Nickel Alloys: Definition, Properties, Types, Composition, Advantages, and Applications

A nickel alloy refers to a metallic substance that contains a specific proportion of nickel within its elemental composition. Nickel is predominantly combined with chromium, copper, iron, titanium, and molybdenum in the form of alloys. Each of these alloy combinations possesses distinct properties that render it most suitable for a particular range of applications. As an example, Inconel® exhibits exceptional resistance to corrosion, oxidation, and elevated temperatures. The majority of nickel alloys demonstrate favorable characteristics in terms of corrosion resistance, oxidation resistance, and strength at elevated temperatures, although there are a few exceptions. Nickel-iron alloys exhibit varying degrees of corrosion and oxidation resistance. They are frequently employed in highly demanding operational conditions, exemplified by the aerospace, chemical processing, and petroleum sectors, while also finding utility in the electrical and electronics domains.

Nickel, a highly versatile metallic element, is abundantly present in both the earth’s crust and core. Nickel possesses a range of advantageous characteristics that contribute to its practicality in various industrial contexts. It should be noted that nickel possesses a high degree of ductility, rendering it a highly desirable element for use in alloys to modify the characteristics of various other metals.

What is Nickel alloy?

It is a type of metal that consists of nickel in addition to at least one additional element, such as iron, copper, or titanium. Nickel is the predominant component of a nickel alloy. These alloys can be fashioned into a wide variety of forms, including wires and sheets, pipelines and housing for electrical equipment, and housing for electronic devices. They are renowned for their outstanding corrosion resistance, strength at high temperatures, and great mechanical qualities. Because of this, nickel alloy is a common material choice for a diverse variety of applications, such as in the aerospace industry, the processing of chemicals, marine engineering, and the production of energy.

 As a result of their biocompatibility and resistance to corrosion caused by body fluids, nickel alloys are frequently utilized in the production of medical devices. It should come as no surprise that nickel alloys have become one of the most essential materials in current industrial applications given the exceptional qualities and adaptability that these alloys possess.

Properties of Nickel Alloy

• Corrosion Resistance: The corrosion and oxidation resistance of nickel alloys makes them well suited for use in severe conditions.
• High Strength: They possess the capability to exhibit exceptional levels of mechanical strength. Therefore, these materials are particularly advantageous in situations requiring higher temperature resistance and a combination of high strength and toughness.
• Heat resistance: They exhibit exceptional thermal resistance properties, enabling them to sustain elevated temperatures up to 980 °C without interruption, as exemplified by the performance of Inconel® 718.
• Ductility: They exhibit a high degree of ductility, rendering them exceptionally resilient materials capable of withstanding impacts without experiencing a sudden fracture.
• Magnetic properties: Nickel alloys, particularly those with elevated nickel content, exhibit exceptional soft magnetic characteristics, rendering them highly susceptible to magnetization and demagnetization processes. They can be characterized by their relatively low coercivity, which is a measure used to quantify the resistance of a magnetic material to demagnetization.
• Thermal conductivity: They exhibit relatively low thermal conductivity. Nevertheless, there is often a preference for low thermal conductivity in high-temperature applications in order to restrict the transfer of heat to other components. Nevertheless, in situations where thermal conductivity is necessary, nickel-copper alloys can be employed.
• Electrical conductivity: Nickel alloys exhibit a reduced level of electrical conductivity in comparison to that of pure copper or silver. However, it should be noted that nickel-copper alloys exhibit enhanced electrical conductivity as well as increased resistance to corrosion.
• Weldability: The welding of nickel alloys can be accomplished through the utilization of the MIG (metal inert gas) or TIG (tungsten inert gas) processes. Additionally, the joining process of MMA (manual metal arc) welding can be employed. Welding nickel alloys presents challenges, as it often involves encountering prevalent concerns such as hot or warm cracking and porosity.
• Low thermal expansion coefficient: Nickel alloys generally exhibit low coefficients of thermal expansion. This characteristic renders them well-suited for precision applications that necessitate the preservation of dimensional stability across a spectrum of temperatures.

Composition of Nickel alloy

Undoubtedly, the fundamental constituent present in all nickel alloys is nickel. This resilient metallic material possesses remarkable resistance to corrosion, oxidation, and high temperatures, while also exhibiting a notable level of ductility and formability. Nickel alloys are widely favored in various industries and sectors, which is not surprising given their exceptional properties and versatility. It is estimated that on an annual basis, approximately 90% of the total nickel sold is specifically acquired for the purpose of alloy production.

In the realm of nickel alloy fabrication, the incorporation of nickel with various metals, in varying proportions, enables the generation of a substance possessing distinct characteristics. The following are several frequently encountered options, accompanied by a selection of their respective attributes.

• Titanium: The utilization of lightweight materials with high-strength properties has been observed to enhance both strength and corrosion resistance under elevated temperature conditions.
• Copper: The material under consideration possesses non-magnetic properties, exhibits excellent machinability, and demonstrates exceptional heat and electrical conductivity.
• Cobalt: In highly elevated temperatures, it exhibits exceptional resistance to corrosion.
• Chromium: It enhances the ability to resist corrosion and stress-induced cracking.
• Aluminum: The addition of certain elements increases the structural integrity and improves the ability of the material to resist corrosion.
• Niobium: The addition of this substance enhances weldability and enhances mechanical properties.

Types of Nickel Alloys

1. Nickel-Copper Alloys

Nickel-copper alloys exhibit exceptional resistance to corrosion and fouling in saltwater environments. Hence, their widespread utilization is prevalent within the marine sector. In order to enhance the resistance to corrosion, iron, tin, and manganese are occasionally incorporated as additional elements. The copper content ranges from 55% to 91.5%, with nickel being the second most significant alloying element. The remaining alloying elements constitute a minor proportion of the overall mass. Monel® is widely recognized as a type of alloy composed of nickel and copper.

2. Nickel-iron alloys

Nickel-iron alloys are corrosion-resistant, ductile, and low-expansion. These alloys are a soft magnet. In delicate scientific equipment and transformers, these alloys have low thermal expansion and gentle magnetic characteristics. Nickel-iron alloys are called Invar®.

3. Nickel-Chromium Alloys

Nickel chromium alloys are strong and corrosion-resistant at high temperatures. They have high electrical resistance. Nickel-chromium alloys are ideal heater elements for ovens and toasters. Nickel-chromium alloys melt above 1300 °C. These alloys contain 70% nickel.

4. Nickel-Titanium Alloys

Nickel-titanium alloys are corrosion-resistant and strong. Their shape memory alloy (SMA) status makes them most intriguing. Above the transition temperature, they can be shaped. If heated to its transition temperature, the part will return to its former shape. The alloy’s composition determines the change’s temperature. These alloys are useful in medicine. Stents can be injected compressed but expand in the body. Nitinol® alloys are nickel-titanium.

5. Nickel-Molybdenum Alloys

Nickel-molybdenum alloys resist high-temperature corrosion and oxidation. They retain mechanical characteristics at high temperatures, and Nickel-molybdenum alloy Hastelloy® is common. Heat exchangers, pumps, and reactor pressure vessels use nickel alloy.

6. Nickel-Chromium-Iron Alloys

Nickel-chromium-iron alloys are resistant to oxidation and high-temperature corrosion because they incorporate these components. These alloys are also valued for their superior creep and rupture characteristics at extreme heat. These alloys include a minimum of 39.5% Iron and often contain 30-35% Nickel and 19-23% Chromium.

7. Nickel-Chromium-Molybdenum Alloys

Nickel-chromium-molybdenum alloys are also resistant to reducing acids like hydrochloric and sulfuric acid. This alloy contains nickel, 15-17% molybdenum, 14.5-16.5% chromium, 4-7% iron, 3-4.5% tungsten, and lower amounts of manganese.  Heat exchangers, evaporators, reaction vessels, pollution control stack liners, ducts, and scrubbers use this alloy.

8. Nickel-Chromium-Cobalt Alloys

Nickel alloys with additional chromium and molybdenum have increased creep rupture strength. Components in industrial furnaces, gas turbines, catalyst grid support for nitric acid synthesis, and fossil fuel production facilities all make use of these alloys.

Advantages of Nickel Alloy

• Magnetism: Nickel alloys possess magnetic properties, rendering them highly suitable for a diverse range of applications that necessitate magnetism, including but not limited to electric motors and generators.
• Temperature Resistance: In addition to their high-temperature resistance, nickel alloys also exhibit resistance to elevated temperatures. These properties render them highly suitable for utilization in various applications, including furnace linings and turbochargers, wherein they can endure temperatures reaching 1200 degrees Celsius.
• High durability: Nickel alloys are renowned for their enhanced durability in comparison to alternative metallic materials. The reason for this phenomenon can be attributed to the inherent strength of nickel as a metal, which renders it highly resistant to both corrosion and wear. Nickel alloys possess advantageous properties that render them highly suitable for deployment in scenarios characterized by severe environmental conditions, such as those encountered in the automotive or aerospace sectors.
• Less expansion rate: Nickel alloys exhibit a low coefficient of thermal expansion, indicating their resistance to substantial alterations in shape or dimensions upon exposure to variations in temperature. The aforementioned characteristic renders them highly suitable for utilization in various applications, including optical systems and medical implants, wherein a minimal expansion rate holds utmost significance.
• Good thermal conductivity: An additional benefit associated with nickel alloys is related to their enhanced thermal conductivity. This implies that they possess the capability to efficiently eliminate heat from delicate components, rendering them well-suited for utilization in scenarios involving elevated temperatures. Moreover, it is worth noting that nickel alloys exhibit a superior melting point in comparison to other metallic materials, thereby rendering them less susceptible to deformation when exposed to elevated temperatures.
• High strength: Nickel alloys are widely recognized for their enhanced mechanical strength and exceptional durability. This characteristic renders them highly suitable for a diverse range of applications, including the construction of buildings and bridges. Nickel alloys are frequently employed in the fabrication of machinery and equipment due to their ability to endure significant levels of mechanical stress and abrasion.
• Increased electrical conductivity: In comparison to other metals, nickel alloys exhibit superior electrical conductivity. This characteristic renders them highly suitable for utilization in electrical applications that necessitate elevated levels of conductivity, such as batteries or electrical wiring. Moreover, nickel alloys possess non-magnetic properties, rendering them well-suited for utilization in contexts where magnetism is undesirable, such as the field of medical devices.
• Corrosion resistance: In comparison to other metals, nickel alloys exhibit enhanced resistance to corrosion. The formation of a protective oxide layer on the surface of nickel when it comes into contact with oxygen is responsible for inhibiting subsequent corrosion processes. Moreover, it should be noted that nickel alloys exhibit remarkable resistance to stress corrosion cracking, rendering them highly suitable for applications involving elevated pressures.
• Recyclability: Nickel alloys also have the benefit of being easily recyclable. More than sixty percent of all nickel alloy products are manufactured using secondary nickel. This makes nickel alloys a viable option for individuals concerned about their environmental footprint.

Disadvantages of nickel alloy

• Cost: Nickel alloy has the drawback of being more expensive than other metals. Since nickel is so uncommon, its production costs are higher than those of more common metals. The fact that nickel alloy is so challenging to weld and repair further contributes to the material’s high price.
• Weldability: Repairs can be challenging when working with nickel alloy because it is tough to weld. Welding nickel alloy requires a filler metal that is chemically and structurally comparable to the base metal. If not, the weld might not hold and will eventually fall apart.
• Machinability: Nickel alloys that are very strong and resistant might be challenging to manufacture. Nickel alloys also have a tendency to work harden throughout the machining process. They usually need to be handled using specialized equipment and methods.
• Allergic reaction: The increased potential for allergic reactions is one of nickel alloy’s main drawbacks. Skin irritation, rashes, and swelling can result from contact with nickel alloy, as nickel is a known allergy. Anaphylactic shock, a potentially fatal allergic reaction, can occur in people who are exposed to nickel alloy.
• Tarnish: When left out in the weather, nickel alloys can tarnish over time. Nickel alloys based on copper tend to oxidize easily.
• Environmental issue: Last but not least, the manufacturing of nickel alloys is fraught with environmental risks. Pollutants in the air and water may result from the extraction and processing of nickel ore.

Application of Nickel Alloy

• Due to the high working temperatures typical of high-performance aircraft equipment, the aerospace sector is one of the greatest users of nickel-based alloys. Alloys like Inconel® are commonly used in the production of turbine blades and rocket engine components.
• Corrosion-resistant materials are frequently needed in the chemical processing industry. Even when alloyed with chromium and nickel, high iron content alloys can have diminished corrosion resistance, yet nickel alloys have remarkable corrosion resistance on their own. Tanks, pipelines, and mixers are some common examples of where this is used.
• The oil and gas sector encompasses a wide range of activities, from drilling for oil to refining fuels and plastics. For this reason, it’s important to find materials that can hold up under extreme conditions. Nickel alloys work well in these kinds of conditions. Pumps, pipes, pressure containers, and heat exchangers are only few of the commonplace uses.
• Instruments used in surgery, for example, must be able to survive being subjected to high temperatures or corrosive solvents for sterilization. Nickel alloys perform exceptionally well in these conditions. Stents made from shape memory alloys like Nitinol® are also quite common because of their ability to be implanted in a compressed form and then expanded into their intended shape once in place. Orthopedic implants made of nickel alloys are also in use.
• Corrosion is a common problem in marine areas. In general, salt water and salt spray are not friendly to most alloys. Nickel alloys, particularly those alloyed with copper, have excellent corrosion resistance in salt water. Propellers, bilge pumps, and valves are all examples of common uses.
• In order to minimize the impact of temperature changes on sensitive applications, a very small coefficient of thermal expansion is required of some precision equipment. Hermetic sealing in X-ray tubes are one such use. Nickel alloys with minimal thermal expansion are sometimes utilized as temperature switches when combined with metals with strong thermal expansion in the form of a bimetal strip.
• Alloying nickel and copper creates nickel alloys like Monel®, which have excellent electrical conductivity and are also resistant to corrosion. Because of their resistance to corrosion, these alloys are frequently used as electrical contacts in harsh conditions.

References

• https://blog.thepipingmart.com/metals/nickel-alloys-a-comprehensive-overview/
• https://blog.thepipingmart.com/metals/advantages-and-disadvantages-of-nickel-alloy/#:~:text=Nickel%20alloys%20are%20known%20for%20their%20increased%20strength%20and%20durability,levels%20of%20wear%20and%20tear.
• https://www.xometry.com/resources/materials/what-is-nickel-alloy/
• https://continentalsteel.com/nickel-alloys/
• https://www.nickel-alloys.net/article/nickel-alloys-stainless-steels-nickel.html
• https://www.corrotherm.co.uk/blog/what-are-nickel-alloys
• https://www.thomasnet.com/articles/metals-metal-products/types-of-nickel-alloys/