Nickel plating on Inconel Q&A

A. Sean, Inconel 718 is very difficult to have a good activated surface on because Inconel will build up a deactivated surface. Try to use only cathodic cleaning solution as the first step for 2 minutes. Activate cathodically in HF-H2SO4 solution for 1 minutes count, than you can see gassing from the part. Activate with no current in HNO3 solution for 10-15 sec. Use a Wood's nickel strike solution for 5,0 A/ dm2 in 5 minutes. Go to the hard nickel plating solution requirement time. If you get some smut on the surface, use pumice ⇦ this on eBay or Amazon [affil links] to get a clean surface between the pretreatment steps. Regard, Anders Sundman 4th Generation Surface Engineering Consultant - Arvika, Sweden A. Inconel is a very high nickel alloy, so it is not easy to plate. But you left out two important steps: How are you cleaning and how are you etching? The strike is irrelevant unless those two are adequate. A high acid Wood's Nickel Strike would be the preferred strike by nearly all platers. James Watts - Navarre, Florida A. Try a high chloride one such as Wood's nickel. Trevor Crichton R&D practical scientist Chesham, Bucks, UK

A. We used to do hard chrome direct on Inconel 718 after activation in H2SO4/HF 30-50 A/sq dm, and the adhesion used to be very good .

Good luck,

A. Inconel, as well as any high nickel alloy has to be struck with a highly acidic Wood's bath. Problems come when shapes are complex, since due to its high acidity, the throwing power of this bath is limited. EN can be plated on top of the Wood's without too much a problem, but to successfully gold plate on top of EN, an acid gold chemistry has to be used and transfer times kept at a minimum. Depending on your gold chemistry, a brief compatible organic acid rinse in between might help. About your other questions, current capacity of the gold plate is related to its cross-section. If too thin, current will find its path thru the substrate, lowering the overall conductivity. If dollars and volume allow it, options worth investigating would include PVD, CVD, sputtering, etc.

A. Inconel is not easy to plate as you are finding out. I have seen three procedures work after they were tweaked:
1. sulfuric-hydrofluoric mixture with a short low voltage anodic etch. Tricky point between activation and smutting.
Next was a low current-high current sulfuric acid. This was long and generated lots of fumes, but worked.
Last was a dip in nitric hydrofluoric acid.

I do not remember the exact specifics of the three approaches. You may be able to find a similar process in one of the recommended books. I would see if INCO had any suggestions. I would also check with the international nickel institute.

A. Inconel is not difficult to activate and then plate on. I have described a method here at the forum before. Jim is right there recommending hydrofluoric acid. It's necessary to see the gassing on the part when activating in hydrofluoric acid step; it could take 30 sec to 2 minutes or more without gassing and no adhesion on Inconel material.

Regards,

Hydrofluoric acid burns

Never use HF anywhere unless trained!
If you do, you MUST have the antidote gel on hand for instant use!

Calcium Gluconate
for HF acid burns

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A. Hi,

Please remember that hydrofluoric acid is only for those trained in its use, and don't even think about getting any until you have calcium gluconate gel instantly available. Platers who are inured to cyanide and chromic acid still justifiably fear HF.

Luck & Regards,


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

A. Hi, Joe.

Electrocleaning: When the work is cathodic, the scrubbing bubbles are hydrogen; when it is anodic, the scrubbing bubbles are oxygen. There is twice as much hydrogen produced as oxygen, so the cathodic cleaning action is better, but it raises the possibility of hydrogen embrittlement and the deposition of metallic smuts on the work. So cathodic followed by anodic may be best.

Electroacid: The important rule here is that you can only properly plate on an activated surface, so you do not want to end the acid cycle on a phase where the part may be passive. I think that means the work should be cathodic.

However, don't forget that electroplating is an incredibly complicated process if you try to scientifically take every little detail into account. So there is a lot of empirical knowledge involved in the process. You may never resolve the science of how many seconds of this and how many seconds of that; you may have to just go with what works, and just hold those parameters.

Regards,

A. You can get some guidance from books on plating that include prep steps.
I think that you have a poor engineering setup with Inconel being considerably more difficult to activate than the steel.
You run the risk of over activating the steel or under activating the Inconel.
I like ending on cathodic as the tank retains a charge after the current is shut down and actually reverses and the part become anodic for a second or two. The use of current requires that you have a much less contaminated tank than a simple no current or it will deposit trash during the cathodic cycle. I would experiment with a scrap part to see what might work best for you.

A. Elena,
Are you striking Inconel using Wood's Nickel - reverse and forward?

A. ELENA,

Inconel is a very high nickel content typically 13.5% and 6% Chromium.

Typical sequence for plating on Inconel :- Soak cleaning , Acid Dipping , Etching ( 20 to 30 Sec ) , Wood's Nickel Strike cathodic ( 2 to 3 minutes ) , Plating.

Regards,

A. I've never found a need to etch Inconel... My process was as follows:

1.) Soak clean
2.) Electro-clean
3.) 50% HCl for 1-2 minutes
4.) Wood's nickel strike, 3-5 minutes
5.) Plate