How to achieve a Black PVD finish

A. I did finally get a great black coating by cathodic arc using chromium targets, acetylene and nitrogen gas, and pulsing the bias at >20,000 pulses per second. We had some success with Ti targets as well, but it is hard to control the compressive stress in the coating.

A. Hi Shahid. Jim's posting gave excellent hints towards getting started, and left open problems like hard to control compressive stress. Please tell us what you have tried and what you have learned from your efforts. Thanks!
Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Hi,

Jet black colour can be obtained as DLC coating. What application system do you have ?

A. We actually produced a great black in one of our production systems about two years ago. We weren't trying to get a black coating -- we had a wee bit of an accident. I had a friend try to duplicate our coating. He did -- but couldn't do it consistently.

The closest to black PVD coating that can be deposited consistently by cathodic arc is AlTiN (60% Al). Unfortunately, AlTi targets with 60% Al are very expensive.

? Can we assume you are using a mix of nitrogen and acetylene, Iztok? What ratio and what color are you getting? Thanks :-)

A. I think you should use carbon gas. TiAlCN coatings are bright black colour, but I haven't tried it.

A. We've tried adding hydrocarbon gas to TiAlN. You get dark gray, but not black. I've got a friend that can deposit a black coating, but he has some special equipment so we send parts to him for coating.

A. I can actually get a black finish with PVD TiAlN (~5% reflectivity on the whole visible range) but the reproducibility of the process is an issue. Even keeping all the parameters unchanged I get sometimes a very nice black finish and sometimes a metallic-grey surface. I suppose some contamination in the plasma due to desorption from the vacuum chamber but for lack of a Mass spectrometer I couldn't prove it quantitatively up to now. Has someone similar problems?

A. It is possible to achieve black.

Black to dark grey transitions may be in part due to the surface finish, as the polish increases the better the aspect of the black.

We are now in a quest to achieve white, using our CAPVD chamber.

A. Hi Araz. I know very little about PVD, so someone else will have to take it further, but "rainbows", whether desired or undesired, and regardless of what substrate or what coating method, are invariably caused by a partial wavelength transparent/translucent coating ...

... Some of the light bounces off the surface of the coating and some of it -- after traveling very slightly further -- bounces off the surface of the article. As the light reflects back, the two halves interfere with each other canceling some wavelengths and augmenting others. The coating causing the rainbow can be due to oil, as in the rainbows we may see on a mud puddle, or your PVD coating being translucent and thin.

Regards,

A. Ted has explained it well. This effect is called interference of light waves. The situation is further complicated by variation in film thickness and the viewing angle as they determine the optical path difference travelled by rays of light reflected from the top and bottom surfaces. In the present case, depending on the type of fixture, coating thickness can decrease close to the substrate holder due to shadowing effect causing rainbow effect.
I may add that in an actual rainbow origin of colours is due to a different effect namely refraction of light (through tiny water droplets in the sky) and not interference.

A. I was able to produce a jet black PVD coating using arc technology. However, it entailed changes to the deposition system and a rather complex coating recipe.