ZrN (zirconium nitride) coatings

A. Hello Christophe!

ZrN is a commonly applied physical vapor deposition coating. When done right it looks like gold in color, and is more wear resistant even though it is quite thin (about 2 to 5 microns). I know Richter Precision does this process, and can tell you a lot more about it. Do a search on "PVD coatings" and you'll likely find others.

Good luck!

A. ZrN is a hard coating, somewhat harder than TiN, but otherwise very similar in nature. It is used on cutting tools, but to a lesser degree than TiN, as it is somewhat more expensive to deposit. It is better than TiN for decorative purposes -- much closer in color to gold, and provides better corrosion resistance. By adding a little carbon, you can achieve a brass color. The gold drills sold at Sears are ZrN coated, as are many high-priced faucets and door knobs.

A. Hi Michele. Titanium nitride and zirconium nitride are not applied by electroplating. They are applied by PVD processes (gaseous processes) in a vacuum chamber. However, it is often desirable or necessary to include an electroplated underplate--perhaps nickel plating--underneath the PVD coating.

A. Just to add to the previous response, it depends very much on what you are looking for in a finish. For decorative coating purposes, a thin ZrN is usually deposited over electroless nickel, sometimes with a hard chrome interface. For wear applications, a much thicker ZrN coating is applied directly on the substrate. As the ZrN is deposited by PVD, there is no waste stream.

A. Ted is correct that an electroplated layer is needed. TiN and ZrN like coatings are noble in nature and will cause severe corrosion in steels if applied directly. You need to seal the steel similar to that in decorative chrome. These need to be applied as the final finish. Also, severe difference in thermal expansion coefficient will result in cracking of nitrides if applied directly. Depending on size and shape, there may be a limitation where it can be applied.

Question: Are the blades sitting on the shelf before cleaning, or after cleaning, i.e., do you see the black residue after you have removed them from the sterilization pouch?

A. The coating was likely deposited by cathodic arc. In this process, an intense arc is formed on the target that locally evaporates and ionizes the metal. It also forms a pool of molten metal on the surface. The pool spits out droplets of molten metal which land on the substrate and solidify. These macro-particles might be what you are seeing.

A. It depends on many factors- type of PVD - cathodic arc or sputtering, operating pressure, number of objects you need to coat in a batch, jigs you are using etc. Generally for cathodic arc distance is not too critical. If the operating pressure is too high the ions/atoms coming from the PVD source would get scattered and the flux on the substrates could be considerably reduced. I had encountered this problem while sputtering gold and had to keep the distance less than 50 mm.It is for the operator to optimise the distance unless the manufacturer of the machine has specified it.

A. Physical vapour deposition has different versions and the one you are using is the oldest one. For a single 10 mm substrate distance is not critical unless you are too close to the tungsten boat.A distance of 10 - 20 cm should be good enough. Larger the distance lower will be deposition rate which falls as the square of the distance. You would not get a uniform coating on all surfaces if that is what you are looking for irrespective of the distance.

 Dear H. R. Prabhakara,

Thank you for your detailed description. I understand you meant when the the electron gun's being used.

As this project's for surface empowerment of a drill, not a precision coat as with the optical filters are required. I'm hence using the thermal evaporator boat.

I will test the distance you mentioned and will update you with results; probably post the result images here if would be possible.

Best,
Shahab

And special thanks to Ted for this rich environment where we are able to collaborate!