Nickel alloys are nickel-based alloys (mixtures of nickel with other metals such as iron, copper, lead, etc.) which generally offer exceptional resistance to corrosion and high temperatures. These alloys are intended to improve certain specific properties of nickel that are of particular interest, depending on the intended use.
Properties of nickel alloys
Nickel alloys have a number of properties, such as:
- Electrical resistance
- Resistance to low and high temperatures
- Corrosion resistance, i.e. resistance to the formation of salts and insoluble metal hydroxides, as they slow down the rate of dissolution.
- Electronic and magnetic properties.
In these cases, a low level of impurities is always sought in order to minimise sensitivity to hot cracking and micro-cracking.
Most common nickel alloys
Nickel with copper
Nickel alloys with copper can be classified into different groups.
- First, there are the low nickel alloys, with a nickel content between 2 and 13%.
- Next, there are the cupro-nickels, with a nickel content between 10 and 13%.
- This is followed by coin alloys with 25% nickel.
- Those with 45% nickel are alloys with controlled electrical resistance.
- The so-called monel alloys have more than 50% nickel and a part of copper.
Nickel with iron
Depending on the amount of nickel they contain, they are also classified into different groups:
- Wrought steels: between 0.5 and 8% nickel.
- Magnetic alloys: 20 to 90% nickel.
- Non-magnetic alloys: 0.5 and 9% nickel.
- Stainless steel clad steels: 5 and 49% nickel.
- Iron-based superalloys: 0.2 - 9% nickel.
- Low coefficient: 36 and 50% nickel.
- Selected expansion: 22 and 50% nickel.
Nickel with chromium, iron and molybdenum
This group includes alloys with commercial names such as Inconel, Hastelloy, Udimet or Rene among others. They have been developed to withstand very corrosive environments. Most of the alloys in this group have excellent resistance to corrosion and oxidation.
Powder metallurgical nickel alloys
Powder metallurgical alloys are dispersion strengthened nickel-based and oxide dispersion strengthened alloys. They are created through proprietary powder metallurgy. The properties of these alloys are determined by the way they are processed.
Applications of nickel alloys
Nickel alloys are mainly used in the chemical, petrochemical, nuclear, naval, marine and aerospace industries. Nickel alloys have therefore become indispensable for the production of industrial components subjected to very demanding behaviour.
How to use the different types of nickel alloys
Their uses and applications will be differentiated mainly by their alloying elements.
- Pure nickel is generally used for caustic solutions.
- Nickel-copper alloy is used for milder reductant solutions, such as hydrofluoric acid.
- A nickel-molybdenum alloy will be used when working with strong reducing media.
- Nickel-iron-chromium alloy is the most suitable choice for oxidising solutions.
- For superoxidising media, a nickel-chromium-silicon alloy would be the best choice.
- Finally, the nickel-chromium-molybdenum alloy usually has sufficient versatility to cope with all these environments.
The use of copper, molybdenum or tungsten in a nickel alloy helps both to increase nickel's own inherent strength qualities and to significantly increase its strength. With respect to the use of chromium in nickel alloys, it helps to prevent the corrosion process, as it is involved in the formation of passive films. However, silicon is the best choice when there is a high potential for corrosion and these films cannot be maintained, as it protects the metal through the formation of protective oxides.
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