Copper-Nickel Alloys (Cupronickel) is an alloy of copper that contains nickel and strengthening elements, such as iron and manganese.  

Sometimes called cupro-nickels, there exists a range of different copper nickel alloys that possess different properties and hence are suited to a range of different applications. Some of the better known copper nickel alloys include:  

1.Copper with 10% nickel

2.Copper with 30% nickel    

3.Copper with 25% nickel with 0.05-0.4% manganese   

4.Copper with 45% nickel (also known as constantan)      

All copper nickel alloys consist of only one phase as the copper nickel binary system exhibits complete solid solubility.   

Properties of the alloys are as follows:     

Advantages:

1.excellent resistance to seawater corrosion;

2.high inherent resistance to biofouling;

3.good fabricability.

Uses:

When it coms to copper-nickel alloys, a 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. As copper-nickel alloys's resistance corrosion, 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.  

As copper and nickel alloy with each other easily and have simple structures, the alloys are ductile and readily fabricated. Strength and hardness for each individual alloy is increased by cold working; they are not hardened by heat treatment. Joining of 90–10 (C70600) and 70-30 (C71500) is possible by both welding or brazing. They are both weldable by the majority of techniques, although autogenous (welding without weld consumables) or oxyacetylene methods are not recommended. The 70-30 rather than 90-10 weld consumables are normally preferred for both alloys and no after-welding heat treatment is required. They can also be welded directly to steel, providing a 65% nickel-copper weld consumable is used to avoid iron dilution effects. The C71640 alloy tends to be used as seamless tubing and expanded rather than welded into the tube plate. Brazing requires appropriate silver-base brazing alloys. However, great care must be taken to ensure that there are no stresses in the Cu-Ni being silver brazed, since any stress can cause intergranulary penetration of the brazing material, and severe stress cracking (see image). Thus, full annealing of any potential mechanical stress is necessary.   

Applications for Cu-Ni alloys have withstood the test of time, as they are still widely used and range from seawater system piping, condensers and heat exchangers in naval vessels, commercial shipping, multiple-stage flash desalination and power stations. They have also been used as splash zone cladding on offshore structures and protective cladding on boat hulls, as well as for solid hulls themselves.

Copper nickels are commonly specified in heat exchanger or condenser tubes in evaporators of desalination plants, process industry plants, air cooling zones of thermal power plants, high-pressure feed water heaters, and sea water piping in ships. At present, cupronickel remains the basic material for silver-plated cutlery. It is commonly used for mechanical and electrical equipment, zippers, jewelry items, medical equipment, and as material for strings for string instruments.