What is a nickel-based alloy?

About Nickel-based Alloys

Nickel-based alloys are also referred to as ni-based superalloys due to their outstanding strength, heat resistance and corrosion resistance. The face-centered crystal structure is a distinctive feature of ni-based alloys, since nickel operates as a stabilizer for the austenite.

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Common additional chemical elements to nickel-based alloys are chromium, cobalt, molybdenum, iron and tungsten.

Inconel® and Hastelloy® Nickel-based Alloys

Two of the most established nickel-based alloys families are Inconel® and Hastelloy®. Other notable manufacturers are Waspaloy®, Allvac® and General Electric®.

The most common Inconel® nickel-based alloys are:

• Inconel® 600, 2. (72% Ni, 14-17% Cr, 6-10% Fe, 1% Mn, 0.5%Cu): A nickel-chrome-iron alloy that displays excellent stability on a broad temperature scale. Stable against chlorine and chlorine water.
• Inconel® 617, 2. (Nickel balance, 20-23% Cr, 2% Fe, 10-13%Co, 8-10% Mo, 1.5% Al, 0.7% Mn, 0.7 % Si): This alloy made largely of nickel, chrome, cobalt and molybdenum displays high strength and heat resistance.
• Inconel® 718 2. (50-55% Ni, 17-21% Cr, iron balance, 4.75-5.5% Nb, 2.8-3.3% Mo, 1%Co, ): A hardenable nickel-chrome-iron-molybdenum alloy that is known for its good workability and excellent mechanical properties at low temperatures.

Hastelloy® nickel-based alloys are known for their resistance against acids. The most common ones are:

• Hastelloy® C-4, 2. (Nickel balance, 14.5 &#; 17.5% Cr, 0 &#; 2% Co, 14 &#; 17% Mo, 0 &#; 3% Fe, 0 &#; 1% Mn): C-4 is a nickel-chrome-molybdenum alloy that is applied in environments with inorganic acids.
• Hastelloy® C-22, 2. (Nickel balance, 20 -22.5% Cr, 0 &#; 2.5% Co, 12.5 &#; 14.5% Mo, 0 &#; 3% Fe, 0-0.5% Mn, 2.5 -3.5 W): C-22 is a corrosion-resistant nickel-chrome-molybdenum-tungsten alloy that displays good persistence against acids.
• Hastelloy® C-, 2. (Nickel balance, 23% Cr, 2% Co, 16% Mo, 3% Fe): C- is used in environments with aggressive oxidants, such as sulfuric acid and ferric chloride.

Improving durability of nickel-based work pieces

Nickel-based alloys are known for their excellent mechanical properties, such as corrosion resistance and high temperature stability. However, almost no work piece can last forever, no matter how splendid the material. To prolong lifespan of parts, nickel based alloys can be treated with BoroCoat®, our diffusion treatment to significantly improve corrosion and wear resistance as well as provide stability against oxidants.

The diffusion layers of BoroCoat® improve surface hardness to up to HV while maintaining a diffusion layer of 60 µm. The wear resistance is considerably improved, as is proven by the pin on disc test. While the wear depth of untreated nickel-based alloys increases the longer the pin rotates, ni-based alloys with BoroCoat® display consistent low wear depth throughout the test.

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Areas of Application

Alloys with a nickel basis are often used in challenging environments that demand good resistance against high and low temperatures, oxidation/corrosion and high strength. This is why applications include but are not limited to: turbine engineering, power plant technology, chemical industry, aerospace engineering and valves/fittings.

Not all metals can be mixed with nickel, but some of the most common elements are iron, chromium, aluminum, molybdenum, copper, cobalt, and titanium. To make nickel alloys, you&#;d have to follow the same process used for pretty much every other metal alloy. The alloying elements need to be decided on, and their ratios need to be carefully chosen. Once that&#;s done, the elements are all melted together in something like an arc furnace, which also purifies them, and then the alloy is cast into ingots, and off to be formed using either cold or hot processing.

A Brief History

It&#;s believed that the first nickel alloy was used in 200 BCE in China. That&#;s the earliest record available, and the material was referred to as &#;white copper,&#; which experts believe was an alloy of nickel and silver. Fast forward to , A. F. Cronstedt, a German scientist, managed to isolate nickel from the niccolite mineral. Copper and zinc were often found in these first nickel alloys, which came to be known as &#;German silver&#; and weren&#;t really used for anything other than ornaments.

After James Riley made an iron-chromium alloy in , W. H. Hatfield figured out that adding nickel to these alloys would make them incredibly corrosion-resistant. This led to the creation of what we now know as austenitic stainless steel.

Nickel Alloy Characteristics

Here are the main characteristics of nickel alloys:

• Corrosion/oxidation resistant
• High strength
• Heat resistance up to 980°C
• Highly ductile, won&#;t break easily if bent
• Magnetic, can easily be magnetized and demagnetized
• Weldability with various welding methods (although could develop hot or warm cracking and porosity)
• Low thermal conductivity, higher with nickel-copper alloys
• Low electrical conductivity, less than pure copper or silver
• Low thermal expansion coefficient, great for precision
• Varying colors depending on alloying element

It&#;s generally quite hard to differentiate nickel alloys from other types of metals. Nickel alloys can seem slightly dull when their surface is rough, but when it&#;s smooth, they can be shiny and reflective. Here&#;s an example of what copper-nickel alloy rods look like:

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