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Nickel Alloys

Nickel in elemental form or alloyed with other metals and materials has made significant contributions to our present-day society and promises to continue to supply materials for an even more demanding future. Nickel has always been a vital metal for a wide variety of industries for the simple reason that it is a highly versatile material that will alloy with most other metals.

Nickel is a versatile element and will alloy with most metals. Nickel alloys are alloys with nickel as principal element. Complete solid solubility exists between nickel and copper. Wide solubility ranges between iron, chromium, and nickel make possible many alloy combinations. Its high versatility, combined with its outstanding heat and corrosion resistance has led to its use in a diverse range of applications; such as Aircraft gas turbines, steam turbines in power plants and its extensive use in the energy and nuclear power markets.

Iron-Nickel-Chromium Alloys

This series of alloys has also found extensive use in the high-temperature petrochemical environments, where sulfur-containing feedstocks (naphtha and heavy oils) are cracked into component distillate parts. Not only were they resistant to chloride-ion stress-corrosion cracking, but they also offered resistance to polythionic acid cracking. Some alloys of commercial importance include:

1- Alloy 800 (Fe-32Ni-21Cr): The basic alloy in the Fe-Ni-Cr system; resistant to oxidation and carburization at elevated temperatures

2- Alloy 800HT: Similar to 800H with further modification to combined titanium and aluminum levels (0.85 to 1.2%) to ensure optimum high-temperature properties

3- Alloy 801: Increased titanium content (0.75 to 1.5%); exceptional resistance to polythionic acid cracking

4- Alloy 802: High-carbon version (0.2 to 0.5%) for improved strength at high temperatures

5- Alloy 825 (Fe-42Ni-21.5Cr-2Cu): Stabilized with titanium addition (0.6 to 1.2%). Also contains molybdenum (3%) for pitting resistance in aqueous corrosion applications. Copper content bestows resistance to sulfuric acid

6- Alloy 925: Addition of titanium and aluminum to 825 composition for strengthening through age hardening

The 800 alloy series

The 800 alloy series offers excellent strength at elevated temperature (creep and stress rupture).

Some corrosion variants in the Fe-Ni-Cr system include:

1- 20Cb3 (Fe-35Ni-20Cr-3.5Cu-2.5Mo + Nb):

This alloy was developed for the handling of sulfuric acid environments

2- 20Mo-4 and 20Mo-6 (Fe-36Ni-23Cr-5Mo + Cu):

Increased corrosion resistance in pulp and paper industry environments.

Nickel-lron Low-Expansion Alloys

This series of alloys plays a very important role in both the lamp industry and electronics, where glass-to-metal seals in encapsulated components are important. The nickel alloys are chosen for a variety of reasons.

Some alloys of commercial importance include:

1- Invar (Fe-36Ni): This alloy has the lowest thermal expansion of any metal from ambient to 230°C (450°F)

2- Alloy 42 (Fe-42Ni): This alloy has the closest thermal expansion match to alumina, beryllia, and vitreous glass

Alloy 426. Additions of 6% Cr are added to this alloy for vacuum-tight sealing applications

Alloy 52 (Fe-51.5Ni). This alloy has a thermal expansion that closely matches vitreous potash-soda-lead glass.