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Platinum plating on Nickel base superalloys

I am having problems plating out platinum on nickel based alloys (Nimonic 75 and CMSX4). I am using the 5Q salt, maintaining a temperature of 92 deg C, pH 10.5 and CD ranging from 2.4 - 0.6 A/dm2. I am cleaning the alloys by initially grit blasting with chilled iron grit followed by warmacetone ⇦this on eBay or Amazon [affil links] Warning! highly Flammable! (30 °C) in an ultrasonic bath for 30 mins. I am using a pure platinum gauze for an anode.

I get some very dull matte deposits and sometimes yellow deposits (only once a shiny deposit - however there was a yellow deposit on anode).

Any suggestions appreciated!

Mark Craig
Student - Cranfield, UK
2007

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If I was plating a high nickel alloy with platinum, I surely would not blast it with iron as you will leave traces of iron in the surface.
High nickel alloy requires some aggressive preparation. too much to put here. Check out your local library or make a trip to a good college library for a book on plating. Try to find a copy of the Metal Finishing Guidebook, or a copy of the Electroplating Engineering Handbook [on AbeBooks or eBay or Amazon affil links] or other good text.
You will need to nickel strike it with a Wood's Nickel strike ( I prefer the formulation with a high HCl content and a low nickel metal content. It is slower , but it sticks well).
You do not provide data on the rest of your plating solution. No one can help you on that until you do.

James Watts
- Navarre, Florida
2007

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2007

Thanks.... I am using the Platinum 5Q plating solution as sold by Johnson Matthey at 92° C and a pH of 10.5.

I would prefer to plate without the use of Ni strikes as I would like to ultimately make various intermetallic coatings and compare these against coatings produced by other techniques.

The grit blast/ acetone ⇦this on eBay or Amazon [affil links] Warning! highly Flammable! route has been used previously in a number of papers I have read - if you could suggest an alternative method I would appreciate it.

Many thanks

Mark Craig
PhD Student
Cranfield University

Mark Craig
- Cranfield, UK

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2007

Mark
Grit blasting will change the surface morphology and the risk of iron contamination has been stated.
Acetone cleaning is typical of academic papers but is never used by platers. It is a a poor degreaser in that it evaporates rapidly and puts the grease back on the surface. Also it is highly flammable - don't heat it - I lost a perfectly good set of eyebrows when I was young!
Solvent degrease (if you must) as a first step. A good aqueous alkaline degreaser comes next. Rinse thoroughly and ensure that the water film covers the surface ie, there is no organic contamination left on the surface. This is called the water break test.
The next problem is to remove any surface oxides and produce an active surface. I do not have a specific pre-treatment for your alloy but, if you cannot nickel strike, I suspect that a fluoride etch will be needed.
Platinum plating is not easy and Q salt can degrade. Take your problem back to the supplier. If JM cannot help, try Metalor.

Geoff Smith
Hampshire, England

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First of two simultaneous responses --

Hi Mark,

Why don't you go to the Horse's Mouth and approach the (now) Hereford Company of Special Metals Wiggin who, I like to think, made the first Nimonics in the world.

Surely their lab people or chief metallurgist could help you out. OK?

The other suggestions were made by very knowledgeable people ... although I feel sorry for the guy who lost his eyebrows !

Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).
2007

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Second of two simultaneous responses --

I would use aluminum oxide for a grit blast. It will give more "teeth" for the plating to adhere to. You can give it a short soak in a caustic cleaner and it will dissolve any of the grit that might be stuck in the surface. Control your grit size and air pressure to give the surface roughness that you desire. I would try 220 first and change from there. Make sure that your air is oil free!

James Watts
- Navarre, Florida
2007

As an alternative to Woods strike and after a proper cleaning cycle you can try to activate the surfaces in forward polarity in diluted Hydrochloric acid in DI water. This solution must be very VERY clean and free of dissolved metal salts preferably reagent grade and the anodes made of graphite, again very clean and free of metal inclusions. Obviously this is not an industrial approach as chlorine gas evolves abundantly which will be irritant and must be ventilated.

Guillermo Marrufo
Monterrey, NL, Mexico
2007

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