Silver Plating is Blistering
A discussion started in 2007 but continuing through 2018(2007)
Q. We are plating Silver .002 to .004 inches thick over nickel strike. Nothing out of the ordinary. After 10,000 hours at 400F, the silver plating shows blistering. I know this is not unexpected after such a test, but my question is: What is the mechanism that causes the silver to blister? It seems that in order to form a blister the silver must have been stretched and plastically deformed by some force. What is the is the source of this force? A colleague has suggested differential thermal expansion of the silver after the plating bond is broken. Is this plausible?Kenneth W. Cornett
- North Haven, Connecticut, USA
A. Blistering is normally a result of improper cleaning or the strike. It can also result from the brightener component in the silver breaking down and volatilizing. There is an outside chance that you are baking out hydrogen from hydrogen embrittlement, but I would have thought that it would have shown up a lot sooner.
- Navarre, Florida
A. Some silver brighteners are antimony, some are selenium; both cause a stressed deposit that cannot take high heat.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
Editor's note: Mr. Probert is the author of Aluminum How-To / Aluminio El Como
A. Where does one start? Your colleague could be on to something, but there are a zillion other possibilities. If your bake cycle is indeed 10,000 hours (=400 days!), all sorts of diffusion can occur - is your substrate copper? If it is some sort of brass, bronze or such, my guess is insufficient nickel to prevent copper-silver diffusion which in the right proportion form a brittle intermetallic and upon cooling -- lead to you guessed it. What does the interface between the blister and part look like - both surfaces might give all a hint!
Milt Stevenson, Jr.
Syracuse, New York
A. What is the atmosphere? If it is air,then:
- New Jersey
A. More details (substrate, process details, exposure atmosphere) may be necessary to get a response from the silver platers. Analysis of the Ni surface under the blister would help, preferably with the blister broken open inside an SEM. Analyze the gas within a blister if possible.
- Goleta, California
Finishing.com honored Ken for his countless carefully
Q. A little more info:
- Substrate is Inconel 718, a nickel-based superalloy not normally susceptible to hydrogen embrittlement
- Plating procedure is a) clean in ultrasonic tank with mild detergent, b) rinse with deionized water, c) alkaline clean 3-5 minutes (MacDermid Process 235L, Concentration 16-18 oz./gal), d) rinse with deionized water, e) acid activator (30-40% HCl), f) nickel strike (Nickel Metal 8-9 oz/gal, HCl 10-12.5%, g) rinse with deionized water, h)silver strike (Silver Metal 0.5 - 0.7 TR. oz/gal, Free Potassium Cyanide 8-12 oz/gal), i) silver plate (Silver Metal 3.0 - 5.0. oz/gal, Free Potassium Cyanide: 8-13 oz/gal)
- The silver plating tanks have Sel-rex Silver Industrial Brightener added at 4 ml / gal (nice unit mix, huh?)
- Silver anodes are certified 99.99% pure. Silver plate purity is 99.9% min (tested monthly).
- I peeled off some of the silver around one of the blisters. The nickel layer underneath was clearly oxidized (very dark grey in color)
- I don't think out-gassing is the culprit. I just can't see where the gas would be coming from. The parts were examined every 1000 hours. No blisters were seen until the 6000 hour mark. If caused by out-gassing, wouldn't this have occurred much sooner?
- Identical seals (processed at the same time and in the same tanks) showed no blisters after 10,000 hours at 150 °C.
- Identical seals (processed at the same time and in the same tanks) but with gold strike before the silver strike show no blisters after 12,000 hours at 250 °C.
- All tests were conducted in standard atmosphere
- North Haven, CT,USA
January 18, 2012
Q. I am having a problem getting silver to not blister in a 900 degree bake. Material is ASTM A276-10 [stainless steel]. We have tried all kinds of activations. Hydrochloric acid, reverse sulfuric, actane 340, Powered direct HCl, Combined with a range of strikes. Woods nickel, sulfamate nickel, copper. Every time parts completely blister after 900 deg bake. At a loss.Ian M [last name deleted for privacy by Editor]
plater - Westfield, Massachusetts, USA
January 19, 2012
A. Hi, Ian.
I hate to respond with something as general as "read this book", Ian, but anybody who is plating onto stainless steel and hasn't yet seen Jack Dini's "Electrodeposition - The Materials Science of Coating and Substrates" may be overlooking a vital tool. Jack tested many different plating conditions, and offers actual adhesion values in his "Adhesion" chapter.
Ted Mooney, P.E.
Pine Beach, New Jersey
Silver Plated Copper Blisters when BrazedFebruary 9, 2018
Q. Hi everyone!
We have a brazing process of terminals. They are made out of copper (substrate) and have a silver plating, which is made by a 3rd party. The silver plating has to conform to ASTM B700 [link by ed. to spec at TechStreet].
These pieces are brazed to an electrical motor, but we are having two specific problems:
1) Little blisters (bubbles) after brazing.
2) After brazing, the silver plating comes off in some other pieces.
Our client is rejecting all the pieces with these problems and it's causing serious problems for us.
Do you have any ideas on how to fix this?
- El Paso, Texas
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