Physial vapor deposition (PVD) is a generic term for vacuum plating processes involving bombardment of the surface by energetic ions to enhance coating adhesion and improve coating structure.
It is a common industrial process. One of the early applications was to apply very hard metal nitride coatings to cutting tools to extend tool life. The process has since been modified to provide a wide variety of coatings that are hard, wear resistant, and decorative. Today, metal nitrides such as titanium nitride (TiN) zirconium nitride (ZrN) and chromium nitride (CrN) are applied on faucets, door hardware, lighting fixtures, and a wide variety of other surfaces where long lasting finishes are desired.
The process used by AMP&P is a common form of PVD called cathodic arc PVD, or CA-PVD. Our process begins by putting the parts in a vacuum chamber and heating them up to modest temperatures to drive water vapor off of the surfaces (it can effect the coating adhesion and color). The chamber is backfilled with gases, usually argon and nitrogen. We then draw an arc on a metal cylinder in the center of the chamber. The arc is so intense on the metal surface that it pulls metal atoms off of the surface and strips off some of their electrons, forming a metal ion plasma. An electric field applied to the parts pulls the metal out of the plasma onto the surfaces with such force that they are metallurgically bonded to the part, where they react with the nitrogen to form the desired nitride.
If the metal is titanium, the resultant coating, TiN, is dark gold. If the metal is zirconium, the resultant coating, ZrN, is light gold. Chromium yields a silvery-colored CrN. A wide variety of colors can be achieved by adding other gases during the deposition, such as oxygen and acetylene.
PVD coatings are too thin to affect part tolerances, and in general will reflect the surface roughness of the base material. However, it is often necessary to plate the part surface with nickel and chromium prior to applying the PVD coatings. The combination can be thick enough to affect tolerances.
PVD coatings can be deposited on most metals, though some require a base of nickel and chromium.
- Stainless steel.
Stainless steel parts are normally coated without any base layers.
While it is easy to apply PVD coatings to steel, steel components are more often nickel/chrome electroplated before PVD processing for better corrosion resistance.
- Brass and copper.
As with steel, it is common to nickel/chrome plate copper and brass before PVD coating to provide better corrosion resistance.