Summary for black coatings for stainless Discussion
Black coatings for 304 stainless are discussed in the context of a DLC-coated 17-4PH H900 part that began shedding a black powder after steam autoclaving. Bill White asked why the coating seemed intact but left residue on hands. Jim Treglio suggested checking coating thickness, noting he had read that DLC thicker than about one micron can crack and powder. Gabriel Schonwald listed several alternative dark finishes available by electroplating or chemical methods, including black nickel, black chromium, black tin-nickel, black tin-cobalt, black zinc, and electroless black nickel. Bill Melvin suggested Melonite QPQ as a possible finish for the desired look. The thread does not identify a single confirmed cause, but it points to excessive DLC thickness as a likely issue and offers several alternative black finishing processes to consider.
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.
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
January 24, 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,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
February 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 – scwineryreview.com
PVD Consultant & Wine Lover
San Diego, California
February 22, 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
February 24, 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 – scwineryreview.com
PVD Consultant & Wine Lover
San Diego, California
March 15, 2022
⇩ Similar, related, Q&As — oldest first ⇩
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
December 31, 2008
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
Toccoa, Georgia
January 5, 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
March 6, 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, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
April 17, 2009
adv.
