Adhesion of nickel plating onto titanium

letter 278

Plating Nickel onto Titanium

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Hello!

I am looking into the improvement of my laboratory's ability to plate Ni on to Ti because of we are having problems meeting extremely rigorous adhesion criteria.

At this time our Ti substrate is grit blasted with Al2O3 media, ultrasonically cleaned with alkaline cleaner, etched with 35% HNO3 + 2% HF, and then given a standard Woods Ni strike. After that the parts are electroplated with a few more mils of Ni using a conventional Ni sulfamate bath, and then a final layer of electrodeposited Sn is added to the parts. We are seeing loss of adhesion between the Ti and the Ni.

I spoke with a couple of vendors yesterday (Atotech and Enthone OMI), and they made the following suggestions to improve the adhesion between the Ni and the Ti:

Atotech Vendor:
1) Instead of a standard Woods nickel strike, he suggested switching to a nickel bromide strike. He said that since nickel bromide attacks Ti in aqueous solution (quoted Ti basket vendor indications and literature), then it should activate the Ti surface to a greater extent than NiCl strike.
2) Increase the duration of the Ni strike. He said for us to analyze the region of poor adhesion on the Ti part and look for a pincushion effect. If there is a pincushion effect then it is likely from areas of the Ni strike that are not thick enough. This would allow any exposed areas of the Ti to become passivated, and could be easily avoided if we just make the Ni strike thicker.

Enthone OMI:
The vendor from Enthone OMI indicated that we cannot be entirely sure that our problem is between the Ti and the Ni because of how thin a Ni strike typically is. If any passivation occurs to the Ni strike before Ni sulfamate (i.e. while the parts are waiting in a beaker of water) it could be enough to result in poor adhesion between those two layers. As a remedy to this problem he suggested that immediately prior to Ni sulfamate we perform an additional HNO3/HF etch for 10 seconds (or so) followed by a rinse step.

If anyone else has suggestions for my process of plating Ni on to Ti, please feel free to ccmail me at my return address.

Thanks,
Chris Adams

Gw Christian Adams -
Lockheed Martin

Getting adhesion onto titanium isn't easy, as you know. You might want to check Volume 5: Surface Engineering of ASMI's Metals Handbook which suggests immersion in much stronger nitric/hydrofluoric acid than you are using; followed by immersion in a hot and strong dichromate/HF mix; followed by acid copper plating.

Ted Mooney, P.E.
finishing.com
Brick, New Jersey

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I would suggest looking into Aurobond TCL Gold Strike (Sel-Rex) for the initial strike for Ti. It has always been superior to Wood's Ni strike for difficult SS plating problems. Sel Rex does recommend it for Ti.

Kirk McGlothlan

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We once plated gold onto Ti wire, we used an existing process we have for plating onto Mo wire

Which is....
Anneal the wire at 900C at 15metres/min under H2
0.5 -1.0 micron Flash in Ni Sulphamate... (There is no real need for electrolytic cleaning as this promotes oxide on the Ti)
A gold flash may also help, as when the material is re-annealed a Ni/Au alloy is formed.
Re-Anneal at 1100C at 15/M.Min to diffuse some Ni into the Ti
At this stage check for blistering, if there is still oxide on the Ti, the nickel will not diffuse..

Plate..

Hope this is of some use...

Mike Montgomery

Chris,

Following up on Enthone/OMI's comment; I think in any bonding problem (plating or other) it's important to find to identify the true plane of failure, in this case Ni strike / Ti,or possibly sulfamate Ni / woods Ni. You may save yourself some time amd money in the long run by having some elemental analys run. Most SEMs are equipped with xray analysis and xray mapping capability. If this is not available inhouse you might try a local university, or a company that offers analytical services.

This is a fairly routine kind of analysis now.

Paul D. Stransky, CEF
- Putnam, Connecticut

I have plated nickel on titanium with adhesion values up to
35,000 psi (ring shear test). The process involves grit blasting
the titanium, striking in a sulfamate bath and diffusion bonding
in a vacuum oven at 1000 C. Works every time.

R.D. Mikkola
aerospace - Oak Ridge, Tennessee

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I am picking up on a letter from Christian Adams, in which he talks of a Nickel Bromie strike bath. Has anyone the breakdown on this bath, or info. on who sells it?

Thanks,

A. Lowe

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I believe I used to analyze a nickel bromide bath. I don't remember the concentrations, but the solution looked about the consistency of lime juice, so what would that be, about 1 oz./gallon nickel metal? , I think the bromide will analyze using the usual nickel chloride titration and making the atomic weight adjustment., pH is about 2.0, I believe. Since the bath is thin, use a low current density, you are only using it for activation of the Ti, based on the above answers to the original question.

Tom Pullizzi
platronica.com
Falls Township, PA

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Correction! D. Gardner Foulke, in "Electroplaters' Process Control Handbook" [link is to product info at Amazon], 1975, Robt. Krieger Publishing, Malabar, Florida, informs me that Bromide will interfere with that chloride analysis, so I guess I used to do the EDTA titration for nickel, and calculate from there.

Tom Pullizzi
platronica.com
Falls Township, PA

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