Anintermetallic is a type ofmetallicalloy that forms an ordered solid-statecompound between two or more metallic elements. Alternatively, it can be calledintermetallic compound,intermetallic alloy,ordered intermetallic alloy, orlong-range-ordered alloy. Intermetallics are generally hard and brittle, with good high-temperature mechanical properties.[1][2][3] They can be classified asstoichiometric ornonstoichiometic.[1]
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 intospecies.[4]
In 1967Gustav Ernst Robert Schulze [de] defined intermetallic compounds assolid 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.[5] This definition includes:
The definition of metal includes:[citation needed]
Homogeneous and heterogeneoussolid solutions of metals, andinterstitial compounds such ascarbides andnitrides are excluded under this definition. However, interstitial intermetallic compounds are included, as are alloys of intermetallic compounds with a metal.[citation needed]
In common use, the research definition, includingpost-transition metals andmetalloids, is extended to include compounds such ascementite, Fe3C. These compounds, sometimes termedinterstitial compounds, can bestoichiometric, and share properties with the above intermetallic compounds.[citation needed]
The term intermetallic is used[7] to describe compounds involving two or more metals such as thecyclopentadienyl complex Cp6Ni2Zn4.
.png)
AB2 (also known as cesium chloride structure type) intermetallic compound has equal numbers of atoms of two metals, such as aluminium-iron, andaluminium-nickel, arranged as two interpenetrating simple cubic lattices of the component metals.[8]
Intermetallic compounds are generally brittle at room temperature and have highmelting point, though many also exhibit metallic conductivity or semiconducting behavior depending on the degree of covalent bonding. Cleavage or intergranular fracture modes are typical of intermetallics due to limited independentslip systems required for plastic deformation. However, some intermetallics have ductile fracture modes such as Nb–15Al–40Ti. Others can exhibit improvedductility by alloying with other elements to increase grain boundary cohesion. Alloying of other materials such asboron to improve grain boundary cohesion can improve ductility.[9] They may offer a compromise betweenceramic and metallic properties when hardness and/or resistance to high temperatures is important enough to sacrifice sometoughness and ease of processing. They can display desirablemagnetic and chemical properties, due to their strong internal order and mixed (metallic andcovalent/ionic) bonding, respectively. Intermetallics have given rise to various novel materials developments.[citation needed]
| Intermetallic Compound | Melting Temperature (°C) | Density (kg/m3) | Young's Modulus (GPa) |
|---|---|---|---|
| FeAl | 1250–1400 | 5600 | 263 |
| Ti3Al | 1600 | 4200 | 210 |
| MoSi2 | 2020 | 6310 | 430 |
Examples includealnico and thehydrogen storage materials innickel metal hydride batteries.Ni3Al, which is the hardening phase in the familiar nickel-basesuper alloys, and the varioustitanium aluminides have attracted interest forturbine blade applications, while the latter is also used in small quantities forgrain refinement oftitanium alloys.Silicides, intermetallics involving silicon, serve as barrier and contact layers inmicroelectronics.[10] Others include:
The unintended formation of intermetallics can cause problems. For example,intermetallics of gold and aluminium can be a significant cause ofwire bond failures insemiconductor devices and othermicroelectronics devices. The management of intermetallics is a major issue in the reliability ofsolder joints between electronic components.[citation needed]
Intermetallic particles often form during solidification of metallic alloys, and can be used as adispersion strengthening mechanism.[1]
Examples of intermetallics through history include:
German type metal is described as breaking like glass, without bending, softer than copper, but more fusible than lead.[13]: 454 The chemical formula does not agree with the one above; however, the properties match with an intermetallic compound or an alloy of one.[citation needed]
{{cite book}}: CS1 maint: location missing publisher (link)E02715
{{cite journal}}: CS1 maint: DOI inactive as of July 2025 (link)