How to prevent electroless nickel coating from flaking after forming?
How to prevent electroless nickel coating from flaking after forming?
(OP)
We have a hollow cylindrical part made from electroless nickel plated carbon steel that gets formed at one end over another part at about a 45 degree angle. The EN plating sometimes flakes off in the formed area during this operation. The base material is 1018 steel and the plating is done per MIL-C-26074, class 1. The plating is less prone to flake when the thickness is .0005"-.001" compared to .0015"-.002", but the spec doesn't require the plating to pass the corrosion test with the thinner plating. We recently changed to a high phosphorus plating, but this didn't seem to make much of a difference with a plating thickness of .0015"-.002". Any suggestions?





RE: How to prevent electroless nickel coating from flaking after forming?
4.5.2 Adhesion test
The test specimen shall be bent 180° over a mandrel
diameter 4 times the thickness (0.4 inch minimum) of the specimen.
The EN coating should not flake after the adhesion test. I suspect that your forming procedure is more severe on the EN and the base metal than just the required adhesion test.
RE: How to prevent electroless nickel coating from flaking after forming?
RE: How to prevent electroless nickel coating from flaking after forming?
Another issue, perhaps, is that the nickel just isn't adhering properly and there may need to be some sort of intermediate layer that sticks to the nickel better, but also sticks to the substrate better.
TTFN
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RE: How to prevent electroless nickel coating from flaking after forming?
RE: How to prevent electroless nickel coating from flaking after forming?
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: How to prevent electroless nickel coating from flaking after forming?
The ENP coating ends up with a green oxide finish if not in a controlled atmosphere but which can easily be removed with a mildly abrasive pad (scotchbrite or such like).
Check the plating rate also - if it is too fast it is more likely to have adhesion problems.
Riadsala
Metallurgist in the Offshore O&G industry
RE: How to prevent electroless nickel coating from flaking after forming?
RE: How to prevent electroless nickel coating from flaking after forming?
Riadsala
Metallurgist in the Offshore O&G industry
RE: How to prevent electroless nickel coating from flaking after forming?
Have you solved this problem yet?
It is definitely an adhesion issue as suggested above. Electroless nickel should never flake off of 1018, regardless of degree of forming, merely crack, as its adhesion strength should be 50-60 ksi.
If the plater has poor pretreatment techniques or the EN bath has been heavily used (ask "What is the number of metal turn-overs? as by-products build up), two ways to improve:
1) Use a Wood's nickel (electrolytic) strike plating, and
2) Do a post-EN plating adhesion bake of 2-4 hours at 180-200 °C [ASTM B733 Class 3 adhesion bake for EN on steel).
The maximum hardness is usually achieved by 1 hour at 400 °C (depends somewhat on [P]) but is accompanied by a decrease in corrosion resistance. Don't put plated parts into a hot furnace -- best to heat up from room T. Longer times & higher temperatures result in softening -- grain growth, coarsening of the Ni3P precipitates.
For some good info on EN, go to http://www.nickelinstitute.org (free registration req'd) and download 'Properties and Applications of Electroless Nickel' (10081).
For pretreatment for proper adhesion, see
'Basic Substrate Strategies and Approaches for Electroless Nickel,' http://www.pfonline.com/articles/web0301.html