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Title: Engineering Chemistry
Description: This is specially for 1st and 2nd year students.This will explain you clearly about these processes. It consists information about Thin film coatings,like PVD (physical vapor deposition) and CVD (chemical vapor deposition). Do download it for learning.
Description: This is specially for 1st and 2nd year students.This will explain you clearly about these processes. It consists information about Thin film coatings,like PVD (physical vapor deposition) and CVD (chemical vapor deposition). Do download it for learning.
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60ÛC
...
Pb-Sn or Pb-Sb alloy coated with
PbO2 is used as anode
...
Thin film coatings
It is the process of depositing some materials over solid surfaces
...
This is a process of
depositing some material by atom by atom or molecule by molecule or ion
by ion
...
All these processes are performed in vacuum systems
...
In
this method the metal to be coated is placed in a refractory metal boat or
crucible
...
The contents after melting form an electron
cloud in the shape of ice cream cone with the tip of the cone at the source
...
This process is
widely used to produce decorative coatings on plastic parts those are
resembling shiny metal
...
A lacquer coating is applied over the decorative
coating to provide corrosion protection
...
These coatings are
not normally used by average machine designers
...
For decorative coatings or coatings on optics,
thermal evaporation may be the best suitable for engineering processes
...
The substance to be coated
is connected to a high voltage dc power supply
...
On energizing
current supply, plasma is established between the work and the material to
be coated
...
22
Fig
...
Direct current sputtering is used when the target is electrically conductive
...
A third variation of the PVD process is ion plating, which involves the
evaporation
...
Sputter and ion plated coatings are used in design for very thin films for
electrical, optical and wear-resistant applications
...
The face of a fast wearing tool can be reduced by increasing abrasion
resistance by applying TiN coating
...
But we have to determine whether they adhere to a particular
substrate or not
...
The latter
coatings are also called amorphous hydrogenated carbon coatings, since they
have 30% hydrogen as this is produced from hydrocarbon gas
...
These are applied to give
extra hardness to a substrate
...
The closed
coatings are often preferred for many tool applications
...
Eg
...
Sputtered coating processes produce microscopic modules of diameter of
several micrometers and they are called macros
...
On the other hand they are
usually beneficial to cutting tools
...
The high temperature processes usually produce optimum coating
properties
...
But it is not required
...
The compound decomposes to a metal when it comes in
contact with a substrate at some high temperature
...
Nickel is deposited from nickel carbonyl
...
5mm at the rate of 0
...
This coating finds
application on glass containers to make explosion or shatter resistant glasses
...
All surfaces in the reaction chamber get coated
...
Separate process and reaction must be developed for each
coating
...
But greatest
disadvantage is temperature should be very high at 700ÛC
...
Fig
...
A CVD system
A newer process known as plasma assisted chemical vapour
deposition
...
Some of the coatings may be conducting at very low temperature
...
Chemical Vapour Deposition is used to produce bulk
shapes of high purity silicon carbide
...
Thin-film coatings are key to the manufacture of many electronic
devices
...
Thermal evaporation is a low cost process, but all
these processes are normally batch processes because of vacuum chamber
requirements
...
The molten droplets splat cool on
impact with the substrate and the coating is eventually formed by
overlapping splats
...
The latter can considered to be coating defects, but porosity is
inherent in all the nonfusion processes
...
The high-velocity processes produce the lowest amount
of porosity
...
Some are atomic interaction and others are mechanical interlocking
...
There
is no technical thickness limit
...
5 mm
...
The molten drops are
propelled by a gas at the substrate
Plasma arc spraying
Powder is melted by an arc-generated
plasma within the gun
...
High velocity oxy fuel
Powder is melted in a combustion chamber
containing oxygen, hydrogen and a fuel gas
like methane
...
The source of heat in
plasma spraying is the plasma with a temperature of over 16,650ÛC
compared with only about 2760ÛC for an oxy acetylene flame
...
It is more suitable for spraying ceramics
...
There is very
little heating of the substrate and temperature does not exceed 150ÛC
...
Thermal spraying of metals and ceramics is useful for part buildups and for
producing wear resistant surfaces
...
Fig
...
Nonfusion processes: flame and plasma spraying
High melting thermal spray processes such as High Velocity Oxy fuel
method and detonation gun coating serve the same function as the plasma
process, but they usually have better bond strength and lower porosity
...
Tanks and large equipments plated with zinc or aluminum can be used to
protect very large structure from atmospheric rusting
...
A thermal sprayed zinc
coating of 125µm can keep a bridge rust free for 30 years
...
In ion implantation ions of specific element with
sufficient energy are impinged on the surface of a material with sufficient
energy
...
This process is performed in a vacuum chamber
...
It is done by passing the gas through an electron beam or
plasma
...
The ions are accelerated by an applied
magnetic field
...
The surface of the
metal is hardened by creating atomic defects or misfits by the impinged ions
...
1µm
...
Nitrogen, carbon, boron and chromium are the common implants employed
...
Implantation is normally performed on hard
materials like tool steel to improve wear or related properties
...
Part heating is minimal with no
parts getting more than 148ÛC
...
Implantation would not guarantee improved performance
...
13 Ion implantation
28
Laser and electron beam treatment of surfaces are performed to alter surface
properties by rapid heating and cooling
...
An
amorphous structure is formed if the rate of cooling is above 106ÛC per
second
...
The surface properties of these
glazed surfaces can be significantly different from the properties of the bulk
material
...
Surface alloying can be produced by using laser or electron beam
...
Eg
...
The alloy depth is only a few micrometers
...
This is a very powerful
surface engineering tool
...
It may
be to improve corrosion resistance or appearance or wear resistance or cost
reduction or other purposes
...
For selecting the process the next step is to use a coating or a
treatment that does not alter dimension
...
Ion implantation, selective hardening, diffusion treatment, laser
glazing and the like do not apply a material to the original surface
...
The selection of the
process mainly depends on the following
...
05 to 0
...
0
...
5 to 2
...
5 to 1
Heavy 2
...
0
Gold
0
...
1
Nickel (Soft)
0
...
5
(hard)
0
...
5
Heavy 2 to 50
Silver
Zinc
0
...
3
0
...
5
Approximate
Hardness
(kg/mm2)
Applications
900
Decorative surfaces
wear parts
150
Conductive surface
underplating
Electrical contacts
Atmospheric corrosion
resistance durable
surfaces
80
250
500
100
100
Galling resistance
Rust protection on steel
30
Typical
thickness (mils)
Electroless nickel 0
...
5 to 1
Conversion Coatings
Anodizing
0
...
6
Hardcoating
1 to 3
Phosphate/
Chromate
0
...
4
Black oxide
0
...
1
Thin Film Coatings
PVD TiN/TiCN
0
...
1
PVD Pure Metals 0
...
01
Hardfacing
ERCoCr-A
100 to 200
(cobalt base)
420 stainless steel
100 to 200
RFeCr-Al
125 to 250
(iron/chromium)
Thermal spray Coatings
Tungsten Carbide
3 to 5
(WC/Co)
Chromium oxide
3 to 5
420 Stainless steel
5 to 10
Diffusion Treatments
Carburizing
2 to 60
Nitriding
1 to 30
TiC/VC
0
...
1
Selective hardening
Laser/EB
2 to 30
Flame Hardening
60 to 250
Approximate
Hardness
(kg/mm2)
Applications
450 as plated Atomospheric corrosion
650 aged resistance, wear surfaces
1100
1100
150
800 to 1800
-
Corrosion protection
Abrasion resistance
Improved rust
Resistance
Appearance
Abrasion resistance
Decorative
420
Galling/corrosion
550
650
Corrosion/wear
High stress abrasion
1500
Wear surface
1800
550
Wear surface
Build up
600
900
2000
700
600
Wear Surfaces
Wear Surfaces
Wear Surfaces
Thin Wear Surfaces
Wear surfaces on
large parts
31
Induction hardening
10 to 80
Typical
thickness (mils)
600
Approximate
Hardness (kg/mm2)
Other treatments
Paints
1 to 3
Repair Cements
50 to 200
Dry film lubricants
1 to 2
Ion implantation 0
...
006
-
Laser/EB Glazing
CVD coatings
-
5 to 10
0
...
1
Small parts
Applications
Corrosion protection
Corrosive wear
Sliding systems
Corrosion protection,
wear surfaces
Title: Engineering Chemistry
Description: This is specially for 1st and 2nd year students.This will explain you clearly about these processes. It consists information about Thin film coatings,like PVD (physical vapor deposition) and CVD (chemical vapor deposition). Do download it for learning.
Description: This is specially for 1st and 2nd year students.This will explain you clearly about these processes. It consists information about Thin film coatings,like PVD (physical vapor deposition) and CVD (chemical vapor deposition). Do download it for learning.