In general, nickel alloys can be divided into the following two categories: nickel-copper alloys and nickel-chromium base alloys.
Nickel-copper alloys are also known as Monel alloys. In addition to nickel, they contain 29-33% copper as well as small amounts of iron and manganese. The main properties of nickel-copper alloys include high corrosion resistance, great mechanical strength, good ductility and a low coefficient of thermal expansion. However, they do tend to quickly work-harden.
In general, nickel-copper alloys are used where a higher strength is required compared to pure nickel. Because of their superb resistance to acids and alkalis, they are frequently used in chemical plant equipment. With small additions of aluminum and titanium, Monel alloys can also be used in the aerospace industry. Other common applications include valve stems, heat exchangers, screw machine products, piping systems, fuel and water tanks, kitchen sinks and more.
2. Nickel-chromium base alloys
Nickel-chromium alloys provide resistance to oxidation and metal failure through a loss of strength that often occurs at high temperatures (with the exception of high-temperature sulfur-rich environments). Thanks to their excellent resistance to acid, alkalis, water and seawater, oxidation, flammability, and organic solvents, nickel-chromium alloys are usually applied where particular heat and corrosion resistance is required.
Nickel-chromium alloys can be divided into two categories:
1. The first group includes cast alloys that contain 40-50% nickel and 50-60% chrome. These alloys are heat and corrosion resistant. Their applications include structural parts, containers, supports, hangers, spacers etc. that are exposed to temperatures up to 1994 °F (1090 °C).
2. The other group of nickel-chromium alloys contains significantly more nickel (70-80%). Their applications include resistance heating elements exposed to temperatures up to 2102°F (1150 °C).
The more recent nickel-chromium base alloys contain a variety of ancillary elements, the addition of which creates new and improved alloy properties.
Low expansion and magnetic alloys
Two particular nickel group alloys that exhibit distinctive properties are low expansion alloys and magnetic alloys.
Low expansion alloys are nickel-iron alloys exhibit low and constant expansion coefficient over a particular temperature range. They are used in medical, scientific and automotive industries to manufacture precision instruments, scientific instruments, laboratory devices, motor valves, aircraft industry parts and electronic parts.
Magnetic alloys are complex alloys. The high-nickel magnetic alloys exhibit high initial permeability and fairly low saturation induction while soft magnetic nickel-iron alloys are used in switchgear and for direct current motors and generators.