An intermetallic (also called intermetallic compound, intermetallic alloy, ordered intermetallic alloy, long-range-ordered alloy) is a type of metallic

alloy An alloy is a mixture of chemical elements of which in most cases at least one is a metal, metallic element, although it is also sometimes used for mixtures of elements; herein only metallic alloys are described. Metallic alloys often have prop ...

that forms an ordered solid-state compound between two or more metallic elements. Intermetallics are generally hard and brittle, with good high-temperature mechanical properties. They can be classified as

stoichiometric Stoichiometry () is the relationships between the masses of reactants and products before, during, and following chemical reactions. Stoichiometry is based on the law of conservation of mass; the total mass of reactants must equal the total m ...

or nonstoichiometic. The term "intermetallic compounds" applied to solid phases has long been in use. However, Hume-Rothery argued that it misleads, suggesting a fixed stoichiometry and a clear decomposition into

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

Definitions

Research definition

In 1967 defined intermetallic compounds as ''solid phases containing two or more metallic elements, with optionally one or more non-metallic elements, whose crystal structure differs from that of the other constituents''. This definition includes: * Electron (or Hume-Rothery) compounds * Size packing phases. e.g. Laves phases, Frank–Kasper phases and Nowotny phases * Zintl phases The definition of metal includes: *

Post-transition metal The metallic elements in the periodic table located between the transition metals to their left and the chemically weak nonmetallic metalloids to their right have received many names in the literature, such as post-transition metals, poor metal ...

s, i.e.

aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

gallium Gallium is a chemical element; it has Chemical symbol, symbol Ga and atomic number 31. Discovered by the French chemist Paul-Émile Lecoq de Boisbaudran in 1875, elemental gallium is a soft, silvery metal at standard temperature and pressure. ...

indium Indium is a chemical element; it has Symbol (chemistry), symbol In and atomic number 49. It is a silvery-white post-transition metal and one of the softest elements. Chemically, indium is similar to gallium and thallium, and its properties are la ...

thallium Thallium is a chemical element; it has Symbol (chemistry), symbol Tl and atomic number 81. It is a silvery-white post-transition metal that is not found free in nature. When isolated, thallium resembles tin, but discolors when exposed to air. Che ...

, tin,

lead Lead () is a chemical element; it has Chemical symbol, symbol Pb (from Latin ) and atomic number 82. It is a Heavy metal (elements), heavy metal that is density, denser than most common materials. Lead is Mohs scale, soft and Ductility, malleabl ...

, and

bismuth Bismuth is a chemical element; it has symbol Bi and atomic number 83. It is a post-transition metal and one of the pnictogens, with chemical properties resembling its lighter group 15 siblings arsenic and antimony. Elemental bismuth occurs nat ...

. *

Metalloid A metalloid is a chemical element which has a preponderance of material property, properties in between, or that are a mixture of, those of metals and Nonmetal (chemistry), nonmetals. The word metalloid comes from the Latin language, Latin ''meta ...

s, e.g.

silicon Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...

germanium Germanium is a chemical element; it has Symbol (chemistry), symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid or a nonmetal in the carbon group that is chemically ...

arsenic Arsenic is a chemical element; it has Symbol (chemistry), symbol As and atomic number 33. It is a metalloid and one of the pnictogens, and therefore shares many properties with its group 15 neighbors phosphorus and antimony. Arsenic is not ...

antimony Antimony is a chemical element; it has chemical symbol, symbol Sb () and atomic number 51. A lustrous grey metal or metalloid, it is found in nature mainly as the sulfide mineral stibnite (). Antimony compounds have been known since ancient t ...

and

tellurium Tellurium is a chemical element; it has symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur, all three of which are chalcogens. It is occasionally fou ...

. Homogeneous and heterogeneous

solid solution A solid solution, a term popularly used for metals, is a homogeneous mixture of two compounds in solid state and having a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The word "solutio ...

s of metals, and interstitial compounds such as

carbide In chemistry, a carbide usually describes a compound composed of carbon and a metal. In metallurgy, carbiding or carburizing is the process for producing carbide coatings on a metal piece. Interstitial / Metallic carbides The carbides of th ...

s and

nitride In chemistry, a nitride is a chemical compound of nitrogen. Nitrides can be inorganic or organic, ionic or covalent. The nitride anion, N3−, is very elusive but compounds of nitride are numerous, although rarely naturally occurring. Some nitr ...

s are excluded under this definition. However, interstitial intermetallic compounds are included, as are alloys of intermetallic compounds with a metal.

Common use

In common use, the research definition, including

post-transition metal The metallic elements in the periodic table located between the transition metals to their left and the chemically weak nonmetallic metalloids to their right have received many names in the literature, such as post-transition metals, poor metal ...

s and

metalloid A metalloid is a chemical element which has a preponderance of material property, properties in between, or that are a mixture of, those of metals and Nonmetal (chemistry), nonmetals. The word metalloid comes from the Latin language, Latin ''meta ...

s, is extended to include compounds such as

cementite Cementite (or iron carbide) is a compound of iron and carbon, more precisely an intermediate transition metal carbide with the formula Fe3C. By weight, it is 6.67% carbon and 93.3% iron. It has an orthorhombic crystal structure. It is a hard, b ...

, Fe₃C. These compounds, sometimes termed interstitial compounds, can be

, and share properties with the above intermetallic compounds.

Complexes

The term intermetallic is used to describe compounds involving two or more metals such as the cyclopentadienyl complex Cp₆Ni₂Zn₄.

B2

A B2 intermetallic compound has equal numbers of atoms of two metals such as aluminum and iron, arranged as two interpenetrating simple cubic lattices of the component metals.

Properties

Intermetallic compounds are generally brittle at room temperature and have high melting points. Cleavage or intergranular fracture modes are typical of intermetallics due to limited independent slip systems required for plastic deformation. However, some intermetallics have ductile fracture modes such as Nb–15Al–40Ti. Others can exhibit improved

ductility Ductility refers to the ability of a material to sustain significant plastic Deformation (engineering), deformation before fracture. Plastic deformation is the permanent distortion of a material under applied stress, as opposed to elastic def ...

by alloying with other elements to increase grain boundary cohesion. Alloying of other materials such as

boron Boron is a chemical element; it has symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the boron group it has three ...

to improve grain boundary cohesion can improve ductility. They may offer a compromise between

ceramic A ceramic is any of the various hard, brittle, heat-resistant, and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcela ...

and metallic properties when hardness and/or resistance to high temperatures is important enough to sacrifice some

toughness In materials science and metallurgy, toughness is the ability of a material to absorb energy and plastically deform without fracturing.magnetic Magnetism is the class of physical attributes that occur through a magnetic field, which allows objects to attract or repel each other. Because both electric currents and magnetic moments of elementary particles give rise to a magnetic field, m ...

and chemical properties, due to their strong internal order and mixed ( metallic and

covalent A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atom ...

/ ionic) bonding, respectively. Intermetallics have given rise to various novel materials developments.

Applications

Examples include alnico and the hydrogen storage materials in nickel metal hydride batteries. Ni₃Al, which is the hardening phase in the familiar nickel-base super alloys, and the various

titanium Titanium is a chemical element; it has symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...

aluminides have attracted interest for

turbine blade ...

applications, while the latter is also used in small quantities for grain refinement of titanium alloys.

Silicide A silicide is a type of chemical compound that combines silicon and a usually more electropositive element. Silicon is more electropositive than carbon. In terms of their physical properties, silicides are structurally closer to borides than t ...

s, intermetallics involving silicon, serve as barrier and contact layers in

microelectronics Microelectronics is a subfield of electronics. As the name suggests, microelectronics relates to the study and manufacture (or microfabrication) of very small electronic designs and components. Usually, but not always, this means micrometre ...

. Others include: * Magnetic materials e.g. alnico, sendust, Permendur, FeCo, Terfenol-D *

Superconductors Superconductivity is a set of physical properties observed in superconductors: materials where electrical resistance vanishes and magnetic fields are expelled from the material. Unlike an ordinary metallic conductor, whose resistance decreases ...

e.g. A15 phases, niobium-tin * Hydrogen storage e.g. AB₅ compounds ( nickel metal hydride batteries) * Shape memory alloys e.g. Cu-Al-Ni (alloys of Cu₃Al and nickel),

Nitinol Nickel titanium, also known as nitinol, is a metal alloy of nickel and titanium, where the two elements are present in roughly equal atomic percentages. Different alloys are named according to the weight percentage of nickel; e.g., nitinol 55 and ...

(NiTi) * Coating materials e.g. NiAl * High-temperature structural materials e.g. nickel aluminide, Ni₃Al * Dental amalgams, which are alloys of intermetallics Ag₃Sn and Cu₃Sn * Gate contact/ barrier layer for

e.g. TiSi₂ * Laves phases (AB₂), e.g., MgCu₂, MgZn₂ and MgNi₂. The unintended formation of intermetallics can cause problems. For example, intermetallics of gold and aluminium can be a significant cause of wire bond failures in

semiconductor device A semiconductor device is an electronic component that relies on the electronic properties of a semiconductor material (primarily silicon, germanium, and gallium arsenide, as well as organic semiconductors) for its function. Its conductivit ...

s and other

devices. The management of intermetallics is a major issue in the reliability of

solder Solder (; North American English, NA: ) is a fusible alloy, fusible metal alloy used to create a permanent bond between metal workpieces. Solder is melted in order to wet the parts of the joint, where it adheres to and connects the pieces aft ...

joints between electronic components.

Intermetallic particles

Intermetallic particles often form during solidification of metallic alloys, and can be used as a dispersion strengthening mechanism.

History

Examples of intermetallics through history include: * Roman yellow

brass Brass is an alloy of copper and zinc, in proportions which can be varied to achieve different colours and mechanical, electrical, acoustic and chemical properties, but copper typically has the larger proportion, generally copper and zinc. I ...

, CuZn * Chinese high tin

bronze Bronze is an alloy consisting primarily of copper, commonly with about 12–12.5% tin and often with the addition of other metals (including aluminium, manganese, nickel, or zinc) and sometimes non-metals (such as phosphorus) or metalloid ...

, Cu₃₁Sn₈ *

Type metal In printing, type metal refers to the metal alloys used in traditional Movable type, typefounding and hot metal typesetting. Historically, type metal was an alloy of lead, tin and antimony in different proportions depending on the application, b ...

, SbSn * Chinese white copper, CuNi German type metal is described as breaking like glass, without bending, softer than copper, but more fusible than lead. The chemical formula does not agree with the one above; however, the properties match with an intermetallic compound or an alloy of one.

Definitions

Research definition

Common use

Complexes

B2

Properties

Applications

Intermetallic particles

History

See also

References

Sources

External links