Properties and Classifications of Copper-Nickel Alloys (Cupronickel)

By Reginald DaveySep 27 2012

Updated by Reginald Davey 08/09/22

Possessing good properties, workability, and a wide field of commercial applications, copper-nickel (Cu-Ni) alloys are commercially important for a number of industries.

Image Credit: Vladimir Khodataev/Shutterstock.com

Introduction

Cu-Ni alloys exist as a single-phase structure throughout the entire composition range, which includes many standard alloys with minimal additions of other elements for special applications. Cu-Ni alloys were initially used for marine condenser tubes. Cu-Ni alloys containing 10 to 30% nickel with iron and manganese additions (C70600 and C71500) are commonly used for marine applications in addition to coinage and wire mesh.

Alloying Additions

Manganese combined with commercial alloys acts as de-sulfurizer and de-oxidant. It boosts resistance to corrosion in seawater.

Iron (about 2%) is added to the alloys used for marine applications. It enhances the strength of the alloy and offers resistance to impingement corrosion occurring from flowing seawater. These alloys are used for marine supplies which include condensers, tubes and other applications that come in contact with seawater. The term “copper-nickel (Cu-Ni)” refers to alloys having copper-nickel-iron.

Chromium can also be added to increase the strength of the alloy. Chromium is used in a 30% nickel casting alloy.

Niobium provides a hardening effect when added to cast versions of 10% and 30% nickel alloys. It increases the weldability of cast alloys.

Silicon enhances the casting characteristics of the Cu-Ni alloys and is combined either with chromium or niobium.

Tin provides enhanced resistance to atmospheric tarnishing. The C72500 alloy has 2% tin and 9% nickel.

Properties

Cu-Ni alloys possess several beneficial properties. They possess superior mechanical properties over a wide range of temperatures. Alloys have special properties such as low-temperature coefficients and high electrical resistivity. Additionally, their enhanced wear and corrosion resistance is key to their commercial applications, and they can resist corrosion fatigue and stress cracking.

When more than 15% nickel is added during manufacturing and processing, an attractive light color is produced, enhancing the aesthetic appeal of Cu-Ni alloys. Manufacturing methods such as hot and cold working and casting produce good processing characteristics for semi-fabrications and finished parts.

Classification

¹Cu + Sum of named elements, 99.5% min.
²Ni value includes Co.
³When product or casting is intended for subsequent welding applications, and so specified by the purchaser, the Nb content shall be .40% max.
⁴The following additional maximum impurity limits shall apply: .10% Al, .001% B, .001% Bi, .005% P, .0025% S, .02% Sb, .01%Ti.

Manufacturing and Processing Methods for Cu-Ni Alloys

Cu-Ni alloys are manufactured and processed using multiple methods. These include melting, casting, hot and cold working, heat treatments, various machining techniques, joining, and welding methods, including arc welding and TIG.

Products can be mechanically fastened with screws and rivets, soldering, and brazing, to mention a few techniques. Surface treatments can be employed to further improve the properties and durability of alloying materials. Both electrochemical and mechanical polishing can be used effectively.

Commercial Applications of Cu Ni Alloys

Cu-Ni alloys were initially used for marine condenser tubes. Cu-Ni alloys containing 10% to 30% nickel with iron and manganese additions (C70600 and C71500) are commonly used for marine applications in addition to coinage and wire mesh.

Since their development, many different applications have been researched for Cu-Ni alloys, leading to their widespread use in several industries today. Specific applications of alloys depend on their proportion of Cu, Ni, and other additions.

Copper-nickel alloys are widely used in the desalination industry in MSF plant components such as tubing for heat recovery, heat rejection, and brine heaters. Additionally, they are used in tube plates, linings for flash chambers and water boxes, and piping for various purposes.

In the offshore oil and gas industries, Cu-Ni alloys have been applied in seawater cooling and fire control systems. Their chloride corrosion and stress cracking resistance properties are widely exploited to improve the durability of these key systems. These alloys have also been commercially applied as platform leg splash zone sheathing.

The energy industry has also increasingly employed these alloys in nuclear and fossil fuel power plants for components that deal with heat transfer processes. Steam generators, condensers, tanks, coolers, valves, fittings, and pipes have all benefitted from the use of these materials.

The shipbuilding industry has also exploited the properties of Cu-Ni alloys, providing materials for critical applications such as compressed air systems, onboard desalination plants, fire systems, and hydraulic lines. Furthermore, copper-nickel alloys have found recent novel applications in plates and sheathing for hulls.

More from AZoM: A Guide to Copper Alloys and Copper Nickel Alloys

Further Reading and More Information

Nickel Institute (2022) Applications of copper-nickel alloys [online] nickelinstitute.org. Available at:

https://nickelinstitute.org/en/about-nickel-and-its-applications/copper-nickel-alloys/applications-of-copper-nickel-alloys

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