Metal finishing Q&As since 1989

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A hydrogen embrittlement and coated wire puzzler

 

I have been plating onto Nitinol (nickel titanium) wire that has a dielectric jacket over all but the exposed area to be plated. I have noticed a change in the flexibility of the wire and assume that hydrogen embrittlement is occurring. To start to fix the problem I have tried baking at 400 F for 1 hour and this looks like it is worse. The only thing I can think of right now is that there is a residue stuck under the plastic that is heat activatable and attacks the metal.

Is there a way to remove hydrogen that might avoid this? I am going to try a vacuum oven next.

Larry Jansen
- Portland, Oregon

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Larry, you need to do some reading. Check out 'superelasticity' and 'shape memory alloys'. Nitinol is one of these and the effects of heating and cooling on Nitinol are very much different than our intuition expects. Ted Mooney, P.E. Striving to live Aloha finishing.com - Pine Beach, New Jersey   Baking can make it worse before it starts making it better because it is simply diffusing the hydrogen at a higher rate, both out of the metal and farther into the metal. The dielectric coating is probably an out-gassing barrier. Try longer time, the vacuum won't hurt, but the partial pressure of hydrogen in your oven is already practically nil, so it won't help much to evacuate. Mike Mcguire - Pittsburgh, Pennsylvania, USA

Whoa--, just because it is stiffer after plating does not in anyway indicate hydrogen embrittlement! Now if you have had failures and highly qualified metalurgist(s) destructively evaluated it, and said it was hydrogen embrittlement, or you had some expensive outgassing work done, then OK.

James Watts
- Navarre, Florida