A wide range of colors achievable with PVD technology!
Decorative coatings by Physical Vapour Deposition (PVD) satisfy increasingly stringent demands such as
attractive but accurately uniform color
high hardness
wear resistance
stability of coated color over time
corrosion resistance
and uniform over 3-D objects
In fact, quality requirements are ameliorate while production costs are always in decline.
Among all the possibilities of PVD deposition, rectangular cathodic arc and magnetron sputtering certainly plays a critical role, presenting many advantages over the rest of methods.
One among the biggest advantage by decorative PVD is the low deposition temperature (typically < 160°C) offer the possibility to coat the substrates which has the less thermal-resistance (plastics, thin metal springs, porous materials etc).
PVD process offers more and more colors in the recent years owing to the improvements in arc or magnetron design equipped with
variable and differential magnetic field
extra cooling of targets
and auxiliaries allow multiple gas flow options much closer to the target
cathode poisoned on axis of the rotating substrate table
and 3-D rotation of satellite spindles that can go 45 rotations per one full rotation of substrate axis.
Among all other colors, the most challenging colors are
brown
rosegold
purple
bronze.
The reason is: these colors are involving oxygen in their process, which add complication to the plasma uniformity.
If you need uniform color over the vertical height or in the curvature of 3-D parts, uniformity of plasma density is mandatory.
Titanium target operated at nitrogen atmosphere and Chromium operated at full acetylene gas load would never create issues in uniformity as breaking of nitrogen molecules and acetylene molecules are not so easy.
Hence, the gradient in the plasma potential would be too low as most of the energy would be spent breaking the reactive gas molecules.
However, that’s not the case for oxygen, an easily ionizing with subsequent recombination.
Hence maintenance of plasma density throughout vertical and horizontal profile of the substrate table is challenging.
People try multiple ways: either the single or the combination of the following ways
magnetic field variation
gas feed
3-D rotation of parts
High density plasma
Central cathode
Central cathode is not so favorable owing to the production and maintenance costs.
If you would like to know more about how to achieving the color uniformity for brown, purple, bronze and rosegold, please do not hesitate to contact me on cpernagidis@avaluxe.de