Physical Vapour Deposition Coating

What is Coating?

The covering or spreading of a layer of a material on the component surface is called coating. Since every object expected to meet Variety of specification which could be conflicting with each other. To overcome this problem coating is utilized.

Various Methods of Coating or Coating Deposition:

• Spray Deposition Process.
• Chemical Vapour Deposition Process.
• Physical Vapour Deposition Process.

Here, in this topic we will see Physical Vapour Deposition Process.

PVD:

PVD stands for Physical Vapour Deposition. This method utilizes vacuum technology. PVD is the technology of using physical way to coat materials on to the substrates in the condition of vacuum.

PVD Process Description:

Above figure explains the PVD coating method in brief. Initial and final phase is called as condensed phase and final phase is achieved through the series of phases and process like, gaseous, evaporation and condensation respectively.

Electron Beam Physical Vapour Deposition:

Electron Beam Physical Vapor Deposition is also called as EB PVD process. EB-PVD is a derivative of the electron beam melting technique.

EB-PVD is a form of PVD in which a target anode is bombarded with an electron beam given off by a electron gun under high vacuum.

EB-PVD offers high flexibility in depositing ceramic and metallic.
EBPVD is a relatively new material coating method that produces good results. It is particularly useful in thermal barrier coatings in aircraft turbine blades and in protective coatings on cutting tools.
The increased deposition rates and variety of materials and techniques of the EBPVD process provide an opportunity to broaden the application of this technology into the marketplaces.

Advantages of EB-PVD:

1. The deposition rate in this process can be as low as 1 nm per minute to as high as few micrometers per minute.
2. The deposit has a columnar grains structure.
3. Smooth surface, better interaction with the substrate.
4. The EB-PVD process offers extensive possibilities for controlling variations in the structure.
5. Relatively high deposition rates.

Applications of EB-PVD Coating:

EB-PVD coating have two kinds of major applications which are 1. Decorative Coating. and 2. Tool Coating.

Decorative Coating Applications:

1. For decorative application ,gold is deposited after depositing TIN.
2. The system has also been used for coating of telescopic mirrors.

Applications of PVD in Turbine Industry:

1. To improve life or work temperature of blades.They are coated by the use of thermal barrier coatings (TBCs) over metallic substrate.
2. TBC is the thermal insulator.
3. Zirconia is used as ceramic layer.
4. Tablets of an alloy of Ni, Cr and Al are evaporated using the energy of an electron beam and then condensed on the substrate.

Applications in Machine Tool and Forging Die Industries:

1. Metallic carbides, nitrides, and oxides have long been known to be very hard, wear resistant materials.
2. Applying these hard coatings to tool steels and tungsten carbide-cobalt cutting inserts can increase the tool life by high percent.

Limitations of Physical Vapour Deposition Coating:

1. The process is expensive.
2. Possible to coat only outer surface of complex geometries.
3. At present the process is dependent on highly trained users.
4. Filament degradation in the electron gun.