Amorphous Carbon Film Coating
Amorphous Carbon Film Coating
(OP)
We're working with a piece of 17-4 PH stainless steel which is annealed. We had applied one coat of metal containing hydrogenated amorphous carbon film to the steel. The vendor then, without consenting us, coated the steel again; but this time with a hydrogenated amorphous carbon film (containing no metal).
My question is, by them doing this, will the two layers of film actually bond to each other? If so, how apt will the bond be to chipping?
My question is, by them doing this, will the two layers of film actually bond to each other? If so, how apt will the bond be to chipping?





RE: Amorphous Carbon Film Coating
Jim Treglio
Tribo Coating LLC
RE: Amorphous Carbon Film Coating
Thanks!
RE: Amorphous Carbon Film Coating
Jim Treglio
Tribo Coating LLC
RE: Amorphous Carbon Film Coating
Sorry to be asking so many questions, I'm just really new to this type of work and I'd like to understand as much as possible.
Thanks again!
RE: Amorphous Carbon Film Coating
A guess a more pertinent question is why are you getting the part coated? Is it for hardness or low friction?
Jim Treglio
Tribo Coating LLC
RE: Amorphous Carbon Film Coating
RE: Amorphous Carbon Film Coating
RE: Amorphous Carbon Film Coating
It should be no problem to deposit a-C:H on a-C:H:Me.
As for the chipping resistance: Try it out or ask the manufacturer about chipping tests close to your application conditions.
RE: Amorphous Carbon Film Coating
Right now, this is the process we perform on the parts before they are actually coated with the film.
Machined (no EDM at any time)
Solution annealed to 1900 degrees F
Heat treated to H900 (not vacuum furnaced)
Electropolished
Coated with TC40
Here is the latest information I have in regards to our vendors. We're going to visit the coater in a few days and I'll have more information about their process at that time...
We went to visit our electropolisher the other day and they explained their whole process to us, which seemed to all be pretty much in control. They tie up our parts with a copper wire. Next, they are electrocleaned in a HCl and water bath to remove any oxidation from the heat treating. This rinsing process is performed twice. Then they electropolish them for 30 seconds. After those 30 seconds, they take the parts and rinse them in a warm alcohol bath (not hot, but warm). After that, they dry the parts off with an air hose (compressed air). We then receive the parts from them.
I have no experience with electropolishing, so if there is something that looks odd with their process, please let me know. If no one thinks there's something wrong with what they're doing, I'll just assume that it's being done this way by everyone.
Also, does anyone here see something that could be causing the problem with flaking? Some people have suggested that we vacuum furnace heat treat the parts before they're coated. Is this a possible solution to the problem if the coater is indeed in control of their process?
Thanks a ton!
RE: Amorphous Carbon Film Coating
A usual rinsing process after is EP is: warm water rinse, flowing tapwater rinse, [unrack parts], 25 vol% nitric acid rinse, flowing rinse, flowing rinse, warm DI water rinse.
*A traditional electropolish solution is 63 wt% phosphoric acid + 15 wt% sulfuric acid + 22 wt% water (absolute wt. concentrations from titration & specific gravity).
RE: Amorphous Carbon Film Coating
Here is the confusing thing. We just had three lots of parts coated and the two that we've tested passed 100%. The thing that's even more confusing is that if the lots pass or fail, it's always 100% pass or 100% fail. There's never one part that's different from the rest.
We've been looking to the surface finish on the area that's been flaking. Our drawing calls for a 32 surface finish on the entire part, but the surface that has flaking issues is sometimes to spec and sometimes is not.
Other than the possible machining cause, does anyone see something that should be looked at more closely???
Thanks for your help!
RE: Amorphous Carbon Film Coating
When we visited the vendor, they told us that our parts are not processed on their own. They said the parts are processed when there are enough parts available for a full load, regardless of whether or not they’re our parts. Therefore, our parts are mixed in with other parts, most likely larger than ours as the part we’re having an issue with is about 1”x4”x1/4.”
After observing the bad parts next to the good parts, we came up with a question.
Could the load density be a leading factor in how well our parts are coated? Also, could the size of the parts that are coated with ours be a reason that the coating doesn’t reach all areas of our parts?
Thanks again…
RE: Amorphous Carbon Film Coating
Also, the other parts might not be as well cleaned as yours. This may affect your parts, if something is vaporized in the vacuum chamber and reaches the surface of your parts.
RE: Amorphous Carbon Film Coating
Also, with the ultrasonic bath. What should be used in that solution? Right now we're using Softsoap from a drug store. Is there something better to be using???
Thanks!
RE: Amorphous Carbon Film Coating
If all the above fail here is a top of the line cleaner.
http://www.espi-metals.com/metals/catdecontam.htm
RE: Amorphous Carbon Film Coating
ASTM B912, 'Standard Specification for Passivation of Stainless Steels Using Electropolishing,' doesn't specify polishing time. http:/
Two important things about cleanliness for your parts:
1) Prior to electropolishing, parts should pass a water-break test. A simple one: wet part with DI water and verify that it forms a continuous smooth film w/o beading.
2)After the entire EP process (including handling with white linen gloves or similar) is completed, the surface can be tested for contaminants: It is rinsed with an extractant (e.g., DI water-alcohol (spectroscopy grade) solution) which is caught in a pre-cleaned container and then analyzed for contaminants. This is done by both the bio-pharmaceutical & semiconductor industries. Also described in ASTM F1374, 'Standard Test Method for Ionic/Organic Extractables of Internal Surfaces-IC/GC/FTIR for Gas Distribution System Components,' http://www
A very useful paper, 'STAINLESS STEEL TUBING INTHE BIOTECHNOLOGY INDUSTRY,' gives information on passivation, electropolishing, surface finish, testing & standards. http://
The SS parts will need plasma cleaning to activate the passsive surface within the coating chamber, so parts loading could be problematic from the process description given.
RE: Amorphous Carbon Film Coating
Since we’ve had a chamber dedicated to our parts, we’ve gotten 90% passing parts. This is good, but we still need to find out why we have some parts that are failing.
We got some of our stripped parts back (ones that had the coating stripped with 50% benzyl peroxide). However, some of them had a little bit of the coating left over on the part. Would it be alright to go ahead with coating these parts with the leftover coating on the parts, or should we continue to remove all of the coating?
RE: Amorphous Carbon Film Coating
One other thing to note is most of the vendors have their own cleaning process which normally gave us better adhesion results.
Other variables that affect adhesion is surface finish (better finish can even give worse adhesion when it becomes too good), thermal history in the chamber, chamber gas pressure and fixturing.
RE: Amorphous Carbon Film Coating
Also areas that have relatively thin coating can indicate regions that didn't get plasma etched enough and also be a region of adhesion failure.
RE: Amorphous Carbon Film Coating
Jim Treglio
RE: Amorphous Carbon Film Coating
I had another question about the electropolishing. At times, we’ve received parts of the same lot that have come back with different finishes on the 17-4. Some come back with a matte finish, while others come back with a shiny mirror-like finish. Is there any reason that you can see this happening? Could the location in the tank affect the finish of certain parts? All parts are fixtured in the same location, so that shouldn’t be a factor…
RE: Amorphous Carbon Film Coating
But, more likely, the current density issue. Anode (part) to cathode spacing should be nearly uniform, both anode and cathode must have enough current carrying capacity (cross-section relative to surface area), plus the rectifier must be able to supply enough power to do the entire load simultaneously. If underpowered, do fewer parts at a time.
Please describe the relative geometries of shiny and matte parts vs. cathodes.
RE: Amorphous Carbon Film Coating
The parts are typically hung 3 pieces to one copper wire. Each one of the parts is about 2-3" from the closest part. All of the parts are always the same part when they are sent to be electropolished, so the part geometry is always constant.
Does this give you any more information that you didn't already know?
RE: Amorphous Carbon Film Coating
IMHO, it's better to rack the parts (e.g., with copper, brass, or titanium spring clips on a copper or titanium rod) than hang from a wire. If loose or undersize wire, amperage to the part maybe below the critical current density (which varies depending on electrolyte, e.g., minimum 50 Amp/sq. ft. for 63 wt% H3PO4-15 wt% H2SO4-22 wt% H2O).
It's also essential that parts be clean (no oil!) when electropolishing. If the racker has dirty hands or gloves... See any oil sheen on the electrolyte surface?
Surfactant in the EP solution helps if parts are less than perfectly clean. Also, helps gas bubbles exit surface of part.
RE: Amorphous Carbon Film Coating