Nickel Plating Adhesion Problems & Adhesion Testing

A. Hi Jeremy, although you are nickel plating rather than chromating or anodizing the aluminum, I think step 1 in troubleshooting may remain the same: buy new coupons :-)

Step 2 is probably to insure that the coupons are going through the same zincating process as the parts.

Luck & Regards,

A. Mr. Rajgopalan, I do not know a non-destructive test for nickel adhesion, but the simple destructive test is soldering a plug or a wire to nickel for pull testing.

A. Have your supplier produce a test coupon using the same processing as the parts in question and then you can do a bend test.

A. Run a rounded steel tip over the part 10-12 times. If the adhesion is bad it may flake off or may not. The best way would be to try and lift off (exfoliate) the plating by rubbing a file on the edge of the part. nickel should grate off as a powder which is OK and not come off like a banana peel.

A. Would a transparent self adhesive / scotch tape not do a job? Try it. Stick it well on product and try to lift with another end at one stroke. If plating comes off, you need to improve on pre treatments. A destructive test on coupon can be done. Try bending a coupon.

A. Pepe:

Disculpa la pregunta pero que es ese material B4A2C y que es ese acabado F70E4A? Es acero, aluminió que? Por otra parte, la prueba del doblez con cinta (bend tape test) se realiza sobre un cupón de acero de 1mm x 25mm x 100mm el cual se recubre y se dobla a 90 degrees, posteriormente se le adhiere la cinta (es especial y la fabrica 3M). Se le da un tirón fuerte en forma perpendicular. No debe observarse ampollas ni desprendimientos. Otra prueba mas severa es rectificar el cupon con piedra abrasiva.

Saludos y feliz navidad.

----
Ed. note: This is an reply from a long time ago. We thank Guillermo greatly for his efforts to translate to Spanish to help his countrymen, but Finishing.com can no longer print inquiries and replies except in English. Sorry.

A. Use the slash test. Criss-cross the plated part with hatches cut into the surface with a sharp blade. Firmly adhere adhesive tape to the part, over the hatches and quickly pull it off again. Any poor adhesion will result in metal being attached to the tape. I do not know if there is a prescribed standard for this test, but it is very effective.

A. Additionally, I would bake the parts before doing the cross-hatch test. With extremely poor adhesion on aluminum, the plating may bubble just from the bake. Seeing if the adhesion is poor from the bake alone gives you the opportunity to see if your adhesion is "very poor" or "poor" (pass bake, fail cross-hatch).

Defelsko Pull-Off Tester

on eBay or

Amazon

(affil links)

A. Thank you for the kind words, Mustafa. I am not experienced in trying to lower the stress in Watt's nickel baths, so I may not be able to help you personally, but I think the first thing you need to do is to try to quantify the stress you are getting. Please look into "Stress Tabs" or consider getting a stress measuring instrument from Industrial Instruments Inc. or Special Testing and Development Co.

Once you have numbers, you can figure out whether the problem is so severe that it must be something obvious like excessive chloride, or whether it is the high end of normal and perhaps able to accept some tweaking like you are thinking of, or already at the low end. It is bad practice to mix a home-brew addition agent into a proprietary bath, so you should be trying your best to get help from the vendor. Good luck.

A. The problem is with the watts nickel. The high chloride results in a tensile stress, just as you say. If you reduce the amount of chloride in the bath, that will reduce the stress. Alternatively you can bromide instead of chloride and this will help a bit. The stress can also be reduced by using sodium saccharin - say about 1 g/l. Alternatively you can change from Watts nickel to nickel sulphamate. Other agents, such as napthalene trisulphonic acid (NTS) will reduce the stress, but it is a very nasty chemical to use in a plating bath because once in, it cannot be removed, except by using it up. Hence you need to be very careful about your additions! Since you are barrel plating, you are limited in the amount you can reduce the current density to reduce the stress.

A. Hi, Francisco. Tell us more about the nickel strike. To my knowledge you are limited to copper cyanide or alkaline electroless nickel after zincate. Dini's "Electrodeposition - The Materials Science of Coatings and Substrates" has a great chapter on "Adhesion".

Regards,

A. Scientists call it inter-diffusion meaning that both metallic layers tend to penetrate and mix one into the other. Thus, the definite and clear boundary or union plane which is the weak point for adhesion failures disappears.

A. Hi Poovarasu. We appended your inquiries to a thread about adhesion testing of nickel plating. The most accurate, but somewhat tedious, approach would probably be the Modified Ollard Test as illustrated in letter 18002, "Hard Chrome Plating Bond Strength and Test Methods: Modified Ollard Test". Best of luck.

Regards,

A. Re. adhesion strength of Ni plating. We (at Hoyt Co) experimented with Ni plating cast iron bearings to see if adhesion of Sn base bearing alloy could be improved by a Ni inter layer. We found bond strengths of Ni to cast iron of around 54 N/mm2 by using the Chalmers test which is destructive testing of a machined specimen.

A. Hi Jane. Easiest would probably be to whack the end of the tube with a hammer to make it either flatten or shatter (depending on how soft the tube is). Alternately, if the tube is soft, wrap it around a suitably sized mandrel. If the adhesion is excellent, the nickel plating will adhere despite the stretching or shattering.

Regards,

A. Good day Jane.

Ted has offered some good advice.
I would like to add that the adhesion of nickel on the brass threaded tubes can be compromised, as threaded brass contains lead.
Dependant on your cleaning cycle, I did deal with the lead issue, whether it be be a fluoboric acid dip/ sulfuric + fluorides (sulfuric acid alone will not remove the lead oxide produced from electrolytic alkaline cleaning).
I like to use the bend and break test, or the saw and grind test.
I place the item in a vise, and flatten the tube as Ted has suggested, or grind the tube trying to "pull" off the nickel plating.
A bake test is also useful,(650-700 °F? @ 1 hour) as it is non-destructive, however there will be discolouration of the nickel if the organics (nickel brighteners/wetter) are not removed prior to baking.
Hope this is useful.

Regards,

A. Hi Jonathan. While poor adhesion is the cause of many such problems, another potential cause is the plating being too stressed and brittle. Even with perfect adhesion, if you severely bend highly stressed and brittle plating it will crack off. You might try plating "stress tabs" and see what kind of tensile stress you are dealing with. What is the substrate ... steel? What kind of plating are you doing ... Watts bright nickel? Have you tried dull nickel or sulfamate nickel?

Regards,

A. Hi Jim. To my obviously limited knowledge I think you're in totally uncharted territory trying to use a non-destructive test of that sort. While I suppose you could get the strongest adhesive tape you can find, and decide that adhesion is good enough if the part passes, you'd need to test every one -- which seems as hard or harder than stripping and replating.

There are baking tests for nickel adhesion which should be more practical if your grinding wheels can otherwise accept the heat, and if the baking is not enough to disturb the hardness of the nickel. Hopefully someone can advise how hot and for how long, but I think it's quite iffy.

Regards,

A. Hi David. I happen to have seen a similar problem which was very easily solved, except in my case it was nickel + gold plating, and for that reason the barrel loads were very small; so I'm not sure if the cause of that problem was the same as yours ...

But what happened in my case was the barrel loads were small, the crimpable parts were quite light, and the barrel rotation relatively fast, so the parts got carried to the top of the barrel, and were taking a long time to flutter back down back into contact. Whether the actual problem was the consequent extensive make & break during nickel plating, or whether it was high tensile stress in the plating because of current density much higher than we thought because of so few parts in actual contact, I don't actually know ... because the problem was instantly and completely solved by greatly reducing the rotation speed of the barrels.

So start by considering whether the parts are properly tumbling over each other near the bottom of the barrel, or whether they're fluttering around. If that's not it, I'd suggest trying to plate at a significantly higher current density and then a significantly lower current density to see if there is an improvement. When parts are crimped it's not solely an issue of adhesion, it's also an issue of stress because if there is already very high stress, the plating can flake off no matter how well it adheres. Berl Stein's article on stress might be interesting reading for your situation.

Luck & Regards,