A nickel alloy is a metal that contains a percentage of nickel in its elemental makeup. Nickel is primarily alloyed with chromium, copper, iron, titanium, and molybdenum. Each of these alloy combinations has specific properties that make it best suited to a certain range of applications. For example, Inconel® has excellent corrosion, oxidation, and high-temperature resistance. Most nickel alloys exhibit good corrosion, oxidation, and high-temperature strength properties, with some exceptions. Nickel-iron alloys do not have the same levels of corrosion and oxidation resistance. Nickel alloys are often used in extreme working environments, such as those encountered in the aerospace, chemical processing, and petroleum industries but can also be used in electrical and electronics applications.
Learn more about this material, including its history and how it’s used in manufacturing.
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This article will describe what a nickel alloy is, where it is used, it’s characteristics and physical properties, as well as the different types of nickel alloys and their uses.
What Is a Nickel Alloy?
The term nickel alloy refers to a metal that has nickel as one of its primary elements. Some types of nickel alloys are referred to as superalloys because of their superior oxidation and creep resistance, allowing them to be used at temperatures of more than half their melting points. Nickel alloys can be machined and welded but tend to pose some processing difficulties, as some alloys will work harden during machining, and their high melting points can make them difficult to weld.
What Is the History of Nickel Alloys?
The earliest record of the use of a potential nickel alloy was in China in 200 BCE, which spoke of a material called “white copper,” (most likely a nickel-silver alloy). In 1751, German scientist Axel Fredrik Cronstedt was able to isolate nickel from a mineral called niccolite. The first nickel alloys contained copper and zinc. They were referred to as “German silver.” These early alloys were primarily used as ornamental materials.
Following the work of James Riley in 1913, who produced an iron-chromium alloy, Dr. W.H. Hatfield discovered the benefits of adding nickel to these iron-chrome alloys to create austenitic stainless steel as it is known today, with its excellent corrosion resistance.
What Is the Other Term for Nickel Alloy?
The vast majority of metals termed superalloys are nickel-based. Another term often used to describe nickel alloys is high-performance alloys. However, it is important to note that not all superalloys are nickel alloys.
What Are Nickel Alloys Made Of?
Nickel alloys are typically made from a mixture of various metals and nickel. Although not all metals can be effectively combined with nickel. Some of the most common elements that can be alloyed with nickel are iron (Fe), chromium (Cr), aluminum (Al), molybdenum (Mo), copper (Cu), cobalt (Co), and titanium (Ti). These elements can be combined to produce alloys with different properties. For example, nickel, iron, molybdenum, and chromium alloys, such as stainless steel Type 316, have excellent corrosion resistance.
How Are Nickel Alloys Made?
Nickel alloys are made with the same process used for most other metal alloys. The alloying elements must be chosen and their ratios must be confirmed. Next, the elements are all melted together in an arc furnace, for example. During smelting, the alloys are also purified. The nickel alloy is then cast into ingots after which it is formed using cold or hot working techniques.
What Are the Characteristics of Nickel Alloys?
Listed below are some common characteristics of nickel alloys:
- Corrosion Resistance: Nickel alloys have excellent resistance to corrosion and oxidation, making them ideal for use in harsh environments.
- High Strength: Nickel alloys can have high strength. For that reason, they are especially beneficial where high strength and toughness are needed at elevated temperatures.
- Heat Resistance: Nickel alloys have excellent heat resistance and can continuously withstand temperatures as high as 980 °C, in the case of Inconel® 718.
- Ductility: Nickel alloys are highly ductile, and as such are very tough materials, able to withstand impacts without breaking suddenly.
- Magnetic Properties: Nickel alloys, especially those with very high levels of nickel have excellent soft magnetic properties, which means they can be easily magnetized and demagnetized. Nickel alloys can be said to have low coercivity (a measure of the difficulty of demagnetizing a magnetic material).
- Weldability: Nickel alloys can be welded using the MIG (metal inert gas) or TIG (tungsten inert gas) processes. They can also be joined using MMA (manual metal arc) welding. Nickel alloys can be difficult to weld, and issues such as hot or warm cracking and porosity are common.
- Thermal Conductivity: Nickel alloys do not have particularly good thermal conductivity. However, low thermal conductivity is often desired in high-temperature applications to limit heat transfer to other components. However, nickel-copper alloys can be used if thermally conductive behavior is required.
- Electrical Conductivity: Nickel alloys have lower electrical conductivity than pure copper or silver. Nickel copper alloys do, however, have improved electrical conductivity along with increased corrosion resistance.
- Low Thermal Expansion Coefficient: Nickel alloys typically have low thermal expansion coefficients. This makes them ideal for precision applications that must maintain dimensional stability over a range of temperatures.
What Is the Color of Nickel Alloy?
The color of a nickel alloy depends entirely on its specific composition. Natural nickel has a silver-white appearance, and nickel alloys will have a similar color depending on their nickel content. Electroless nickel coatings can have a golden-brown appearance due to the presence of phosphorus in the coating.
What Does a Nickel Alloy Look Like?
In general, it may be difficult to differentiate nickel alloys from other metals which also have a metallic appearance. Nickel alloys can have a silver-white appearance, but this is highly dependent on the surface finish and composition of the alloy. A rough surface will give a dull appearance, whereas a smooth surface may appear reflective. Figure 1 below is an example of a nickel-chromium alloy:
What Are the Different Types of Nickel Alloys?
There is a wide range of nickel alloys available. Some of the common grades are listed below:
1. Inconel®
Inconel® is a trade name for a type of nickel alloy that contains chromium, molybdenum, and iron as its main alloying elements. It is known for its oxidation resistance, excellent performance in a high-temperature environment, and mechanical strength. Inconel® can be difficult to cold form due to its rapid work-hardening behavior. Typical alloys are Inconel 625, 718, and 600.
2. Monel®
Monel® is a trade name for a group of copper-based nickel alloys. Monel has high strength and excellent saltwater resistance, as well as the ability to perform well in low-temperature environments, i.e there is not a large reduction in ductility and there is an increase in hardness and strength. Monel® tends to work harden during cold forming, making it difficult to process. Typical alloys are Monel® 400, R-405, and K-500.
3. Hastelloy®
Hastelloy® is the trade name for a highly corrosion-resistant alloy of either a nickel-chromium alloy or a nickel-molybdenum alloy. In addition, Hastelloy® also has good thermal stability and is used in the aerospace and chemical processing industries. Typical alloys include C-22 and C-276.
4. Nickel-Copper Alloys
Nickel-copper alloys have excellent saltwater corrosion and fouling resistance. For that reason, they are used extensively in the marine industry. Iron, tin, and manganese are sometimes added to further improve corrosion resistance. The copper content can be anywhere from 55 to 91.5%, with nickel being the next largest alloying element. The other alloying elements make up a small percentage of the total weight. Monel® is considered a nickel-copper alloy.
5. Nickel-Iron Alloys
Nickel-iron alloys have good ductility, low thermal expansion, and corrosion resistance. These alloys also have soft magnetic properties. These alloys are used in applications where low thermal expansion is desired like sensitive scientific equipment or where soft magnetic properties are beneficial, for example in transformers. A common trade name for a nickel-iron alloy is Invar®.
6. Nickel-Chromium Alloys
Nickel chromium alloys have excellent corrosion and oxidation resistance while also maintaining their strength at elevated temperatures. They also have high electrical resistivity. This makes nickel-chromium alloys especially fit for application as heater elements, such as those found in ovens or toasters, for example. Nickel chromium alloys can have a melting point of over 1300 °C. These alloys typically have a high nickel content, 70%.
7. Nickel-Titanium Alloys
Nickel-titanium alloys have excellent corrosion resistance and good mechanical strength. However, the most interesting property is that they are a type of shape memory alloy (SMA). They can be formed into a specific shape above a certain high temperature, called the transition temperature. When cool, the part can be deformed to a certain degree, but if it is heated back up to its transition temperature, it will resume its original shape. The exact temperature at which this change takes place can be adjusted by changing the composition of the alloy. These alloys are especially useful in medical applications. For example, stents can be inserted in their compressed form but will expand to their final shape once in the body. Nickel-titanium alloys are also known by the name Nitinol®.
8. Nickel-Molybdenum Alloys
Nickel molybdenum alloys have excellent corrosion and oxidation resistance at high temperatures. They also maintain their mechanical properties at elevated temperatures. A common nickel-molybdenum alloy is also known as Hastelloy®. This nickel alloy is often used for heat exchangers, pumps, and reactor pressure vessels.
What Are the Properties of Nickel Alloys?
Nickel alloys can withstand high operating temperatures and corrosive environments, and have good mechanical strength. In addition to this, they can have soft magnetic behavior, low thermal conductivity, and good electrical conductivity. Table 1 below lists the properties of nickel alloys:
Table 1: Nickel Alloys Properties
| Property | Description | Nickel Alloy Example | Additional Advantages | Applications |
|---|---|---|---|---|
| Ultimate Tensile Strength [MPa] | The stress that would cause ultimate failure when loaded in pure tension | Inconel 625 | Excellent corrosion and oxidation resistance, High creep strength | Aerospace components such as turbine blades |
| Curie Temperature [°C] | Temperature where a material loses its magnetism | Invar 36 | Low Thermal conductivity | Tooling, dies, cryogenic components |
| Coefficient of Linear Thermal Expansion @ @ 93 °C (Annealed) (µm/µm·°C) | The degree of linear expansion of a sample at 93C | Invar 36 | High melting temperature | Tooling, dies, cryogenic components |
| Thermal Conductivity @ 93 °C (Annealed) (W/m·K) | The ability of a material to absorb and transfer heat | Monel 400 | Excellent salt water resistance and low-temperature strength | Process vessels, process piping, pumps |
What Are the Physical Properties of Nickel Alloys?
Listed below in Table 2 are the physical properties of some common nickel alloys:
Table 2: Nickel Alloy Physical Properties
| Property | Description | Inconel® 625 | Hastelloy® 276 | Invar® 36 | Monel® 400 | Nichrome 35-20 |
|---|---|---|---|---|---|---|
| Density [g/cm3] | Defines the compactness of the atoms | 8.44 | 8.89 | 8.05 | 8.8 | 7.9 |
| Ultimate Tensile Strength [MPa] | The stress that would cause ultimate failure when loaded in pure tension | 689 – 1103 | 601.2 – 826.7 | 621 | 450 – 550 | 750 |
| Curie Temperature [°C] | Temperature where a material loses its magnetism | -196 | -269 > 26.85 | 279 | 20-50 | NA |
| Melting Temperature [°C] | The temperature at which a material will begin to transition to a liquid form | 1290 – 1350 | 1323 – 1271 | 1427 | 1300-1350 | 1390 |
| Electrical Resistivity @ 93 °C (Annealed) [µΩ·cm] | How strong a material resist the flow of electricity | 132 | 130 | 82 | 54.7 | 104 |
| Coefficient of Linear Thermal Expansion @ @ 93 °C (Annealed) (µm/µm·°C) | The degree of linear expansion of a sample at 93C | 12.8 | 11.2 | 1.3 | 13.9 | 19 |
| Thermal Conductivity @ 93 °C (Annealed) (W/m·K) | The ability of a material to absorb and transfer heat | 10.8 | 11.1 | 10.15 | 21.8 | 13 |
| Specific Heat @ 93°C (Annealed) (J/kg·°C) | Amount of energy needed to increase the temperature of a kilogram of material by 1C | 427 | 427 | 515 | 427 | 500 |
Table Credit: https://matweb.com/
What Are the Chemical Properties of Nickel Alloys?
Table 3 lists some chemical properties of various nickel alloys:
Table 3: Nickel Alloy Chemical Properties
| Nickel Alloy Type | Corrosion Resistance | Oxidation Resistance | Main Alloying Elements | Magnetic | Heat Resistance [Solidus] °C |
|---|---|---|---|---|---|
| Inconel® 625 | Very resistant to pitting, chloride ion stress corrosion cracking, and crevice corrosion | Highly resistant to oxidation at elevated temperatures | Ni – 58% / Cr – 20 to 23% / Fe – 5% / Nb,Ta – 3.15 to 4.15% | No | 1290 |
| Hastelloy® 276 | Very resistant to pitting, chloride ion stress corrosion cracking, and crevice corrosion | Highly resistant to oxidation at elevated temperatures | Ni – 57% / Mo – 15 to 17% / Cr – 14.5 to 16.5% / Fe – 4 to 7% / Co – 2.5% / Mn – 1% | No | 1323 |
| Invar® 36 | Not corrosion resistant due to high iron content; must be nickel plated to improve corrosion resistance | Not particularly resistant to oxidation due to iron content when compared to other nickel alloys | Fe – 63% / Ni – 36% | Yes | 1427 |
| Monel® 400 | Highly resistant to saltwater environments | Some Monel grades can have good high-temperature oxidation resistance. | Ni – 63% / Cu – 28 to 34% / Fe – 2.5% / Mn – 2% | No | 1300 |
| Nichrome 35 -20 | Not very corrosion resistant | Not very resistant to oxidation | Fe – 42% / Ni – 35% / Cr – 20% / Si – 2% / Mn – 1% | No | 1390 |
Table Credit: https://matweb.com/
What Are the Applications of Nickel Alloy?
Nickel alloys are widely used in a number of industries. Listed below are some typical applications of the various alloys:
1. Aerospace
The aerospace industry is one of the largest users of nickel-based alloys because of the high operating temperatures common on high-performance aerospace equipment. Turbine blades and rocket engine components are often manufactured from alloys like Inconel®.
2. Chemical Processing
The chemical processing industry often requires materials that are highly resistant to corrosive environments. Nickel alloys have exceptional corrosion resistance, especially when alloyed with elements such as chromium and nickel, high iron content alloys can have reduced corrosion resistance. Typical applications can include tanks, piping, and mixing devices.
3. Oil and Gas
The oil and gas industry is complex and involves everything from the extraction of oil to the processing of fuels, plastics, and other complex materials. Because of that, materials are often required to withstand high temperatures and pressures, and corrosive environments. Nickel alloys are a good fit for these situations. Typical applications can include pumps, pipes, pressure vessels, and heat exchangers.
4. Medical Equipment
Medical equipment, such as surgical instruments, must often be sterilizable either with strong solvents or high temperatures. Nickel alloys are ideal for this service environment. Shape memory alloys like Nitinol® are also popular for stents, as they can be implanted in a collapsed state and expand once in position. Nickel alloys are also used for orthopedic implants.
5. Electrical and Electronic Applications
Nickel alloys like Monel®, which are alloyed with copper, offer good electrical conductivity with the added benefit of corrosion resistance. For those reasons, these alloys are ideal for electrical contacts in corrosive environments. Some nickel alloys, such as Ni-Fe alloys have low coercivity which makes them ideal for soft magnetic applications like transformers or memory storage devices.
6. Marine Applications
Marine environments can be extremely corrosive. Not many alloys can withstand prolonged exposure to salt water and salt spray. Nickel alloys, especially when alloyed with copper, are highly resistant to marine environments. Typical applications can include propellers, bilge pumps, and valves.
7. Precision Instruments
Some precision instruments need to have a very low coefficient of thermal expansion to limit the effect of temperature on sensitive applications. An example of such an application is hermetic seals in X-ray tubes. In other cases, the low thermal expansion nickel alloy is used in conjunction with a high thermal expansion metal, joined into a bimetal strip, for use as a temperature switch.
What Are the Benefits of Nickel Alloys?
Here are some of the key benefits of using nickel alloys:
- Corrosion Resistance: Nickel alloys have excellent resistance to corrosion and oxidation, making them highly desirable in environments where other materials would quickly degrade.
- High Strength: Nickel alloys have high tensile strength and can withstand high temperatures and extreme conditions, making them suitable for use in critical components and applications.
- Soft Magnetic Properties: Some nickel alloys exhibit excellent soft magnetic properties, with low coercivity. This means they can be easily magnetized and demagnetized.
- Heat Resistance: Nickel alloys have very high-temperature resistance. They can maintain their properties at higher temperatures and also prevent heat transfer to other components due to the low thermal conductivity of some nickel alloys.
- Low Thermal Expansion: Some nickel alloys have a very low rate of thermal expansion. This characteristic is especially useful in precision applications where thermal effects have a chance of negatively affecting performance.
What Are the Limitations of Nickel Alloys?
Here are some of the limitations of nickel alloys:
- Cost: Nickel alloys can be more expensive than other metals due to the high cost of nickel and other alloying elements. For this reason, they are often only applicable to high-performance applications such as those found in the aerospace industry, for example.
- Machinability: Some nickel alloys can be difficult to machine because of their high strength and toughness. In addition, nickel alloys tend to work harden during machining. They often require special tools and techniques to process.
- Weldability: Some nickel alloys can be difficult to weld due to their high melting points. The high melting temperature means that more heat must be added to the workpiece to get an adequate pool of weld metal to make a good joint. This additional energy can induce residual stresses that cause deformation of the welded component.
- Dermatitis: Some nickel alloys can cause an allergic reaction when in long-term contact with the skin. This limits their potential applications in terms of wearables or medical devices.
- Tarnish: Some nickel alloys will tarnish over time when exposed to the elements. Copper-based nickel alloys are typically prone to tarnishing.
Are Nickel Alloys Rust Proof?
Yes, most nickel alloys like stainless steel have excellent corrosion resistance and can be exposed to extreme environments for long periods without oxidizing. This is because they form a highly corrosion-resistant oxide layer.
Are Nickel Alloys Hypoallergenic?
No, nickel is known to cause allergic skin reactions.
Are Nickel Alloys Metals?
Yes, all nickel alloys can be classified as metals. Nickel alloys are a mixture of two or more elements, one of which is nickel, to create unique material properties not present in the individual materials.
What Is the Difference Between a Nickel Alloy and a Metal?
There is no difference between “a nickel alloy” and “a metal”. A nickel alloy is a metal.
What Is the Difference Between a Nickel Alloy and Aluminum?
Nickel alloys typically contain the element Ni (nickel), along with other elements such as copper (Cu), chromium (Cr), molybdenum (Mo), and iron (Fe). Aluminum is a completely different metal that can also be alloyed with other metals and is sometimes used in nickel alloys as an alloying element.
Copyright and Trademark Notices
- Inconel® and Monel are trademarks of INCO ALLOYS INTERNATIONAL.
- Hastelloy® is a trademark of HAYNES STELLITE COMPANY.
- Invar® is a trademark of STE. AME. DE COMMENTRY FOURCHAMBAULT ET DECAZEVILLE.
- Nitinol® is a trademark of Nitinol Devices and Components, Inc.
