Expert: Daniel Mazur - 8/19/2005

Question
What is the process for TiN coating on stainless steel watch straps & How the coating adhesion can be improved?

Answer
Hi,

the most common process used for TiN coatings in industry is the reactive cathodic arc plasma deposition. The idea is that you put a Titanium cathode (or "target", that's the lingo for your source of metal particles) and the stainless piece you want to coat in a vacuum chamber with dilute Nitroen gas. High voltage on the cathode creates nitrogen ion plasma. These ions hit the cathode and sputter the Ti atoms (or clusters of atoms) into space. These particles land on the stainless piece you want to coat and there, on the surface, they react with the nitrogen ions to form TiN.

The adhesion is dependent on several factors: surface cleanlinness, purity of the cathode material and the Nitrogen used, vacuum hygiene of the deposition chamber overall, nitrogen gas pressure, energy of Nitrogen ions, when they hit the surface, the temperature of the stainess piece and the thickness of the TiN coating, to name the most important ones.

I have some experience with a similar deposition, but I am no specialist in TiN to give you the "numbers", the precise parameter values of a successful deposition. Even if I was, every deposition instrument has its own properties, so that fine tuning of the parameters would be necessary either way. By playing with the deposition conditions listed above you can improve the adhesion. You can find plenty of articles on this in scientific journals (Journal of Vacuum Science and Technology, for example).

I hope this answer helps you.

Good Luck!
Daniel Mazur