Cupronickel or copper-nickel or "cupernickel" is an alloy of copper that contains nickel and strengthening elements, such as iron and manganese. Cupronickel is highly resistant to corrosion in seawater, because its electrode potential is adjusted to be neutral with regard to seawater. Because of this, it is used for piping, heat exchangers and condensers in seawater systems, as well as marine hardware, and sometimes for the propellers, crankshafts and hulls of premium tugboats, fishing boats and other working boats.
A more familiar common use is in silver-coloured modern circulation coins. A typical mix is 75% copper, 25% nickel, and a trace amount of manganese. In the past, true silver coins were debased with cupronickel. Despite high copper content, cupronickel is silver in colour.
Thermocouples and resistors whose resistance is stable across changes in temperature contain the 55% copper-45% nickel alloy (constantan).
Monel metal is a nickel-copper alloy, containing a minimum of 63% nickel.
Read more about Cupronickel: Other Names, History