intermetallic

In 1967 {{interlanguage link|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.G. E. R. Schulze: Metallphysik, Akademie-Verlag, Berlin 1967 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:{{cn|date=March 2025}}

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

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.{{cn|date=March 2025}}

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.{{cn|date=January 2024}}

The term intermetallic is used{{Cotton&Wilkinson6th}} 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.{{cite news|title=Wings of steel: An alloy of iron and aluminium is as good as titanium, at a tenth of the cost|url=https://www.economist.com/news/science-and-technology/21642107-alloy-iron-and-aluminium-good-titanium-tenth|access-date=February 5, 2015|newspaper=The Economist|date=February 7, 2015|quote=E02715}}

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.{{Cite book|last=Soboyejo|first= W. O.|url=http://worldcat.org/oclc/300921090|title=Mechanical properties of engineered materials|date=2003|publisher=Marcel Dekker|isbn=0-8247-8900-8|chapter=12.5 Fracture of Intermetallics|oclc=300921090}} 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.{{cn|date=March 2025}}

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.{{Cite journal |date=June 1993 |title=Metallization: theory and practice for VLSI and ULSI |journal=Choice Reviews Online |volume=30 |issue=10 |pages=30–5612-30-5612 |doi=10.5860/choice.30-5612 |issn=0009-4978|first=S.P. |last=Murarka |doi-broken-date=1 February 2025 }} 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{{cite book

| last = Ohring | first = Milton | title = Materials Science of Thin Films | publisher = Academic Press | year = 2002 | isbn = 9780125249751 | url = {{google books|plainurl=y|id=50jZ8a3_hZgC}} }}{{rp| 692}}

• 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 devices and other microelectronics devices. The management of intermetallics is a major issue in the reliability of solder joints between electronic components.{{cn|date=January 2024}}

{{Main|Intermetallic particle}}

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

Examples of intermetallics through history include:

• Roman yellow brass, CuZn
• Chinese high tin bronze, Cu₃₁Sn₈
• Type metal, SbSn
• Chinese white copper, CuNi {{cite web|url=http://www.chinatoday.com.cn/English/e20026/sunzi1.htm|title=The Art of War by Sun Zi: A Book for All Times|publisher=China Today|access-date=2022-11-25|archive-date=2005-03-07|archive-url=https://web.archive.org/web/20050307083704/http://www.chinatoday.com.cn/English/e20026/sunzi1.htm|url-status=dead}}

German type metal is described as breaking like glass, without bending, softer than copper, but more fusible than lead.{{Cite book |first=George |last=Long |url={{google books|plainurl=y|id=joN6G1T6ZHIC}}|title=The Penny Cyclopædia of the Society for the Diffusion of Useful Knowledge |chapter=Type-pounding|date=1843 |publisher=C. Knight |language=en}}{{rp|454}} The chemical formula does not agree with the one above; however, the properties match with an intermetallic compound or an alloy of one.{{cn|date=January 2024}}

• Complex metallic alloys
• Kirkendall effect
• Maraging steel
• Metallurgy
• Solid solution

• {{cite book |last=Sauthoff |first=Gerhard |author-link=:de:Gerhard Sauthoff |url={{google books|plainurl=y|id=p75RAAAAMAAJ}} |title=Intermetallics |publisher=Wiley-VCH |year=1995 |isbn=978-3527293209 |pages=1–165}}
• {{cite book |last=Sauthoff |first=Gerhard |author-link=:de:Gerhard Sauthoff |chapter=Intermetallics |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2006 |publisher=Wiley Interscience |doi=10.1002/14356007.e14_e01.pub2 |pages=393–423|isbn=978-3-527-30385-4 }}

• [http://www.elsevier.com/wps/find/journaldescription.cws_home/423924/description#description Intermetallics], scientific journal
• {{cite web|url=http://nepp.nasa.gov/wirebond/intermetallic_creation_and_growt.htm|archive-url=https://web.archive.org/web/20051218202657/http://nepp.nasa.gov/wirebond/intermetallic_creation_and_growt.htm |archive-date=December 18, 2005 |title=Intermetallic Creation and Growth}}
• {{Cite web |title=IMPRESS Intermetallics project |url=http://www.spaceflight.esa.int/impress#IMPRESS |access-date=2024-12-22 |website=www.spaceflight.esa.int

|archive-url=https://web.archive.org/web/20070329034903/http://www.spaceflight.esa.int/impress/#IMPRESS |archive-date=2007-03-29 }}

• {{cite AV media|url=https://www.ameslab.gov/mpc/video |archive-url=https://web.archive.org/web/20151210223620/https://www.ameslab.gov/mpc/video |archive-date=December 10, 2015|title=Video of an AB₅ intermetallic compound solidifying/freezing}}

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