The metal and its alloys

Nickel plating

Nickel is resistant to corrosion by fluorine, alkalies, and a variety of organic materials. It remains bright on indoor exposure but tarnishes outdoors, although its corrosion rate is very low. Its low corrosion rate, coupled with its resistance to corrosion by sodium chloride and other chlorides used on roads during the winter, makes it essential as an undercoat on chromium-plated automotive trim. Heavy nickel plating is employed as a lining for tank cars and as a coating for the inner walls of large pipes and similar equipment in the chemical industry.

Copper-nickel

The addition of copper to nickel provides a series of useful alloys. Monel metal, 67 percent nickel and the balance essentially copper, is stronger than nickel and has broad corrosion-resisting applications. Extremely resistant to rapidly flowing seawater, it has many marine uses. The addition of a small percentage of aluminum and titanium renders it precipitation-hardenable; this high-strength version is widely used for propeller shafts. Increasing copper to 55 percent produces the electrical resistance alloy known as constantan, which is used as a thermocouple in conjunction with pure copper.

The 30 percent and 10 percent nickel-copper alloys, usually containing 0.5 percent and 1.5 percent iron, are widely used in the form of tubes for heat interchangers and condensers. Their resistance to seawater corrosion makes them important in desalination plants. Copper-based alloys containing a small percentage of nickel become precipitation-hardenable if 5–8 percent tin or a smaller amount of silicon or phosphorus is added. These have special uses.

The ancient Chinese alloy pai-t’ung, now known as nickel-silver, contains 10–30 percent nickel with the balance copper plus zinc. This alloy continues as a favoured base for silver-plated ware. It also is used as a spring material for relays and has numerous other applications.

An alloy of 25 percent nickel and 75 percent copper, essentially white in colour, was adopted for coinage by Belgium in 1860 and by the United States five years later. More recently it has been employed as the outer layer of copper-centred coins. Pure nickel was adopted by the Swiss for coinage in 1881; this use has spread to many other countries.

Magnetic alloys

The fact that nickel changes in length as it is magnetized makes it useful as an ultrasonic transducer in various underwater defense devices. Alloying nickel with about 21 percent iron has a spectacular effect in producing alloys with extraordinarily high magnetic permeability in weak fields. This type of alloy, known as Permalloy, discovered at Bell Telephone Laboratories in 1916, has had a great value in long-distance telephone transmission, including undersea cables. Other alloys of about 45–50 percent nickel and the balance iron, have been developed for magnetic uses at higher field strengths.

A remarkable group of nickel-containing permanent-magnet alloys was developed beginning in Japan in the early 1930s. An early example contained 25 percent nickel, 12 percent aluminum, and the balance iron. More powerful versions, such as Alnico V (containing 8 percent aluminum, 14 percent nickel, 24 percent cobalt, 3 percent copper, balance iron), developed in the Netherlands, were heat-treated in a magnetic field. These materials had a profound effect on the design of many electrical devices, including magnetic separators, DC motors, and automobile generators.

Thermal-expansion alloys

Invar, an alloy containing 36 percent nickel, with the balance iron, is notable for its extremely small thermal expansion. Discovered in 1898, it has, along with later-developed nickel alloys, many applications ranging from thermostats to balance wheels for watches, metal-to-glass seals essential to electric lights, and radio tubes.

High-strength steels

The first major market for nickel was in the production of nickel and nickel-chromium steels for armour plate, an application based on the work of James Riley of Glasgow, Scot., in 1889 and tests by the U.S. Navy in 1891 on armour plate from a French steel producer. Military demands supported the industry for many years, but, with the development of steam-turbine power plants, the automobile, agricultural machines, and aircraft, a whole new group of high-strength steels containing from 0.5 to about 5 percent nickel along with other metals such as chromium and molybdenum were developed. More recently, with a demand for steels for ultralow-temperature use with liquefied gases, steel of 9 percent nickel and alloys of higher nickel content have come into demand. These steels rely on carbon for hardening by heat treatment. The nickel toughens the steel and slows the hardening process so that larger sections can be heat-treated. A carbon-free iron alloy known as maraging steel has been developed. It contains 18 percent nickel, plus cobalt, titanium, and molybdenum. This alloy can be heat-treated to provide a tensile strength of some 2,000 megapascals (i.e., 21,000 kilograms per square centimetre, or 300,000 pounds per square inch), coupled with an elongation of 5 to 10 percent.