An intermetallic is a type of metallicalloy 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]
Definitions
Research definition
In 1967 Gustav Ernst Robert Schulze[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:
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.[citation needed]
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.[citation needed]
The intermetallic compounds formed by tin are hard and brittle. Some compounds of importance in electronics are Ag3Sn, Cu3Sn, and Cu6Sn5. 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:
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.[citation needed]
↑Panel On Intermetallic Alloy Development, Commission On Engineering And Technical Systems (1997). Intermetallic alloy development: a program evaluation. National Academies Press. p.10. ISBN0-309-52438-5. OCLC906692179.
↑Soboyejo, W. O. (2003). "1.4.3 Intermetallics". Mechanical properties of engineered materials. Marcel Dekker. ISBN0-8247-8900-8. OCLC300921090.
↑G. E. R. Schulze: Metallphysik, Akademie-Verlag, Berlin 1967
↑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. Bibcode:1958AcCry..11..184F. doi:10.1107/S0365110X58000487.
↑Soboyejo, W. O. (2003). "12.5 Fracture of Intermetallics". Mechanical properties of engineered materials. Marcel Dekker. ISBN0-8247-8900-8. OCLC300921090.
↑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 (inactive 1 July 2025). ISSN0009-4978.{{cite journal}}: CS1 maint: DOI inactive as of July 2025 (link)
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