Nickel Alloy: Definition, Composition, Types, Properties, ...

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.

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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. 

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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:

1. Corrosion Resistance: Nickel alloys have excellent resistance to corrosion and oxidation, making them ideal for use in harsh environments.
2. 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.
3. Heat Resistance: Nickel alloys have excellent heat resistance and can continuously withstand temperatures as high as 980 °C, in the case of Inconel® 718.
4. Ductility: Nickel alloys are highly ductile, and as such are very tough materials, able to withstand impacts without breaking suddenly. 
5. 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).
6. 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.
7. 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.
8. 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. 
9. 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:

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