Intermetallic

An intermetallic is a type of metallic alloy that forms an ordered solid-state compound between two or more metallic elements. Alternatively, it can be called intermetallic compound, intermetallic alloy, ordered intermetallic alloy, or long-range-ordered alloy. 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]

Recent advances in intermetallic crystal chemistry have led to the discovery of a new family of ternary intermetallic compounds known as ZIP phases. These materials exhibit so-called dualistic atomic ordering, in which different atomic sublattices demonstrate distinct ordering mechanisms within a single crystalline framework. ZIP phases can crystallize in both face-centered cubic and hexagonal structural variants, thereby expanding the known structural diversity of complex intermetallic systems.[5]

## Contents

* 1 Definitions
* 1.1 Research definition
* 1.2 Common use
* 1.3 Complexes
* 1.4 B2
* 2 Properties
* 3 Applications
* 4 Intermetallic particles
* 5 Undesired examples
* 6 History
* 7 See also
* 8 References
* 9 Sources
* 10 External links

## Definitions

### Research definition

In 1967 Gustav Ernst Robert Schulze [de; de] 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.[6] This definition includes:

* Electron (or Hume-Rothery) compounds
* Size packing phases. e.g., Laves phases, Frank–Kasper phases[7] and Nowotny phases
* Zintl phases

* Post-transition metals, i.e. aluminium, gallium, indium, thallium, tin, lead, and bismuth.
* Metalloids, e.g., silicon, germanium, arsenic, antimony and tellurium.

### Common use

### Complexes

The term intermetallic is used[8] to describe compounds involving two or more metals such as the cyclopentadienyl complex Cp6Ni2Zn4.

### B2

Al-Ni B2 structure (lattice parameter: 2.86 A) viewed from [100], [110], [111], and [112] directions.

A B2 (also known as cesium chloride structure type) intermetallic compound has equal numbers of atoms of two metals, such as aluminium-iron, and aluminium-nickel, arranged as two interpenetrating simple cubic lattices of the component metals.[9]

## Properties

Intermetallic compounds are generally brittle at room temperature and have high melting 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 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.[10] 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. {| class="wikitable" |+Physical properties of intermetallics[1] !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 |}

## 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 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.[11] Others include:

* Magnetic materials e.g., alnico, sendust, Permendur, FeCo, Terfenol-D
* Superconductors 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 (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 microelectronics e.g., TiSi2[12]: 692
* Laves phases (AB2), e.g., MgCu2, MgZn2 and MgNi2.

## Intermetallic particles

Main article: Chemistry:Intermetallic particle

Intermetallic particles often form during solidification of metallic alloys, and can be used as a dispersion strengthening mechanism.[1]

## Undesired examples

The intermetallic compounds formed by tin are hard and brittle. Some compounds of importance in electronics are Ag
3Sn, Cu
3Sn, and Cu
6Sn
5. As these particles grow they tend to compromise the integrity of a solder joint made by lead-free solder.[13] Some additives can reduce the grain size of IMC and disperse them, turning them into strengthing elements.[14]

## History

Examples of intermetallics through history include:

* Roman yellow brass, CuZn
* Chinese high tin bronze, Cu31Sn8
* Type metal, SbSn
* Chinese white copper, CuNi [15]

German type metal is described as breaking like glass, without bending, softer than copper, but more fusible than lead.[16]: 454 The chemical formula does not agree with the one above; however, the properties match with an intermetallic compound or an alloy of one.

## See also

* Complex metallic alloys
* Kirkendall effect
* Maraging steel
* Metallurgy
* Solid solution
* Strukturbericht designation
* Order and disorder

## References

1. ↑ 1.0 1.1 1.2 1.3 Askeland, Donald R.; Wright, Wendelin J. (January 2015). "11-2 Intermetallic Compounds". The science and engineering of materials (Seventh ed.). Boston, MA. pp. 387–389. ISBN 978-1-305-07676-1. OCLC 903959750.
2. ↑ Panel On Intermetallic Alloy Development, Commission On Engineering And Technical Systems (1997). Intermetallic alloy development: a program evaluation. National Academies Press. p. 10. ISBN 0-309-52438-5. OCLC 906692179.
3. ↑ Soboyejo, W. O. (2003). "1.4.3 Intermetallics". Mechanical properties of engineered materials. Marcel Dekker. ISBN 0-8247-8900-8. OCLC 300921090.
4. ↑ Hume-Rothery, W. (1955). Electrons, atoms, metals and alloys (revised ed.). London: Louis Cassier Co., Ltd. pp. 316–317. https://archive.org/details/in.ernet.dli.2015.18295.
5. ↑ Tunes, M. A.; Drewry, S. M.; Schmidt, F. (2026). "A New Family of Ternary Intermetallic Compounds with Dualistic Atomic Ordering – The ZIP Phases". Advanced Materials 38 (8). doi:10.1002/adma.202308168.
6. ↑ G. E. R. Schulze: Metallphysik, Akademie-Verlag, Berlin 1967
7. ↑ Frank, F. C.; Kasper, J. S. (10 March 1958). "Complex alloy structures regarded as sphere packings. I. Definitions and basic principles". Acta Crystallographica 11 (3): 184–190. doi:10.1107/S0365110X58000487. Bibcode: 1958AcCry..11..184F.
8. ↑ Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A.; Bochmann, Manfred (1999), Advanced Inorganic Chemistry (6th ed.), New York: Wiley-Interscience, ISBN 0-471-19957-5
9. ↑ "Wings of steel: An alloy of iron and aluminium is as good as titanium, at a tenth of the cost". The Economist. 7 February 2015. https://www.economist.com/news/science-and-technology/21642107-alloy-iron-and-aluminium-good-titanium-tenth. "E02715"
10. ↑ Soboyejo, W. O. (2003). "12.5 Fracture of Intermetallics". Mechanical properties of engineered materials. Marcel Dekker. ISBN 0-8247-8900-8. OCLC 300921090.
11. ↑ Murarka, S.P. (June 1993). "Metallization: theory and practice for VLSI and ULSI". Choice Reviews Online 30 (10): 30–5612–30-5612. doi:10.5860/choice.30-5612. ISSN 0009-4978.
12. ↑ Ohring, Milton (2002). Materials Science of Thin Films. Academic Press. ISBN 978-0-12-524975-1. https://books.google.com/books?id=50jZ8a3_hZgC.
13. ↑ Nan Jiang (2019). "Reliability issues of lead-free solder joints in electronic devices". Science and Technology of Advanced Materials 20 (1): 876–901. doi:10.1080/14686996.2019.1640072. PMID 31528239. Bibcode: 2019STAdM..20..876J.
14. ↑ Meng Zhao, Liang Zhang, Zhi-Quan Liu, Ming-Yue Xiong, and Lei Sun (2019). "Structure and properties of Sn-Cu lead-free solders in electronics packaging". Science and Technology of Advanced Materials 20 (1): 421–444. doi:10.1080/14686996.2019.1591168. PMID 31489052. Bibcode: 2019STAdM..20..421Z.
15. ↑ "The Art of War by Sun Zi: A Book for All Times". China Today. http://www.chinatoday.com.cn/English/e20026/sunzi1.htm.
16. ↑ Long, George (1843). "Type-pounding" (in en). The Penny Cyclopædia of the Society for the Diffusion of Useful Knowledge. C. Knight. https://books.google.com/books?id=joN6G1T6ZHIC.

## Sources

* Sauthoff, Gerhard (1995). Intermetallics. Wiley-VCH. pp. 1–165. ISBN 978-3-527-29320-9. https://books.google.com/books?id=p75RAAAAMAAJ.
* Sauthoff, Gerhard (2006). "Intermetallics". Ullmann's Encyclopedia of Industrial Chemistry. Wiley Interscience. pp. 393–423. doi:10.1002/14356007.e14_e01.pub2. ISBN 978-3-527-30385-4.

## External links

* Intermetallics, scientific journal
* "Intermetallic Creation and Growth". http://nepp.nasa.gov/wirebond/intermetallic_creation_and_growt.htm.
* "IMPRESS Intermetallics project". http://www.spaceflight.esa.int/impress#IMPRESS.
* Video of an AB5 intermetallic compound solidifying/freezing. Archived from the original on 10 December 2015.

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