of view. Deposition materials in
the form of wire have nearly 100% deposition efficiency
and less health hazardous than the powder deposition
material.
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Fig. 24 Concept of μ-PTA
powder deposition process.
Metal Deposition: Plasma-Based Processes
737
Table 2 Characteristics of various plasma-based metal deposition processes.
Plasma thermal
spraying
PTA
deposition
µ-PTA
deposition
Chemical reaction
Thermal energy
Thermal energy
Thermal energy
Processed in
atmospheric or
vacuum chamber
Deposition in
atmospheric
with inert gas
Deposition in
atmospheric
with inert gas
Deposition in
atmospheric
with inert gas
Physical
Chemical and
metallurgical
Diffusion
Diffusion
Diffusion
Deposition rate
●
●●
●●●●●
●●●●
●●●
5.
Depositing medium
Molecules and atoms Atoms
Particles
Particles
Particles
6.
Uniformity of coating
●●●●●
●●●●
●
●●
●●●
7.
Heat affected zone
●
●●
●●●
●●●●●
●●●●
8.
Deposition quality
●●●●●
●●●●
●
●●
●●●
9.
Applications
Thin film deposition
of pure metal, alloy,
and refractory
Thin film deposition
of pure metal, alloy,
and refractory
Hard coatings
of metal, alloy,
and refractory
Hard coatings
of metal, alloy,
and refractory
Micro- to milisized hard
coatings
Item
PVD sputtering
1.
Mechanism of deposition
Momentum transfer
2.
Working environment
Processed in
vacuum
chamber
3.
Bond type
4.
PECVD
Note: Lower to higher: ●, ●●, ●●●, ●●●●, and ●●●●●.
Applications
COMPARATIVE EVALUATION
Most of the metallic materials are easily available in powder form rather than wire form because it is difficult to draw
wire of hard, brittle, tough, and high strength materials.
Hence, μ-PTA powder deposition process is particularly
useful for those materials which can be easily powdered
but difficult to be drawn as wire such as nonferrous alloys,
semiconductors, composites, ceramics, FGMs, and shaper
memory materials.
Table 2 presents the comparative summary of various
plasma-based metal deposition processes comparing mechanism of deposition, working environment, bond type,
deposition rate, deposition medium, deposition quality,
HAZ, uniformity of coating, and applications.
Surface modification applications. μ-PTA powder deposition surface cladding is an effective process for performing surface modification on abrasion, wear, and heatsensitive materials. Variety of alloys such as tool steel,
stainless steel, nickel, cobalt, and titanium alloys can be
deposited using μ-PTA powder deposition process.
Repair/remanufacturing. Engineering components and
tools fails before the completion of their expected service
life due to local impacts, thermal stresses, corrosion, erosion, fatigue, and other severe work environment. It is
highly uneconomical to reject such components with minor
defects much before their service life. μ-PTA powder deposition is a cost-effective process for repairing/remanufacturing them.
3-D parts manufacturing. Many industrial applications
require fabrications of free-form surfaces/geometry of the
metallic components. μ-PTA powder deposition process can
be used for manufacturing 3-D parts with fully functional,
complex geometry, long-term end-use products. It can also
be used for strategically add features to forging and casting.
CONCLUSIONS
Plasma-based metal deposition processes are commonly
being used in various industries for various surface engineering applications. The several deposition techniques
such as PVD sputtering, PECVD, plasma thermal spray,
PTA depositions, and m-PTA depositions are discussed in
this entry. Research in the plasma-based deposition processes has rapidly developed new variants to improve the
deposition rate, quality of deposition, and flexibility to use
variety of materials for deposition. This entry highlighted
the newly developed plasma-based processes, their fundamental principles, methodology, advantages, limitations,
and applications.
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