Why is Nickel Used in Alloys?

Nickel is one of the most commonly used alloying elements, being added to hundreds of different types and grades of materials, from Stainless steel to high-performance aerospace alloys used in turbine engines.

One of the main reasons Nickel is used as an alloying element is for its ability to increase strength and corrosion resistance, particularly in high-temperature applications. Nickel also readily alloys with other elements such as Chromium, Molybdenum and Iron, making the production of said alloys more successful.

What do Nickel alloys look like?

Whilst the alloying elements greatly affect the properties of Nickel alloys, the appearance is generally the same, with a lustrous (shiny) white/gray surface.

A good way to identify most Nickel alloys is to check the color and shape of the sparks when ground with a high-speed grinding wheel. Nickel and its alloys produce few, short orange sparks. This is in contrast to Iron alloys that produce lots of log orange sparks.

What types of Nickel alloys are available?

Because Nickel is so prominent as an alloying element, there are hundreds of different Nickel alloy products.

Wrought Nickel

Wrought or pure nickel is often utilized for its excellent corrosion resistance, particularly against caustic substances. It is also used for producing electrical components, often stamped from strip material.

Wrought Nickel Characteristics

Strength and Ductility – Wrought Nickel has relatively low strength compared to some nickel alloys, but good ductility. Weldability is good, with many compatible consumables available commercially. Wrought Nickel has excellent corrosion resistance and is often used for its resistance to caustic corrosion even at high temperatures.

Nickel-Iron Alloys

The principle uses of Nickel-Iron alloys exploit the material’s extremely low coefficient of thermal expansion. This makes it ideal for scientific instruments that rely on accurate dimensional tolerance across a wide temperature range.

Nickel-Iron Characteristics

Nickel-iron alloys are typically very soft and malleable, making them ideal for use as seals in metal-to-glass applications. Another revered characteristic is its magnetic properties, giving rise to its use in transformers, amplifiers and more.

Nickel-Copper Alloys (Inconel)

Nickel Copper alloys offer excellent resistance to alkaline solutions and seawater. Common uses include brine processing equipment or allied applications in the food industry.

Nickel-Copper Characteristics

Inconel is capable of being fabricated and welded to produce strong and durable components. It exhibits no ductile to brittle transition, meaning it retains its strength well into cryogenic temperatures.

One of the most commonly used Nickel-copper alloys is Inconel 400, a versatile alloy that is available in all common shapes and sizes such as bar, sheet, section and tube. This material is also readily forged and cast, allowing for extremely complex parts to be manufactured.

It finds perfect applications in valve bodies, hydraulic tubing, and firewater systems.

Nickel-Molybdenum Alloys (Hastelloy)

These alloys are primarily used for components that are resistant to ferric and cupric acids. Despite containing 26-30% molybdenum, they are available in many different shapes for fabricating into complex components.

Nickel-Molybdenum Characteristics

One of the most common Nickel-Molybdenum alloys is Hastelloy B-2. It is capable of resisting pure sulphuric and phosphoric acids, whilst being very weldable and easy to fabricate with. Nickel-molybdenum alloys also have a low thermal expansion coefficient and low-temperature performance.

Nickel-Chromium Alloys

With extremely high-temperature resistance, Nickel-chromium alloys are found in aerospace engineering and similar industries, where creep resistance is paramount. They are often work-hardenable, making them more versatile for high-strength applications that also require complex shapes and manufacturing processes.

Nickel-chromium Characteristics

Strength at extremely high temperatures is the main characteristic of Nickel-chromium alloys, with creep resistance being an allied benefit. Whilst weldability is not as high as other materials we’ve discussed, the material can be used to make complex shapes using other processes. Its corrosion and oxidation resistance is excellent and aids its use in aerospace turbine engine applications.

Nickel-Chromium-Iron Alloys

Some alloys previously considered Nickel-chromium-iron, have been reclassified as Stainless steels due to their high Iron content, but there are still alloys such as 825 and G-3 that are NI-Cr-Fe materials. The latter, also containing copper, has many applications concerning flue gas desulfurization systems.

Nickel-Chromium-Iron Characteristics

Good weldability allows this material to be used in the fabrication of complex shapes, pipework and process equipment. Its good resistance to phosphoric and sulphuric acids lends itself to the aforementioned gas desulfurization systems, also known as scrubbers. Its coefficient of expansion is low, and mechanical properties such as strength and relative hardness are high.

Nickel-Chromium-Cobalt Alloys

Adding Cobalt to Ni-Cr alloys significantly aids rupture and creep strength. The Cobalt atoms achieve this by enabling solid-solution strengthening of the material. As it has significantly improved creep resistance, NI-Cr-Co alloys are perfect for high-temperature applications.

Nickel-Chromium-Cobalt Characteristics

Alongside improved strength and creep resistance, alloys such as HR-160 have very high resistance to sulfidizing environments, even at high temperatures. Weldability is good, with many filler materials being commercially available.

Nickel-Chromium-Molybdenum Alloys

Alloy C-276 is the most widely used Ni-Cr-Mo alloy, the main plus point of this material being its excellent resistance to reducing acids such as hydrochloric and sulphuric. Alloy C-276 is commonly used to make pressure vessels, scrubbers and reactor vessels.

Nickel–Chromium-Molybdenum Characteristics

This alloy, like most Nickel-Chromium alloys, has very good high-temperature corrosion resistance, particularly against reducing acids. It has reasonably high strength, and high weldability, allowing it to be fabricated into complex shapes and assemblies.

Conclusion

Nickel is an incredibly useful material in industrial processes. Whilst it is generally too expensive to use for anything outside of its tailored use cases, its properties ranging from high and low-temperature corrosion resistance and strength to high weldability, make it perfect for processing industries involving caustic, acidic or other corrosive substances.