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Silver plating of Kovar for a high temperature application

2004

Hello,

I am having some trouble properly specifying a nickel strike/silver plate process for a couple of small threaded Kovar parts. I chose silver because of the need to prevent oxidation and galling at service temperature (approx. 450C, cyclic, possibly in air, usually in vacuum). Supposedly silver plate is good to 650C but upon initial heating the silver pealed off the threads almost completely. The plater claims (after the fact, unfortunately) that I should have noted the part service temperature as this info would have flagged them to perform the plating process differently (again, no real info as to what 'differently' denotes). Nothing I have found in print suggests that silver must be processed in a certain way in order to fully utilize the oft published temperature range. Can anyone describe the problem and how silver should be properly specified for this service environment?

Thanks.

Etienne Hancock
Mechanical Engineer - Waterbury Ctr., Vermont, USA