Metal Finishing Guide Book


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Page 308 of 843

Fig. 5. Effect of temperature on the tensile strength, yield strength, and elongation of electrodeposited nickel. Hydrogen Embrittlement Highly stressed, highstrength steels are susceptible to hydrogen embrittlement during normal plating operations. Because nickel plating is highly efficient, hydrogen damage is unlikely to occur as a result of nickel plating per se. The pretreatment of steel prior to plating, however, may require exposing the steel to acids and alkalies. During these operations, excessive amounts of hydrogen may evolve which may damage steels susceptible to hydrogen embrittlement. Steels that are susceptible to hydrogen embrittlement should be heat treated to remove hydrogen. The time required may vary from 8 to 24 hr depending on the type of steel and the amount of hydrogen to be removed. The temperature is of the order of 205ºC (400ºF), and the exact temperature may be alloy dependent. NICKEL ELECTROFORMING Nickel electroforming is electrodeposition applied to the production of metal products. It involves the production or reproduction of products by electroplating onto a mandrel that is subsequently separated from the deposit. It is an extremely useful technology that continues to grow in importance. Conventional Processes The composition, operating conditions, and mechanical properties of deposits from the electrolytes most often used for electroforming (Watts nickel and conventional sulfamate) are given in Table III. Nickel sulfamate solutions are the most popular because the deposits are low in stress, high rates of deposition are possible, and the thickness of the deposit is less affected by variations in current densities than are deposits from Watts solutions. By maintaining the solution as pure as possible and the chloride as low as possible, the internal stress of the nickel sulfamate deposits can be kept close to zero. Watts solutions are very economical. High-Speed, Low-Stress Process A concentrated nickel sulfamate solution has been recommended for electroform301

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