Something about PVD coating knowledge
What is PVD?
Physical vapor deposition (PVD) describes a variety of vacuum deposition methods which can be used to produce thin films and coatings. PVD is characterized by a process in which the material goes from a condensed phase to a vapor phase and then back to a thin film condensed phase.
Examples
1. Cathodic Arc Deposition: In which a high-power electric arc discharged at the target (source) material blasts away some into highly ionized vapor to be deposited onto the workpiece.
2. Evaporative deposition: In which the material to be deposited is heated to a high vapor pressure by electrical resistance heating in "high" vacuum.
3. Sputter deposition: In which a glow plasma discharge (usually localized around the "target" by a magnet) bombards the material sputtering some away as a vapor for subsequent deposition.
Various thin film characterisation techniques can be used to measure the physical properties of PVD coatings, such as:
Calo tester: coating thickness test
Nanoindentation: hardness test for thin-film coatings
Pin on disc tester: wear and friction coefficient test
Scratch tester: coating adhesion test
X-ray micro-analyzer: investigation of structural features and heterogeneity of elemental composition for the growth surfaces
Comparison to other deposition techniques
Advantages
PVD coatings are sometimes harder and more corrosion resistant than coatings applied by the electroplating process. Most coatings have high temperature and good impact strength, excellent abrasion resistance and are so durable that protective topcoats are almost never necessary.
Ability to utilize virtually any type of inorganic and some organic coating materials on an equally diverse group of substrates and surfaces using a wide variety of finishes.
More environmentally friendly than traditional coating processes such as electroplating and painting.
More than one technique can be used to deposit a given film.
Applications
As mentioned previously, PVD coatings are generally used to improve hardness, wear resistance and oxidation resistance. Thus, such coatings are used in a wide range of applications such as:
Aerospace
Automotive
Dies and moulds for all manner of material processing
Cutting tools
Firearms
Optics
Watches
Thin films (window tint, food packaging, etc.)
Darts barrels
Metals (aluminium, copper, bronze, etc.)
Decorative applications
By varying the gases and duration of process, a range of colours are produced by Physical Vapour Deposition on stainless steel. The resulting coloured stainless steel product can appear as brass, bronze and other metals or alloys. This PVD coloured stainless steel can be used as exterior cladding for buildings and structures, such as the Vessel sculpture in New York City and The Bund in Shanghai. It is also used for interior hardware, panelling and fixtures.
Cathodic arc deposition
Cathodic arc deposition or Arc-PVD is a physical vapor deposition technique in which an electric arc is used to vaporize material from a cathode target. The vaporized material then condenses on a substrate, forming a thin film. The technique can be used to deposit metallic, ceramic, and composite films.
Sputter deposition
Sputter deposition is a physical vapor deposition (PVD) method of thin film deposition by sputtering. This involves ejecting material from a "target" that is a source onto a "substrate" such as a silicon wafer. Resputtering is re-emission of the deposited material during the deposition process by ion or atom bombardment. Sputtered atoms ejected from the target have a wide energy distribution, typically up to tens of eV (100,000 K). The sputtered ions (typically only a small fraction of the ejected particles are ionized — on the order of 1 percent) can ballistically fly from the target in straight lines and impact energetically on the substrates or vacuum chamber (causing resputtering). Alternatively, at higher gas pressures, the ions collide with the gas atoms that act as a moderator and move diffusively, reaching the substrates or vacuum chamber wall and condensing after undergoing a random walk. The entire range from high-energy ballistic impact to low-energy thermalized motion is accessible by changing the background gas pressure. The sputtering gas is often an inert gas such as argon. For efficient momentum transfer, the atomic weight of the sputtering gas should be close to the atomic weight of the target, so for sputtering light elements neon is preferable, while for heavy elements krypton or xenon are used. Reactive gases can also be used to sputter compounds. The compound can be formed on the target surface, in-flight or on the substrate depending on the process parameters. The availability of many parameters that control sputter deposition make it a complex process, but also allow experts a large degree of control over the growth and microstructure of the film.
Evaporation (deposition)
Thermal evaporation in a resistive heated boat
Evaporation is a common method of thin-film deposition. The source material is evaporated in a vacuum. The vacuum allows vapor particles to travel directly to the target object (substrate), where they condense back to a solid state. Evaporation is used in microfabrication, and to make macro-scale products such as metallized plastic film.
