An alloy is a combination of a metal with one or more other metals or non-metals, such as carbon or phosphorus. An alloy may be a compound of the metals, a solid solution of them, a heterogeneous mixture, or any combination of these. The resultant physical properties differ from those of the components. Alloys are general harder and stronger, and have lower melting points, than their constituent elements. Combinations with the lowest melting point are called eutectic mixtures. In the table of alloys below, 26 elements are involved.

 

Alloys are useful because their properties can be adjusted as desired by varying the proportions of the constituents. Very few metals are used today in a pure state. Alloys are formed by mixing their molten components. The structures of alloys consisting mainly of one component may be substitutional or interstitial, depending on the relative sizes of the atoms. The study of alloy structures in general is complex.

 

The commonest alloys are the different forms of steel, which all contain a large proportion of iron and small amounts of carbon and other elements. Brass and bronze, two well-known and ancient metals, are alloys of copper, while pewter is an alloy of tin and lead. The very light but strong alloys used in aircraft construction are frequently alloys of aluminum and magnesium. Solders contain tin with lead and bismuth; type metal is an alloy of lead, tin, and some antimony. Among familiar alloys are those used in coins: modern "silver" coinage in most countries is an alloy of nickel and copper. Special alloys are used for such purposes as die-casting, dentistry, high-temperature applications, and for making thermocouples, magnets, and low-expansion materials.

 

A selection of alloys
Name	Composition expressed as percentages	Properties and uses
alnico	Fe 60, Ni 20, Al 10, Co 10	permanent magnet
Babbitt metal	Sn (predominates), Sb, Cu (+Pb)	used for bearings, anti-friction metal
brass	Cu with 20–35 Zn	decorative
bronze	Cu with 5–8 Sn	primitive tools, coinage
carboloy	W2C2 with 10 Cu	very hard alloy, grinding tools
cast iron	impure Fe, C up to 4½ with Mn, P, Si, and S traces	decorative work, weights
cupronickel	Cu 80, Ni 20 (coinage 25-75)	coinage
delta metal	Cu 55–60, Zn c. 40, Fe 2–4	bearings, marine propellers
dow metal	Al, Mg	aircraft and car parts
dental alloy	Ag, Cu, Zn, Sn	tooth fillings
duralumin	Al 93–95½, Cu 3½–5½, Mn ½–¾, Mg ½–¾	aircraft frames
Dutch metal	Cu with 30–35 Zn	bronze in gold leaf form
E-alloy	Al 78, Zn 20, Cu 2; Al 96, Zn 2, Cu 2	castings
electrum	Au with 15–45 Ag	coins (ancient times)
Frary metal	Pb 97, Ba 2, Ca 1	bearings
German metal	Cu 56–65, Zn 24–28, Ni 7–20	metal fittings, metal ware (often electroplated)
gun metal	Cu 88, Sn 8–10, Zn 2–4	ordnance
hiduminium	Al with small Cu, Ni, Mg, Si additions	aircraft parts
illium	complex of Co, Cr, Fe, Mn, Mb, Ni, and W	acid resistant
Jae metal	Ni 70, Cu 30	shunts on magnetic instruments
Lipowitz's alloy	Bi 50, Pb 27, Sn 13, Cd 10	very low melting point (60°C)
magnolia metal	Pb 80, Sb 15, Sn 5	medium duty bearings
monel metal	Ni 68, Cu 29½, Fe 1¼,	resistant to steam corrosion
Muntz metal, yellow metal	Cu 60, Zn 40	resistant to seawater corrosion
nichrome	Ni 60, Fe 20, Cr 20	filament wires
nickel silver	Cu 55–63, Ni 10–30, Zn 7–35	electroplated articles, hence E.P.N.S.
pewter	Sn 80, Pb 20, traces of Sb	modern pewter Pb replaced by Sb with some Cu and Bi
permalloy	Ni 77.5, Fe 22.5 (sometimes with traces of Co, Cr, Cu, and Mo)	magnetic properties, transformers, submarine cable parts
phosphorbronze	Cu 90, Sn 9½, P ½28	castings, bearings, and rsilient strip
pinchbeck	Cu 89–93, Zn 7–11	imitation gold, jewellery
"silver" alloy	Hg–Sn amalgam	"silver" backing for mirrors
solder	Sn½, Pb 33½	plumbing
speculum	Cu 60–70, Sn 30–40	high polish surfaces, plating
stainless steel	Fe 78–86, Cr 12–20, Ni 2	corrosion resistant culinary, sterile vessels, decorative
steel	essentially Fe with C ½–1½ with special purpose additices of Cr, Mn, Mb, Ni, Si, Al, Cu, Co, Ti, W, V	multifarious
stellite	Co 43, Cr 43, W 14 et al.	surgical and other cutting tools
tombac	Cu 71–90, Zn 10–29	cartridge cases
type metal	Pb 80–86, Sb 11–20, Sn 3–11	lino-, mono-, and stereotype fonts
white gold	Au with Ni	platinum substitute
Woods metal	Bi 50, Pb 25, Sn 12½, Cd 12½	low melting point, fire sprinklers
X-40	Co 55, Cr 25, Ni 9, W 7, C ½, Fe ½, traces of Mn, Si	non-creep at high temperatures, gas turbine rotor blades
Y-alloy	Al 93, Cu 4, Ni 2, Mn 1

 

Amalgam

An amalgam is an alloy of mercury with other metals. Most metals except iron and platinum will form amalgams; those with high mercury content are liquids, but most are solid. Amalgams of some noble metals occur naturally: silver and gold are extracted from their ores by forming amalgams. Dental amalgam, containing silver, copper, zinc, and tin, is used to fill teeth. Various amalgams may be used as electrodes.

 

Babbitt metal

Babbitt metal, also called bearing metal or simply Babbitt (and often spelled with a lowercase "b"), is an anti-friction alloy containing about 89% tin, 9% antimony, and 2% copper devised in 1839 by the American inventor Isaac Babbitt (1799–1862) for lining the bearings of steam engines. Various formulations have been devised but in most the microscopic structure consists of relatively hard crystals embedded in a soft matrix. Today the term Babbitt metal is applied to a variety of high-tin and high-lead bearing alloys.

 

Brass

Brass is a yellowish or reddish, malleable and ductile alloy of copper (55–95%) and zinc (5–45%), known since Roman times and widely used in industry and for ornament and decoration. Up to 36% zinc forms α-brass, which can be worked cold; with more zinc a mixture of α and β-brass is formed, which is less ductile but stronger. Brasses containing more than 45% zinc (white brasses) are unworkable and have few uses. Some brasses also contain other metals: lead to improve machinability, aluminum or tin for greater corrosion-resistance, and nickel, manganese, or iron for greater strength.

 

Brass is widely used for pipe and electrical fittings, screws, musical instruments, and ornamental metal work.

 

Britannia metal

Britannia metal is an alloy consisting of 5–10% antimony, about 1% copper, and the remainder tin. It resembles pewter, is lustrous, hard, and malleable, and is used as a base for electroplated silverware (see electroplating).

 

Bronze

Bronze is thought to have been the first metal alloy ever made, although it was probably produced originally by the accidental smelting of mixed ores of copper and tin. It is an alloy of copper and no more than 30% tin, known since the 4th millennium BC, and used then for tools and weapons, now for machine parts and marine hardware. Statues are often cast in bronze. It is a hard, strong alloy with good corrosion-resistance (the patina formed in air is protective). (Figures 2–4)

 

Various other components are added to bronze to improve hardness or machinability, such as aluminum, iron, lead, zinc, and phosphorus. Aluminum bronzes, and some others, contain no tin.

 

Electrum

Electrum is a pale yellow alloy of gold with up to 40% silver, occurring naturally as gold ore, and used for ornament. The term has been used for amber.

 

Gun metal

Gun metal is a type of wear-resistant bronze, normally 88% copper, 10% tin, and 2% zinc. Formerly used to make heavy field and naval guns, it is now used for gears, bearings, and steam fittings, being wear- and corrosion-resistant.

 

Misch metal

Misch metal is an alloy composed of 50% cerium, 25% lanthanum, 15% neodymium, 10% other rare earths, and iron. It is used to make 'flints' for cigarette lighters and as a deoxidizer for vacuum tubes.

 

Monel metal

Monel metal is a strong, corrosion-resistant alloy composed of 68% nickel, 29% copper, and 3% iron, manganese, silicon, and carbon. It is used for turbine blades, propellers, etc. Originally, monel metal was made by smelting nickel/copper ore from Sudbury, Ontario.

 

Nickel silver

Nickel silver, also called German silver, is an alloy of copper, nickel, and zinc. Nickel silver is hard and does not tarnish easily. It resembles silver, and is used for cheap jewelry, cutlery, etc., and as the base for silver-plated ware (E.P.N.S., electroplated nickel silver).

 

Permalloy

Permalloy is an alloy of iron and nickel, often with 5% molybdenum. It has a very high magnetic permeability and is used in transformers.

 

Pewter

Pewter is a class of silver-colored, soft alloys consisting chiefly of tin, now hardened with copper and antimony, and usually containing lead. Roman pewter was high in lead and darkened with age. Pewter has been used for bowls, drinking vessels, and candlesticks.

 

The most common form has about four parts of tin to one of lead, combined with small amounts of antimony and copper. Some food and drink can become contaminated with poisonous lead from pewter utensils, so other alloys have replaced pewter for such items.

 

Pinchbeck

Pinchbeck is an alloy of copper and zinc but with much less zinc than is contained in brass. Invented by the London watchmaker Christopher Pinchbeck (c. 1670–1732), it is used to simulate gold.

 

Speculum

Speculum is a brittle white alloy of two parts copper to one part tin that takes a very high polish and was used for telescope mirrors until the late nineteenth century. The manufacture of speculum mirrors reached its apex with William Parsons, third Earl of Rosse, who managed to produce several 36-inch (91-centimeter) Newtonians and later, in 1845, a colossus 72 inches (1.8 meters) in diameter. However, speculum, which is difficult to work with and quick to tarnish (forcing a repolishing of the optical surface itself) was made obsolete in astronomy with the development of silvering and aluminizing.

 

Type metal

Type metal is any of various alloys of lead, antimony, and tin, easily cast to make printing type. Owing to the presence of antimony, type metal expands on solidifying and thus gives a sharp cast. Type metal contains 2.5–25% lead and 2.5–25% antimony; both tin and antimony lower the melting point, which is usually between 240° and 250°C (460–475°F).

 

 

Superalloys

So-called superalloys are alloys of cobalt and nickel used as surface materials for spacecraft to withstand the rapid heating and high temperatures caused by the passage through the Earth's atmosphere particularly on re-entry from space. These alloys oxidize in air above 700 °C (1,300 °F) but the oxide coating initially formed prevents further oxidation.