PVD for decorative applications Lesson 4: Coating color range in decorative PVD

Mostly deposited with CAE. The high ionization rate of the technology makes it possible to tune the color very sensitively, by adding reactive gases like nitrogen, acetylene or oxygen to metals like titanium or zirconium. A higher nitrogen content, for example, will result in a brighter gold, whereas a higher acetylene content results in a more copperish color.

These days, HiPIMS (although it is a type of MS, not a type of CAE) also allows us to reach these colors, because it can attain comparable ionization rates. HiPIMS coatings are higher quality in several important ways: they exhibit lower roughness and defect density. However, as described earlier, HiPIMS deposition rates are lower and the investment cost is very high, which makes it a more premium solution.

Ranging from bright silver to dark black, you can choose between CAE and MS. For the very light colors, CAE is the better choice, whereas dark black is only reachable with MS. The coating characteristics matter too, for grayscale applications.

A very rough black coating, like you would get with CAE, can be very sensitive to fingerprints and have a milky appearance. MS black coatings, in contrast, are mostly very soft and cannot be used for more hard-wearing applications.

The same applies for the so-called interference colors, which include blue, purple, green and rainbow colors. These can also be deposited by both CAE and MS, using various coating materials in mostly oxide compounds.

The biggest challenge arises from the fact that the final color of the coating depends on the thickness of the coating, because interference colors arise when polarized light moves through a surface. Especially when coating 3D parts, you need very good process control to achieve a homogeneous color result.