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ResourcesMaterialsCopper Nickel Alloys (CuNi): Definition, Applications, Advantages, and Disadvantages
Copper-nickel alloy coins. Image Credit: Shutterstock.com/Pavlov Roman

Copper Nickel Alloys (CuNi): Definition, Applications, Advantages, and Disadvantages

Xomety X
By Team Xometry
July 13, 2023
 10 min read
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Copper nickel alloys (CuNi) are used extensively in various industries and applications. Composed primarily of copper and nickel, these alloys possess unique properties that make them highly valued and widely used. 

This article aims to provide a comprehensive overview of copper-nickel alloys, exploring their definition, diverse applications, and the benefits they offer. Additionally, it will delve into the potential drawbacks associated with their use. 

What Is a Copper Nickel Alloy (CuNi)?

Copper nickel alloys, also known as CuNi or cupronickel alloys, are a group of alloys consisting primarily of copper and nickel, with small amounts of other elements added to enhance such properties as: strength, corrosion resistance, hardenability, weldability, and castability. The most common types of CuNi alloys are the 90/10 and 70/30 alloys. The 90/10 alloy contains 90% copper and 10% nickel, while the 70/30 alloy contains 70% copper and 30% nickel. There are also high-strength NiCu alloys that are mixed with other components, such as Cu-Ni-Al and Cu-Ni-Sn. For more information, see our guide on the Uses of Metalloids.

What Is the Importance of Copper Nickel (CuNi) Alloys?

Copper-nickel alloys are significant because of their unique combination of properties. These properties include: exceptional corrosion resistance, high thermal stability, excellent electrical conductivity, good mechanical strength, compatibility with other materials, antibacterial properties, and long-term durability, enabling their widespread use across diverse industries and applications. For example, CuNi alloys offer high thermal stability, allowing them to maintain their mechanical properties even at elevated temperatures. This makes them well-suited for applications involving heat exchangers, power generation equipment, and other high-temperature environments. CuNi’s electrical conductivity makes it an important material in electrical and electronic applications such as wiring, connectors, and terminals. 

When Did Copper Nickel Alloys Start Being Used?

Cupronickel has a long history dating back over a thousand years. Its earliest known use can be traced to China in around 300 BCE. Chinese records detail the process of creating "white copper" by heating and mixing copper, nickel, and saltpeter.

The use of cupronickel extended to the production of Greek coins. In later years, cupronickel underwent a "rediscovery" in Europe through alchemical experiments. During the period following the Civil War in the United States, cupronickel was employed by the U.S. Mint to stamp three-cent and five-cent pieces. As silver grew scarce during the war, cupronickel served as an alternative. Finally, in recent decades, cupronickel has been used as cladding or coating for American 50-cent pieces, quarters, and dimes.

What Are the Advantages of Copper Nickel Alloys?

Copper-nickel alloys offer several advantages that make them valuable in numerous applications. Some key benefits are listed below:

  1. Possess exceptional resistance to corrosion, particularly in marine and seawater environments.
  2. Copper-nickel alloys have high thermal stability, enabling them to maintain their mechanical properties and resist degradation at elevated temperatures. They can withstand thermal cycling and exhibit good resistance to oxidation.
  3. Can be tailored to meet specific requirements by adjusting the composition and proportions of copper, nickel, and other alloying elements.
  4. Can be easily fabricated and joined using common techniques like welding, brazing, and soldering.
  5. Exhibit resistance to biofouling, the accumulation of organisms on submerged surfaces, which is advantageous in marine environments.
  6. The corrosion resistance, strength, ductility, and durability in a wide range of environments of CuNi alloys contribute to their long service life and low maintenance requirements.
  7. Are known for their recyclability, making them environmentally friendly options.

What Are the Disadvantages of Copper Nickel Alloys?

Like any material, copper-nickel alloys also have certain disadvantages, such as:

  1. Copper nickel alloys can be more expensive than other common alloys due to the higher cost of copper. Nickel price fluctuations can impact the overall cost of copper-nickel materials. 
  2. CuNi alloys are generally considered less machinable than some other common alloys, such as stainless steel or aluminum alloys. The presence of copper in these alloys can cause higher tool wear and reduced cutting speeds. Machining homogeneous Cu-Ni alloys prove challenging due to their high toughness, resulting in poor machinability, particularly in their soft state. These alloys tend to produce long, pliable chips, leading to frequent issues with chip removal and adversely affecting the achievable surface quality.

How Are Copper-Nickel Alloys Processed?

Copper-nickel alloys undergo various specific processing techniques depending on the intended application and the desired final product. Some common methods used are listed below:

  1. Copper and nickel are melted in appropriate proportions. The metals are melted together in a furnace or other suitable equipment, ensuring proper mixing and homogenization. Other alloying elements or trace elements may also be added to enhance specific properties or meet particular requirements.
  2. After the alloying process, the molten copper-nickel alloy is cast into desired shapes and sizes. Casting methods include sand casting, investment casting, and continuous casting.
  3. Copper-nickel alloys can be hot-worked to shape them into desired forms. Hot working methods include hot rolling, hot extrusion, and hot forging.
  4. Copper-nickel alloys can also be cold-worked at room temperature to enhance their mechanical properties and achieve specific shapes. Cold working methods include cold rolling, cold drawing, and cold forming. 
  5. Heat treatment is often performed on copper-nickel alloys to optimize their properties. Common heat treatment methods include annealing, tempering, and solution treatment. 
  6. After the primary processing steps, copper-nickel alloys may undergo machining operations such as cutting, drilling, milling, and turning to achieve specific dimensions and surface finishes. Finishing operations like polishing, grinding, and coating may also be performed to enhance the appearance and protect the surface of the alloy.

What Are Different Applications of Copper Nickel (CuNi) Alloys?

Listed below are some of the common applications of CuNi alloys:

1. Pipe Nipples

Copper-nickel alloys are commonly used in pipe nipples, especially in industries where corrosion resistance is crucial. They are often used in piping systems that transport corrosive fluids, such as seawater or brine. Copper-nickel pipe nipples offer high resistance to corrosion and biofouling, making them suitable for marine environments and other harsh conditions.

2. Cooling Loops

Copper-nickel alloys are utilized in cooling loops, particularly in industries such as power generation, chemical processing, and oil refining. These alloys exhibit excellent resistance to corrosion and biofouling, making them ideal for use in cooling systems that circulate seawater or brackish water. They help maintain the efficiency and longevity of cooling equipment while reducing the risk of corrosion-related failures.

3. Marine Hardware

Copper-nickel alloys find extensive use in marine hardware due to their resistance to corrosion in seawater. They are employed in various marine applications, including shipbuilding, offshore structures, and underwater equipment. Examples of marine hardware made from copper-nickel alloys include: propellers, seawater valves, fittings, pumps, and heat exchangers.

4. Desalination

Copper-nickel alloys are well-suited for desalination plants, where they are used in the construction of evaporators, condensers, and heat exchangers. Desalination involves the removal of salt and other impurities from seawater to obtain fresh water. Copper-nickel alloys provide excellent resistance to seawater corrosion and can withstand the high salinity and aggressive conditions encountered in desalination processes.

5. Seawater Piping Systems

Copper-nickel alloys are widely employed in seawater piping systems, especially for transporting corrosive seawater or brackish water. They are used in a range of applications, including: seawater intake systems, cooling water systems, and fire protection systems. Copper-nickel pipes and fittings offer high resistance to corrosion, erosion, and biofouling, ensuring the durability and reliability of the piping infrastructure.

What Is the Strength Range of Copper-Nickel Alloys?

The strength of copper-nickel alloys can be influenced by cold work and alloy composition. Cold work results in the generation and pinning of dislocations, increasing, especially, the yield strength of the material at temperatures below the annealing and recrystallization points. Alloy composition offers several avenues of strengthening for copper-nickel alloys: simple solid solution strengthening, spinodal decomposition strengthening, and precipitation (age) hardening accomplished through heat treatments.

What Is the Electrical Resistivity Range of Copper-Nickel Alloys?

The electrical resistivity of different CuNi alloys is given in Table 1 below:

Table 1: Electrical Resistivity of CuNi Alloys
Alloy Identification SymbolElectrical resistivity in Ω·mm2/m (20 °C)Electrical resistivity in Ω·mm2/m (100 °C)Electrical resistivity in Ω·mm2/m (200 °C)Electrical resistivity in Ω·mm2/m (300 °C)Electrical resistivity in Ω·mm2/m (400 °C)Electrical resistivity in Ω·mm2/m (500 °C)
Alloy Identification Symbol
CuNi2
Electrical resistivity in Ω·mm2/m (20 °C)
0.05
Electrical resistivity in Ω·mm2/m (100 °C)
0.057
Electrical resistivity in Ω·mm2/m (200 °C)
0.064
Electrical resistivity in Ω·mm2/m (300 °C)
-
Electrical resistivity in Ω·mm2/m (400 °C)
-
Electrical resistivity in Ω·mm2/m (500 °C)
-
Alloy Identification Symbol
CuNi6
Electrical resistivity in Ω·mm2/m (20 °C)
0.1
Electrical resistivity in Ω·mm2/m (100 °C)
0.107
Electrical resistivity in Ω·mm2/m (200 °C)
0.114
Electrical resistivity in Ω·mm2/m (300 °C)
0.123
Electrical resistivity in Ω·mm2/m (400 °C)
-
Electrical resistivity in Ω·mm2/m (500 °C)
-
Alloy Identification Symbol
CuNi10
Electrical resistivity in Ω·mm2/m (20 °C)
0.15
Electrical resistivity in Ω·mm2/m (100 °C)
0.156
Electrical resistivity in Ω·mm2/m (200 °C)
0.162
Electrical resistivity in Ω·mm2/m (300 °C)
0.169
Electrical resistivity in Ω·mm2/m (400 °C)
0.175
Electrical resistivity in Ω·mm2/m (500 °C)
-
Alloy Identification Symbol
CuNi23-Mn
Electrical resistivity in Ω·mm2/m (20 °C)
0.3
Electrical resistivity in Ω·mm2/m (100 °C)
0.308
Electrical resistivity in Ω·mm2/m (200 °C)
0.315
Electrical resistivity in Ω·mm2/m (300 °C)
0.323
Electrical resistivity in Ω·mm2/m (400 °C)
0.331
Electrical resistivity in Ω·mm2/m (500 °C)
0.339
Alloy Identification Symbol
CuNi30-Mn
Electrical resistivity in Ω·mm2/m (20 °C)
0.4
Electrical resistivity in Ω·mm2/m (100 °C)
0.404
Electrical resistivity in Ω·mm2/m (200 °C)
0.41
Electrical resistivity in Ω·mm2/m (300 °C)
0.417
Electrical resistivity in Ω·mm2/m (400 °C)
0.424
Electrical resistivity in Ω·mm2/m (500 °C)
0.432
Alloy Identification Symbol
CuNi44
Electrical resistivity in Ω·mm2/m (20 °C)
0.49
Electrical resistivity in Ω·mm2/m (100 °C)
0.49
Electrical resistivity in Ω·mm2/m (200 °C)
0.49
Electrical resistivity in Ω·mm2/m (300 °C)
0.49
Electrical resistivity in Ω·mm2/m (400 °C)
0.49
Electrical resistivity in Ω·mm2/m (500 °C)
0.49

Table Credit: https://www.copper.org/applications/marine/cuni/properties/DKI_booklet.html#gen

How Is the Corrosion Resistance of Copper Nickel Alloy?

Copper-nickel (CuNi) alloys have very good corrosion resistance, especially against seawater. The corrosion resistance of CuNi alloys is primarily attributed to the protective oxide layer that forms on their surface when exposed to air or moisture. This oxide layer acts as a barrier, preventing further corrosion and rust formation. 

What Are the Physical Properties of Copper Nickel Alloys?

The physical properties of CuNi alloys are outlined in Table 2 below. The minimum and the maximum values outline the range in which these CuNi alloys typically fall.  For more information, see our guide on Metalloids Properties.

Table 2: Physical Properties of CuNi Alloys
PropertyMinimum ValueMaximum ValueUnit
Property
Average Atomic Volume
Minimum Value
0.0071
Maximum Value
0.0073
Unit
m3/kmol
Property
Density
Minimum Value
8.5
Maximum Value
8.95
Unit
Mg/m3
Property
Latent Heat of Fusion
Minimum Value
220
Maximum Value
240
Unit
kJ/kg
Property
Melting Point
Minimum Value
1384
Maximum Value
1508
Unit
K
Property
Specific Heat
Minimum Value
384
Maximum Value
386
Unit
J/kg·K
Property
Thermal Conductivity
Minimum Value
19
Maximum Value
66
Unit
W/m·K

Table Credit: https://www.nickel-alloys.net/article/copper-nickel-alloys-alloys-with-copper.html

What Is the Mechanical Properties of Copper Nickel Alloys?

Copper-nickel (CuNi) alloys possess a range of mechanical properties that make them suitable for a number of applications. The specific mechanical properties can vary depending on the alloy grade and heat treatment, but some typical values are outlined in Table 3.

Table 3: Mechanical properties of CuNi alloys.
PropertyMinimum ValueMaximum ValueUnit
Property
Bulk Modulus
Minimum Value
130
Maximum Value
170
Unit
GPa
Property
Compressive Strength
Minimum Value
85
Maximum Value
550
Unit
MPa
Property
Ductility
Minimum Value
3
Maximum Value
44
Unit
%
Property
Yield Strength
Minimum Value
85
Maximum Value
550
Unit
MPa
Property
Fracture Toughness
Minimum Value
26
Maximum Value
79
Unit
MPa·m1/2
Property
Poisson's Ratio
Minimum Value
0.34
Maximum Value
0.35
Unit
-
Property
Shear Modulus
Minimum Value
45
Maximum Value
58
Unit
GPa
Property
Tensile Strength
Minimum Value
267
Maximum Value
624
Unit
MPa
Property
Young’s Modulus
Minimum Value
120
Maximum Value
156
Unit
GPa

Does CuNi Alloy Rust?

No, copper-nickel alloys do not rust because they are not iron or steel, and the term only applies to iron-based alloys. Plain-carbon steels do not have an adherent oxide, which severely limits their corrosion resistance potential. CuNi alloys, on the other hand, have a tightly adherent, protective oxide. As a result, they are well-suited for applications that demand long-term durability, including the construction of saltwater pipelines and marine vessels.

Is Copper Nickel Alloy Expensive?

Yes, copper-nickel alloys are expensive. The cost of copper-nickel (CuNi) alloys can vary depending on several factors, including the specific alloy grade, market conditions, and the quantity and form of the material being purchased. Generally speaking, CuNi alloys tend to be more expensive than stainless steel. 

Is CuNi Alloy Safe?

Yes, copper-nickel alloys are considered safe for many applications, with some important caveats. In terms of human health, CuNi alloys are generally safe. Copper and nickel are naturally occurring elements found in the environment, food, and water. However, prolonged exposure to high concentrations of copper or nickel dust, fumes, or particles in industrial settings can pose health risks. It is important to follow safety measures, such as ensuring proper ventilation and wearing personal protective equipment when handling CuNi materials.

What Is the Difference Between Copper Nickel Alloy and Alloy Steel?

Copper-nickel alloys and alloy steels are distinct materials with different compositions, properties, and applications. Copper-nickel alloys primarily consist of copper and nickel as the main alloying elements. In contrast, alloy steels are iron-based and encompass a range of steel compositions with various alloying elements, such as carbon, chromium, molybdenum, and manganese. While copper-nickel alloys excel in corrosion resistance, alloy steels are sought after for their mechanical properties. The choice between these materials depends on the specific requirements of the application at hand, be it corrosion resistance or mechanical strength.

Summary

This article presented copper-nickel alloys, explained what it is, and discussed its various applications and advantages. To learn more about copper-nickel alloys, contact a Xometry representative.

Xometry provides a wide range of manufacturing capabilities and other value-added services for all of your prototyping and production needs. Visit our website to learn more or to request a free, no-obligation quote.

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Xomety X
Team Xometry
This article was written by various Xometry contributors. Xometry is a leading resource on manufacturing with CNC machining, sheet metal fabrication, 3D printing, injection molding, urethane casting, and more.

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