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Black coatings for 304 stainless



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January 24, 2022

Q. We have some stainless steel (17-4PH H900) parts that are coated in a diamond-like-carbon coating (DLC). We recently had the coating coming off after the parts were steam autoclaved. Never have seen it before. It comes off in the form of a powder.

50847-1a   50847-1b

The coating appears to be intact, but puts a black residue on your hands when you touch the parts. Does anyone know why this is happening? Thanks!

Bill White
- Traverse City, Michigan



February 2022

A. Hi Bill. I don't have any actual experience with DLC coatings, but while we await a response from someone who does have such experience, you might investigate the coating thickness. I have read that when it's thicker than about a micron it cracks and powders like this.

Luck & Regards,

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



February 22, 2022

A. Bill,
Your problem is not uncommon. DLC coatings generally have pretty high compressive stresses. Thermal cycling can lead to cohesive failure of the coating, i.e., powdering. Thickness is a big part of the problem, as Ted noted. The thicker the coating, the higher the compressive stress, the more likely it is to happen.

jim treglio portrait
Jim Treglio - scwineryreview.com
PVD Consultant & Wine Lover - San Diego,
California




February 24, 2022

Q. Thanks Jim I appreciate the input. Do you have any additional information you can provide that would help with reducing the residual compressive stresses? Or information that would allow me to detect when a coating will fail under thermal cycling?

Bill White [returning]
- Traverse City, Michigan



March 15, 2022

A. Bill,
To reduce the stress, best to reduce the thickness of the coating and bias on the substrate during coating. This latter will affect that nature of the coating, so reducing the thickness is the better approach.
I recommend a simple test to determine if a coating is going to fail or not. Take coating samples home and put them in your freezer overnight. Next morning hit them with a blow dryer. If the coating stays on, you're probably ok. If not, back to the drawing board...
Jim

jim treglio portrait
Jim Treglio - scwineryreview.com
PVD Consultant & Wine Lover - San Diego,
California






Closely related Q&A's, oldest first:

December 31, 2008

Q. I manufacture a laser cut 304 stainless product that I want to make a "black" or dark finished version for law enforcement. The coating has to be thin and very durable, which is why I am looking for a plated, chemical conversion or some sort or vapor deposition process.

Any ideas and specific recommendations of suppliers for the process?

thanks!

Cary Chleborad
buyer, designer - Sacramento, California, USA



January 5, 2009

A. We offer a "DLC" or Diamond Like Coating that we are currently plating on parts for the military and several major firearm manufacturers..

The coating is seriously durable and beautiful to boot!.

Ryan Cook
Ryan Cook
Toccoa, Georgia



March 6, 2009

A. The available dark/black coat by electroplating and chemical techniques are:

Black Nickel Electroplating , Black Chromium, Black Tin-Nickel Alloy, Black Tin-Cobalt Alloy, Black Colored Zinc electroplating, Electroless Black Nickel.

Gabriel Schonwald
Bnei Berak, Israel



April 17, 2009

A. Try Melonite QPQ. It can produce the finish you're looking for.

Bill Melvin
- London, Ohio



April 17, 2009

A. Hi Cary. For more info about QPQ, please see our on-line article on the Kolene QPQ process

Regards,

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




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