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PVD (Physical Vapor Deposition)

PVD coating has become the premier alternative surface treatment for many of the hard-chrome or electro-chemical surface treatment methods of the past, simply for its improved functionality, increased durability, increased lifetime, as well as its environmental friendliness. We will get into the actual process of PVD coating later.



SURFACE ENGINEERING

"Surface engineering involves changing the properties of the surface and near-surface region in a desirable way. Surface engineering can involve an overlay process or a surface modification process. In overlay processes a material is added to the surface and the underlying substrate (material to be coated) is covered and not detectable on the surface. A surface modification process changes the properties of the surface but the substrate material is still present on the surface." (Mattox 29) There are many different processes that can be utilized in order to obtain certain surface characteristics. Examples of these methods can be seen below in Table 1-1.

(Mattox 30)



All of the processes have unique pros and cons to different applications. Sometimes the surface of a substrate (material to be coated) may be modified to change or enhance properties of the coating. A couple examples are before you hard coat steel by Physical Vapor Deposition (PVD) you would harden the surface by plasma nitriding or before sputtering. While coating a turbine blade in a jet engine one would shot peen it to increase its compressive strength and increase the density of the coating.

During the atomic film deposition process, the coating material is deposited one atom at a time. The film remaining at the end of the coating process can vary from a crystalline form to amorphous with varying densities. This film is only a few microns thick normally ranging from 2-5? and normally given the name "thin film." If you are unfamiliar with the metric system or Système International (SI), review Table 1-2 and 1-3 below.

PHYSICAL VAPOR DEPOSITION (PVD) PROCESSES

The process of thin film coating by means of PVD is to apply electric current and voltage or bombardment of inert gas to ionize the desire material. Once the material is ionized into vapor form it is the deposited on the desired substrate. There are several general types of PVD coating Sputtering, Vacuum Evaporation, Ion plating and IBAD.

www.pvd-coatings.co.uk*
Please click above for more illustrative information regarding the theories behind various PVD coating deposition methods.

Table 1-2. PVD processing techniques: (1a) vacuum evaporation, (1b and 1c) sputter deposition in a plasma environment, (1d) sputter deposition in a vacuum, (1e) ion plating in a plasma environment with a thermal evaporation source, (1f) ion plating with a sputtering source, (1g) ion plating with an arc vaporization source and, (1h) Ion Beam Assisted Deposition (IBAD) with a thermal evaporation source and ion bombardment from an ion gun (Mattox 32).

VACUUM DEPOSITION

Vacuum evaporation is also known as vacuum deposition and this is the process where the material used for coating is thermally vaporized and then proceeds by potential differences to the substrate with little or no collisions with gas molecules. A common term for the trajectory for this type of deposition is "line of sight." By running this process under a vacuum, contamination by other gases is greatly reduced. Normal vacuum levels are in the medium to high vacuum range of 10-5 to 10-9 Torr. Depending on the gas contamination of the vacuum chamber, the deposition rate can be much higher when compared to the other methods. Thermal evaporation is normally done by resistive coils or a high energy electron beam. The substrates have a larger distant from the source in order to reduce radiant heat transfer. "Vacuum deposition is used to form optical interference coatings, mirror coatings, decorative coatings, permeation barrier films on flexible packaging materials, electronically conducting films, wear resistant coatings, and corrosion protective coatings." (Mattox 33)

SPUTTER DEPOSITION

Sputter deposition, otherwise known as sputtering, is the process where the material is not thermally vaporized and the atoms are physically redirected from the source material to the substrate by collision from a bombarding particle. The distant from the source to the substrate is much shorter than that of vacuum deposition. Sputter can also be done under a higher plasma pressure of 5-20 mTorr and the material is heated by collisions with gas molecules. The sputtering source itself can be made of elements, alloys, mixtures, or compounds. Titanium Nitride (TiN) and Zirconium Nitride (ZrN) along with some Boron mixed Diamond-like carbon (DLC) are common coatings for this process. This form of deposition is commonly used in semiconductor manufacturing, on architectural glass, reflective coatings, compact discs (CDs), magnetic films, dry film lubricants, and decorative coatings.

ARC VAPOR DEPOSITION

"Arc vapor deposition...uses a high current, low-voltage arc to vaporize a cathodic electrode (cathodic arc) or anodic electrode (anodic arc) and deposit the vaporized material on a substrate. The vaporized material is highly ionized and usually the substrate is biased so as to accelerate the ions ("film ions") to the substrate surface." (Mattox 34)

ION PLATING

Ion Assisted Deposition (IAD) or Ion Vapor Deposition (IVD) otherwise known as Ion Plating (IP) is a deposition process that utilizes periodic or concurrent bombardment of the depositing material in order to control or modify the properties of the film. "In ion plating the energy, flux, and mass of the bombarding species along with the ratio of bombarding particles to depositing particles are important processing variables." (Mattox 34) The material may be vaporized by chemical vapor decomposition, sputtering, or evaporation. This process can be done where ions for bombardment are received from a separate ion gun or from the plasma itself. The separate ion gun process is sometimes known as Ion Beam Assisted Deposition (IBAD). "Ion plating is used to deposit hard coatings of compound materials, adherent metal coatings, optical coatings with high densities, and conformal coatings on complex surfaces." (Mattox 34)


*This website is in no way affiliated with Eclat Coating Inc. We merely wish to provide our customers with as much additional information as possible regarding PVD Coating.

Bibliography

1. Mattox, Donald M. Handbook of Physical Vapor Deposition (PVD) Processing: Film Formation, Adhesion, Surface Preparation, and Contamination Control.  New York: Noyes Data Corporation/Noyes Publishing, 1998.

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