Nickel plating is a process that deposits a thin layer of nickel onto an underlying metal. Some of the benefits of nickel plating include increased resistance to corrosion or rust, improved resistance to wear, strength, and improved ductility. Nickel plating is often seen on hardware for household use such as faucets, door hinges, and toasters. Military and aerospace use nickel plating to protect parts from corrosion.
Two different methods may be used to add nickel plating: electrolytic, also called "galvanic," and purely chemical, also called "electroless." Electrolytic plating involves passing a small electric current between the positive and negative electric poles, thereby depositing nickel on the object being plated. The chemical method relies wholly upon a chemical reaction to apply the layer of nickel.
Electrolytic nickel plating commonly uses the technique of first depositing a thin copper film on the material being plated, the substrate, then plating nickel onto the copper. The reason for this approach is that copper will adhere to other metals better than nickel. Copper first, then nickel is a quicker process with a smoother and more consistent finish than plating nickel directly onto the substrate. Either way, the surface of the substrate must be chemically clean before the process begins. Rinsing or other cleaning after is usual.
Electroless nickel plating deposits a nickel-phosphorous, nickel-boron alloy, or nickel/Teflon® coat on the substrate. Each of these produces different characteristics in the finished product. Nickel/Teflon® is a newer composite which reduces or eliminates the need for liquid lubricants. Nickel-boron produces the hardest surface.
The most common plating, nickel-phosphorous, produces a hard surface when small amounts of phosphorous are used. It also creates a bright surface and a speedy process with moderate levels. This type of plating provides very high corrosion resistance, and is suitable to use in highly acidic conditions like oil drilling or coal mining, when high levels are used.
The advantages of galvanic nickel plating over electroless plating include a more attractive appearance, better ductility, and a less expensive procedure. Galvanic plating also generates fewer environmentally unfriendly waste products. Electroless plating provides better results for complex shapes because it adheres uniformly whereas galvanic plating tends to deposit more nickel on edges. It has a higher resistance to wear than galvanic plating, and it can provide very good corrosion resistance if applied with enough thickness. Electroless plating also has possibilities, such as being paired with Teflon®, that the galvanic process lacks.