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