NICKEL ALLOYS electroplated for engineering applications include nickel-iron, nickel-cobalt, nickel-manganese, and zinc-nickel. Zinc-nickel plating is covered elsewhere in this Volume; see the article "Zinc Alloy Plating." Iron is a cheap metal, and solutions for plating nickel-iron alloys were developed mainly in order to reduce the cost of the metal used to form a layer of given thickness, but they were also developed for special magnetic purposes. Cobalt and manganese are used to increase the hardness and strength of nickel plating. Additionally, nickel-manganese alloys have improved resistance to sulfur embrittlement when heated. Alloy layers 20 to 30 ^m thick of nickel with about 15% Mo exhibit higher hardness and resistance to corrosion than pure nickel but at the expense of a reduction in ductility to around 1% (Ref 1). Coatings of nickel-tungsten show very high resistance to corrosion, but they are believed not to be true alloys (Ref 2) and have not been used in practice. This article will discuss the alloys nickel-iron, nickel-cobalt, and nickel-manganese that are of practical interest, plus a few paragraphs on nickel-chromium binary and ternary alloys.

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