Difference between Nickel plating and Electroless Nickel plating

A. Hi John. 8 µm may seem like a lot, but on a rough and intricate surface, and followed by a nickel strike (which can dissolve some of the nickel), it may not be enough. Aluminum or zinc may be exposed. I would suggest, if practical, applying more electroless nickel to the problematic parts and seeing what happens.

Regards,

A. This has been my experience too, my best advise is to treat the aluminum with Zincate, copper plated with an alkaline copper solution, then bright copper plating following by electrolytic nickel plating.

A. Electroless nickel is far superior to electrolytic nickel for corrosion resistance. That is because it is an amorphous glass-like nickel phosphorous alloy and because the thickness distribution is far superior so there will be no thin spots. Hard chrome is not really corrosion resistant since the cracks extend through to the substrate.

A. Electrolytic nickel is deposited using DC current, while Electroless Ni is an autocatalytic deposition. Electroless Ni produces plating of uniform thickness all over the part, while electrolytic Ni plates a thicker deposit in high current density areas. Electrolytic nickel is more ductile than electroless, which tends to be brittle and glasslike. Typical electroless Ni baths use hypophosphite reducing agents and deposit phosphorus along with the Ni. Mid-Phosphorus (5-8%P) deposits are bright, hard, and magnetic as deposited. High phosphorus (9-15%) deposits are nonmagnetic as deposited, semi-bright, and slightly softer than mid-phos. High-phos Ni has greater corrosion resistance than lower phos deposits. All electroless Ni deposits can be altered by heat treatment at temperatures as low as 800 °F. Electrolytic deposits are Ni-Sulfur alloys if a brightener is used. The sulfur in the deposit reduces corrosion resistance.

A. Hi Glen:

You already got two professional answers, but adding to Ted and Mike, here are some other physical properties that you asked for. Chromium is harder (900-1100 HV), has a lower thermal expansion (around 8/1000000) and has a higher melting point (1875-1920 °C) than any nickel, either electro or electroless. Most of the time it is stressed and cracked, so it is not an impervious barrier to isolate substrates chemically, but it will resist nitric acid and other strong oxidants better than either electro or electroless nickels.

A. There is one thing that I would like to add on top of the comprehensive explanations that you already received, the low phosphorous EN deposit is almost as hard as hard chromium. That is why some platers use it as a substitute to hard chrome.

A. I just want to add one important thing that should be taken in consideration now with RoHS and WEEE regulations : most of the formulations of these electroless Nickel bath use Lead and Chromium as stabilizer and brightener. And these 2 elements co-deposit with the Ni alloy.
Some substitutions are coming on the market but are not yet common.

Ed. note: Franck's posting is a few years old and most suppliers now offer electroless nickel free of lead or cadmium stabilizers.

A. Hi, Dilip. Electroless nickel usually takes significantly longer. Plating times of 1 to 2 hours or more are fairly common, while a half hour is a long time for electrolytic nickel plating. But please don't read too much into that answer, because 'productivity' is almost never any consideration at all in choosing electroless vs. electrolytic.

Regards,

A. Hi, Mihir.

"Electrodeposited" equals electrolytic, so QQ-N-290A describes electrolytic nickel plating; but it is cancelled, so please obtain AMSQQN290.

Many suppliers have reformulated their electroless nickel processes to be free of cadmium and lead for RoHS compliance, but you should check. RoHS compliance may be required for your parts, and is advisable in any case, but is not a driver in deciding whether to use electrodeposited vs. electroless nickel.

Regards,

A. Hi Phil. Sulphamate nickel plating needs no sulfur-based brighteners so it has less heat sensitivity than other electrolytic nickel plating. Electrolytic nickel is probably easier to activate for soldering than most electroless nickels, but Nickel-Boron electroless nickel plating can be soldered with RMA (rosin mildly activated fluxes).

Plating on aluminum involves an "immersion plating" of zinc from a zincate bath; this is usually the weak link in adhesion. We have dozens of threads on the subject if you put "plating on aluminum" into the search engine.

Regards,

A. Not many affordable platings will stand up to that environment very long.

For electro nickel, thickness is very important; the more the better. For Electroless Nickel a high phosphorous will work better than a middle one. Boron EN will frequently do better yet. Here again, thickness is critical. With a problem, I would not use any less than 0.0015 inches (1.5 mils).

Consider putting a high phosphorous EN over a good base coat of electro nickel for even better results.

It will probably be cheaper to go to the part made out of 316 stainless or an even more exotic stainless.

A. Hi Divahar,

Dependent on the technology used, electroless nickel coatings will contain either phosphorus or boron, electrolytic nickel coatings tend to contain small amounts of sulfur. A suitably sensitive X-Ray Fluorescence (XRF) will be able to tell the difference by detecting the non-metallic component. Also Scanning Electron Microscope (SEM) with an EDX attachment would do the same job.

A. Hi Dave. When we in the plating industry say that electroless nickel is catalytic, we mean that the nickel plating catalyzes the reducing agent for continued deposition of more nickel from the plating solution; we are not talking about combustion. I know nothing about combustion engineering, but I have no reason to suspect that electroless nickel plating would catalyze more complete combustion.

Regards,

A. Hi Derek. Electrolytic nickel plating could possibly cause hydrogen embrittlement of high strength steel. And if a heavy layer were plated on a very thin object, the tensile stress of nickel plating could possibly compressively stress the object.

Nickel plating is done by immersion in an aqueous based bath at 140 °F, and the part could be slightly warmer, and might approach the boiling point of water earlier in the pretreatment process.

Nickel plating of reasonable thickness, so it is free of porosity and pitting, should stand up to a mild caustic wash down.

It would probably be better to describe your intended application, because that way readers might be able to warn you about potential issues rather than you having to try to imagine them. Another problem with abstract questions is that you may be concerned about the overall process whereas readers might respond in terms of just the one nickel plating step per se rather than the usual prep steps; another potential problem is that different substrates may involve different issues. Good luck.

Regards,

A. Hi Vimal. Electroless nickel generally offers significantly greater corrosion resistance at significantly greater cost. There are many responses on this thread which attempt to answer your question in terms of corrosion resistance, consistency of thickness, hardness, magnetic effects, temperature resistance, speed of deposition, etc. If you give us the specific application & situation, I think people can answer you very directly about which type of nickel plating would be best for that situation and exactly why.

But there are many different types of electroless nickel plating, many different types of electrolytic nickel plating, and idiosyncrasies everywhere -- so while a two-paragraph internet response might suggest the best finish for a highly specific case, it is unlikely to educate someone enough for them to be able to make the choice in a more general case. Metal finishing consultants usually acquire many decades of experience before they presume to predict the applicability and service life of a finish; the previously linked books by Mallory & Hajdu, and by Dennis & Such should be a good intro though. Good luck!

Regards,

A. Hi Krishna,
Where is your failure occurring? You state the reject rate is "huge". Is it due to the antique finish not being what you want once the black Ni is polished back? What would the bright electroless Ni be fixing? It seems, based on your post, you aren't satisfied with the imitation patina you end up with. If it isn't inconsistencies in the antiquing that is causing the rejects then what is?

A. Hi Dallas, electrolytic nickel is better. For details please see Sjamp van Esch's excellent response on topic 18940. Good luck.

Regards,

A. Of course zinc with a clear chromate will not withstand repeated exposure to bleach.

I'd expect electroless nickel to do very much better, but that will depend to some extent on the surface preparation and EN thickness. In this aggressive environment, I'd suggest at least .001" thick, maybe more.

However if your standard is hundreds or thousands of exposures, then you're going to have to change material.

If plastic will work, then there are multiple choices - PVC, polypro, teflon, etc. There are metal alloys too.

A. Hi Michael. The reason it's performing worse than zinc is that zinc is anodic to steel and preferentially corrodes, whereas nickel is cathodic to steel and -- once breached through a pinhole or porosity -- will accelerate the rusting.

As Jeff says, as a first step it must be thick enough to be completely free of pinholes & porosity.

And thanks for reminding our readers, through example, that salt fog testing should not be used for trying to compare the corrosion resistance of one finish to another :-)

Regards,

A. Hi again. I personally think that if EN is affordable and practical it is the right solution. When you are studying grain structure, maybe see if you can confirm what I have heard for many years, that smoothness of the substrate is key to corrosion resistance of electroless nickel. I assume that it is true and that it is because a thickness which is sufficient for a pore-free finish on a very smooth surface may still have dislocations and consequent porosity on a rougher surface.

Regards,

A. Hi Manikanda. Electroless nickel is an exceptionally corrosion resistant finish for many reasons including full coverage, even thickness of deposit, and glassy finish. I don't think you can do better. But I'm not quite clear whether you are heat treating the steel or the electroless nickel coating -- my understanding is that you can obtain that hardness without heat treating the nickel, and you'll get the best corrosion resistance by not heat-treating and by using the highest phosphorous which will deliver enough hardness. My understanding is that the smoother the finish, the better chance you have of reaching 500 hours salt spray resistance. Good luck!

We'd appreciate feedback regarding what you ultimately decided to do and what you learn! This is a public forum where we all learn by trying to help each other, and finding out whether the suggestions actually work is crucial to making it better. Thanks again.

Regards,

A. Dear Manikanta,

The replacement of steel instead of SS on the drum component won't work, there is little chance you will get to 500 hours with only EN, you will wind up giving rust stains free of cost on the clothes.

A. Hi cousin. In response to your question almost 2 years ago, I suggested trying electroless nickel, whereas Khozem expressed the opinion that only stainless steel will hold up on the wet components within a washing machine.

I think what is most absent at this point is feedback on what you've actually tried and what you're actually learning from it.
There's an expression courtesy of the bridge players of the world: "a peek is worth a thousand finesses" :-)

Luck & Regards,

A. Hi again, Manikandaprabu. Electroless nickel can hold up to salt spray testing for over 1000 hours but it does depend upon good, smooth, surface preparation and sufficient thickness (which may not be practical for this component).

If you remain unreceptive to Khozem's answer, then here's a final one for you: hot dip galvanizing followed by anodization of the zinc coating. Decades ago Fred Perlstein found this finish remarkable and, to my understanding, it was at one time used on some washing machine components :-)

References:
https://www.pfonline.com/articles/zinc-anodizing
https://www.finishing.com/125/88.shtml
https://www.finishing.com/136/06.shtml

Luck & Regards,

Thanks for the suggestion, Mr.Ted; will try the coating and let you know.