Nickel is added to copper to greatly improve its strength and corrosion resistance, and to create a new cupronickel alloy.
Nickel is completely soluble in copper, which allows a wide range of alloy compositions: from predominantly nickel with additions of copper, such as Alloy K500 (Monel® K500, 2.4375), through to predominantly copper with additions of nickel, such as Hiduron® 130 (DTD 900/4805, 2.1504).
Strengthening copper nickels
The main strengthening mechanism for combinations of nickel and copper is solid solution strengthening. Although the two metals are completely soluble in each other, the difference in size between their atomic shells creates localised stresses in the crystalline structure.
These stresses restrict the movement of dislocations when the alloy is loaded, which increases the yield strength. Other elements can be added - iron, chromium, molybdenum - to create additional strengthening mechanisms.
Both alloys contain small additions of iron and manganese, chosen to give the best combination of resistance to flowing seawater and overall corrosion.
Uses of cupronickel alloys
Copper-nickel alloys are used frequently in marine applications - seawater piping, desalination plants and power plant cooling systems - because of their excellent resistance to seawater corrosion, their low susceptibility to the attachment of marine organisms, and their ease of fabrication.