Content area
Full text
Physical vapor deposition describes a specific category of thin-film vacuum coating processes. The definition of PVD coating can be broken down as follows:
* Physical-Individual atoms and molecules are physically liberated from the source of the pure "donor" material, known as the source or target.
* Vapor-The physical atoms and molecules are vaporized in a vacuum vessel.
* Deposition-The vapor is deposited in a microscopically thin layer onto substrates that share the space in the vacuum vessel. The presence of reactive gases such as nitrogen, oxygen, or hydrocarbons result in nitrides, oxides, or carbides of the target material being formed by chemical reactions between the vaporized metal atoms and the reactive gas species.
The most common of these thinfilm vacuum coating processes include evaporation (e.g., using a cathodic arc or thermal technique), ion beam deposition, and sputtering (e.g., using plasmas). All PVD coating processes must occur inside a vacuum chamber so that the vaporized materials do not react with any atmospheric contaminants that could interfere with the microscopic layer of coating, or with the adhesion of the growing thin film to the substrate. In the specific case of cathodic arc, the vaporization occurs as a direct result of the application of an electrical arc to the surface of the target.
Functional vs. Decorative
The two main subcategories of this type of coating are functional and decorative hardcoatings. While they are often made of the same materials, both types may be applied using different thickness specifications to optimize them for a specific application. Functional hardcoatings are used to impart properties such as scratch resistance, toughness, thermal protection, environmental stability/corrosion resistance, friction reduction, and wear reduction.
Decorative hardcoatings are used to impart color to substrates. One example of this is in the use of different colored coatings on metallic shims of different thicknesses, which allow quick and reliable visual recognition in a busy assembly area. Likewise, some surgical scalpels are decoratively hardcoated for ease of blade size identification in surgical units.
Some hardcoatings serve the dual purpose of both decorative and functional coatings. Architectural window glass is a good example of this...