Intermetallic
Type of metallic alloy From Wikipedia, the free encyclopedia
Type of metallic alloy From Wikipedia, the free encyclopedia
An intermetallic (also called intermetallic compound, intermetallic alloy, ordered intermetallic alloy, long-range-ordered alloy) is a type of metallic alloy 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.[1][2][3] They can be classified as stoichiometric or nonstoichiometic.[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 into species.[4]
In 1967 Schulze 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.[5] This definition includes:
The definition of metal includes:
Homogeneous and heterogeneous solid solutions of metals, and interstitial compounds such as carbides and nitrides are excluded under this definition. However, interstitial intermetallic compounds are included, as are alloys of intermetallic compounds with a metal.
In common use, the research definition, including post-transition metals and metalloids, is extended to include compounds such as cementite, Fe3C. These compounds, sometimes termed interstitial compounds, can be stoichiometric, and share properties with the above intermetallic compounds.[citation needed]
The term intermetallic is used[6] to describe compounds involving two or more metals such as the cyclopentadienyl complex Cp6Ni2Zn4.
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.[7]
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 by alloying with other elements to increase grain boundary cohesion. Alloying of other materials such as boron to improve grain boundary cohesion can improve ductility.[8] They may offer a compromise between ceramic and metallic properties when hardness and/or resistance to high temperatures is important enough to sacrifice some toughness and ease of processing. They can display desirable magnetic and chemical properties, due to their strong internal order and mixed (metallic and covalent/ionic) bonding, respectively. Intermetallics have given rise to various novel materials developments.
| 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 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 aluminides have attracted interest for turbine blade applications, while the latter is also used in small quantities for grain refinement of titanium alloys. Silicides, intermetallics involving silicon, serve as barrier and contact layers in microelectronics.[9] Others include:
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 devices and other microelectronics devices. The management of intermetallics is a major issue in the reliability of solder joints between electronic components.[citation needed]
Intermetallic particles often form during solidification of metallic alloys, and can be used as a dispersion 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.[12]: 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]
Seamless Wikipedia browsing. On steroids.
Every time you click a link to Wikipedia, Wiktionary or Wikiquote in your browser's search results, it will show the modern Wikiwand interface.
Wikiwand extension is a five stars, simple, with minimum permission required to keep your browsing private, safe and transparent.
