Metal finishing Q&As since 1989

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Heat treating electroless nickel overplated with gold

Hello, need to know if anyone has experience with heat treating electroless nickel after its been overplated with Gold. In our experience, there is not a big improvement in the hardness of the nickel until you reach 600°F. However, at this temperature the gold begins to discolor. The question is, can the nickel be heat treated before the gold is applied, and what problems might we encounter (Adhesion, difficulty activating the Ni, surface finish, etc...). Or perhaps there is an amount or type of gold that can be used that will not discolor after 1 1/2hr @ 600°F.

Many thanks for your help.

Scott Chabineau
electrical contacts - California
2005

If you follow the proper steps to clean and activate the heat treated EN surface you'll have no problem. It would be better to gold plate after. It will avoid your discoloration problem and will save gold from parts that will not pass QC after the heat treatment. Certainly a high purity gold will not discolor.

Guillermo Marrufo
Monterrey, NL, Mexico
2005

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Hello,

It would be better to heat treat the Ni before applying the gold. The best way is using a forming gas. Hydrogen & Nitrogen. If you use straight N2 the chances are the Ni can passivate and that will create a headache when reactivating the Ni for gold deposition.

Leonard Jackson
- Fuzhou, China
2005

We are using a type II gold, and it our belief that the Cobalt may be what is discoloring. Our local plater has taken issue with trying to stop the plating process to wait for the heat treat cycle and is claiming that we will experience poor adhesion due to the inability to reactivate the Ni. There is at least one thread on this discussion board that talks about the high phosphor content giving problems for reactivation. Anyone actually doing something like this -rless nickel plate, heat treat the Ni to increase hardness, then plate with gold (or other overplating)?

Scott Chabineau
- California
2005

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Hardening EN is a time-temperature combination. Check with the EN vendor for the tradeoffs to get the required hardness at lower temperatures. You might consider using a low Phos EN which would not require a hardening cycle, (possibly a hydrogen de embrittlement bake at 300F)
Any nickel that is baked is difficult to reactivate consistently! I would look at other alternatives before considering a plate harden plate cycle, if for no other reason than it will very probably cost at least twice as much as a plate plate harden cycle.

James Watts
- Navarre, Florida
2005