Question: We receive parts that specify a “low stress” nickel deposit. Are there numerical ranges for high- and low- stress nickel deposits? D. M.
Answer: I am not aware of any standard that specifies numeric values for high and low stress deposits. Perhaps one of our readers can enlighten us on this. That said, let's talk about stress in nickel deposits. Residual stress in nickel deposits is affected by the plating bath composition. The table below shows some stress values.
Residual Stress (psi)
Typically, sulfamate nickel is called for when a low-stress deposit is specified. The conventional Watts nickel bath, which contains sulfate and chloride, gives a deposit with a high-residual stress. Adding stress reducing agents to the plating bath can reduce this stress. In some cases, this is satisfactory but if an additive-free deposit is required, you will have to think in terms of the sulfamate plating bath.
Other factors will influence the residual stress of the deposit like temperature of the plating bath and the actual substrate itself.
A much more detailed discussion of stress and plated deposits can be found in the book, Electrodeposition – The Materials Science of Coatings and Substrates by Jack Dini. The book is available from Metal Finishing Publications, (212) 633-3199.
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