Intermetallic

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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 intermetallic compounds. [1]

Contents

Although the term "intermetallic compounds", as it applies to solid phases, has been in use for many years, Hume-Rothery has argued that it gives misleading intuition, suggesting a fixed stoichiometry and even a clear decomposition into species. [4]

Definitions

Research definition

Schulze in 1967 [5] 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. Under this definition, the following are included:

  1. Electron (or Hume-Rothery) compounds
  2. Size packing phases. e.g. Laves phases, Frank–Kasper phases and Nowotny phases
  3. Zintl phases

The definition of a metal is taken to include:

  1. post-transition metals, i.e. aluminium, gallium, indium, thallium, tin, lead, and bismuth.
  2. metalloids, e.g. silicon, germanium, arsenic, antimony and tellurium.

Homogeneous and heterogeneous solid solutions of metals, and interstitial compounds such as the carbides and nitrides are excluded under this definition. However, interstitial intermetallic compounds are included, as are alloys of intermetallic compounds with a metal.

Common use

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 similar properties to the intermetallic compounds defined above.[ citation needed ]

Complexes

The term intermetallic is used [6] to describe compounds involving two or more metals such as the cyclopentadienyl complex Cp6Ni2Zn4.

B2

A B2 intermetallic compound has equal numbers of atoms of two metals such as aluminium and iron, arranged as two interpenetrating simple cubic lattices of the component metals. [7]

Properties and applications

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, there are some examples of intermetallics with ductile fracture modes such as Nb–15Al–40Ti. Other intermetallics 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 in many intermetallics. [8] They often 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 also 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. Some 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 also attracted interest for turbine blade applications, while the latter is also used in very small quantities for grain refinement of titanium alloys. Silicides, inter-metallic involving silicon, are utilized as barrier and contact layers in microelectronics. [9]

Physical properties of intermetallics [1]
Intermetallic CompoundMelting Temperature

(°C)

Density

(kg/m3)

Young's Modulus (GPa)
FeAl1250–14005600263
Ti3Al16004200210
MoSi220206310430

Examples

  1. Magnetic materials e.g. alnico, sendust, Permendur, FeCo, Terfenol-D
  2. Superconductors e.g. A15 phases, niobium-tin
  3. Hydrogen storage e.g. AB5 compounds (nickel metal hydride batteries)
  4. Shape memory alloys e.g. Cu-Al-Ni (alloys of Cu3Al and nickel), Nitinol (NiTi)
  5. Coating materials e.g. NiAl
  6. High-temperature structural materials e.g. nickel aluminide, Ni3Al
  7. Dental amalgams, which are alloys of intermetallics Ag3Sn and Cu3Sn
  8. Gate contact/ barrier layer for microelectronics e.g. TiSi2 [10]
  9. Laves phases (AB2), e.g., MgCu2, MgZn2 and MgNi2.

The 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

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

History

Examples of intermetallics through history include:

  1. Roman yellow brass, CuZn
  2. Chinese high tin bronze, Cu31Sn8
  3. Type metal, SbSn
  4. Chinese white copper, CuNi [11]

German type metal is described as breaking like glass, not bending, softer than copper but more fusible than lead. [12] 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 ]

See also

Related Research Articles

<span class="mw-page-title-main">Alloy</span> Mixture or metallic solid solution composed of two or more elements

An alloy is a mixture of chemical elements of which in most cases at least one is a metallic element, although it is also sometimes used for mixtures of elements; herein only metallic alloys are described. Most alloys are metallic and show good electrical conductivity, ductility, opacity, and luster, and may have properties that differ from those of the pure elements such as increased strength or hardness. In some cases, an alloy may reduce the overall cost of the material while preserving important properties. In other cases, the mixture imparts synergistic properties such as corrosion resistance or mechanical strength.

<span class="mw-page-title-main">Metal</span> Type of material

A metal is a material that, when polished or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. These properties are all associated with having electrons available at the Fermi level, as against nonmetallic materials which do not. Metals are typically ductile and malleable.

<span class="mw-page-title-main">Metallic bonding</span> Type of chemical bond in metals

Metallic bonding is a type of chemical bonding that arises from the electrostatic attractive force between conduction electrons and positively charged metal ions. It may be described as the sharing of free electrons among a structure of positively charged ions (cations). Metallic bonding accounts for many physical properties of metals, such as strength, ductility, thermal and electrical resistivity and conductivity, opacity, and lustre.

<span class="mw-page-title-main">Solder</span> Alloy used to join metal pieces

Solder is a fusible metal alloy used to create a permanent bond between metal workpieces. Solder is melted in order to wet the parts of the joint, where it adheres to and connects the pieces after cooling. Metals or alloys suitable for use as solder should have a lower melting point than the pieces to be joined. The solder should also be resistant to oxidative and corrosive effects that would degrade the joint over time. Solder used in making electrical connections also needs to have favorable electrical characteristics.

<span class="mw-page-title-main">Brazing</span> Metal-joining technique

Brazing is a metal-joining process in which two or more metal items are joined by melting and flowing a filler metal into the joint, with the filler metal having a lower melting point than the adjoining metal.

<span class="mw-page-title-main">Maraging steel</span> Steel known for strength and toughness

Maraging steels are steels that are known for possessing superior strength and toughness without losing ductility. Aging refers to the extended heat-treatment process. These steels are a special class of very-low-carbon ultra-high-strength steels that derive their strength not from carbon, but from precipitation of intermetallic compounds. The principal alloying element is 15 to 25 wt% nickel. Secondary alloying elements, which include cobalt, molybdenum and titanium, are added to produce intermetallic precipitates.

<span class="mw-page-title-main">Raney nickel</span> Chemical compound

Raney nickel, also known as the primary catalyst for the Cormas-Grisius Electrophilic Benzene Addition, is a fine-grained solid composed mostly of nickel derived from a nickel–aluminium alloy. Several grades are known, of which most are gray solids. Some are pyrophoric, but most are used as air-stable slurries. Raney nickel is used as a reagent and as a catalyst in organic chemistry. It was developed in 1926 by American engineer Murray Raney for the hydrogenation of vegetable oils. Raney Nickel is a registered trademark of W. R. Grace and Company. Other major producers are Evonik and Johnson Matthey.

<span class="mw-page-title-main">Titanium alloys</span> Metal alloys made by combining titanium with other elements

Titanium alloys are alloys that contain a mixture of titanium and other chemical elements. Such alloys have very high tensile strength and toughness. They are light in weight, have extraordinary corrosion resistance and the ability to withstand extreme temperatures. However, the high cost of processing limits their use to military applications, aircraft, spacecraft, bicycles, medical devices, jewelry, highly stressed components such as connecting rods on expensive sports cars and some premium sports equipment and consumer electronics.

<span class="mw-page-title-main">Superalloy</span> Alloy with higher durability than normal metals

A superalloy, or high-performance alloy, is an alloy with the ability to operate at a high fraction of its melting point. Key characteristics of a superalloy include mechanical strength, thermal creep deformation resistance, surface stability, and corrosion and oxidation resistance.

An aluminide is a compound that has aluminium with other elements. Since aluminium is near the nonmetals on the periodic table, it can bond with metals differently than other metals. The properties of an aluminide are between those of a metal alloy and those of an ionic compound. Aluminides are used as bond coats in thermal barrier coating systems.

Magnesium aluminide is an intermetallic compound of magnesium and aluminium. Common phases (molecular structures) include the beta phase (Mg2Al3) and the gamma phase (Mg17Al12), which both have cubic crystal structures. Magnesium aluminides are important constituents of 5XXX aluminium alloys (aluminium-magnesium) and magnesium-aluminium alloys, determining many of their engineering properties. Due to the advantage of low density and being strong, magnesium aluminide is important for aircraft engines. MgAl has also been investigated for use as a reactant to produce metal hydrides in hydrogen storage technology. Like many intermetallics, MgAl compounds often have unusual stoichiometries with large and complex unit cells.

Titanium aluminide, commonly gamma titanium, is an intermetallic chemical compound. It is lightweight and resistant to oxidation and heat, but has low ductility. The density of γ-TiAl is about 4.0 g/cm3. It finds use in several applications including aircraft, jet engines, sporting equipment and automobiles. The development of TiAl based alloys began circa 1970. The alloys have been used in these applications only since about 2000.

<span class="mw-page-title-main">Alloy steel</span> Steel alloyed with a variety of elements

Alloy steel is steel that is alloyed with a variety of elements in amounts between 1.0% and 50% by weight, typically to improve its mechanical properties.

In metallurgy, solid solution strengthening is a type of alloying that can be used to improve the strength of a pure metal. The technique works by adding atoms of one element to the crystalline lattice of another element, forming a solid solution. The local nonuniformity in the lattice due to the alloying element makes plastic deformation more difficult by impeding dislocation motion through stress fields. In contrast, alloying beyond the solubility limit can form a second phase, leading to strengthening via other mechanisms.

Nickel aluminide refers to either of two widely used intermetallic compounds, Ni3Al or NiAl, but the term is sometimes used to refer to any nickel–aluminium alloy. These alloys are widely used because of their high strength even at high temperature, low density, corrosion resistance, and ease of production. Ni3Al is of specific interest as a precipitate in nickel-based superalloys, where it is called the γ' (gamma prime) phase. It gives these alloys high strength and creep resistance up to 0.7–0.8 of its melting temperature. Meanwhile, NiAl displays excellent properties such as lower density and higher melting temperature than those of Ni3Al, and good thermal conductivity and oxidation resistance. These properties make it attractive for special high-temperature applications like coatings on blades in gas turbines and jet engines. However, both these alloys have the disadvantage of being quite brittle at room temperature, with Ni3Al remaining brittle at high temperatures as well. To address this problem, has been shown that Ni3Al can be made ductile when manufactured in single-crystal form rather than in polycrystalline form.

<span class="mw-page-title-main">Colored gold</span> Various colors of gold obtained by alloying gold with other elements

Colored gold is the name given to any gold that has been treated using techniques to change its natural color. Pure gold is slightly reddish yellow in color, but colored gold can come in a variety of different colors by alloying it with different elements.

Reactive multi-layer foils are a class of reactive materials, sometimes referred to as a pyrotechnic initiator of two mutually reactive metals, sputtered to form thin layers that create a laminated foil. On initiation by a heat pulse, delivered by a bridge wire, a laser pulse, an electric spark, a flame, or by other means, the metals undergo self-sustaining exothermic reaction, producing an intermetallic compound. The reaction occurs in solid and liquid phase only, without releasing any gas.

<span class="mw-page-title-main">Post-transition metal</span> Category of metallic elements

The metallic elements in the periodic table located between the transition metals to their left and the chemically weak nonmetallic metalloids to their right have received many names in the literature, such as post-transition metals, poor metals, other metals, p-block metals and chemically weak metals. The most common name, post-transition metals, is generally used in this article.

Iron aluminides are intermetallic compounds of iron and aluminium - they typically contain ~18% Al or more.

References

  1. 1 2 3 4 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.{{cite book}}: CS1 maint: location missing publisher (link)
  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) [1948]. Electrons, atoms, metals and alloys (revised ed.). London: Louis Cassier Co., Ltd. pp. 316–317 – via the Internet Archive.
  5. ↑ G. E. R. Schulze: Metallphysik, Akademie-Verlag, Berlin 1967
  6. ↑ 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
  7. ↑ "Wings of steel: An alloy of iron and aluminium is as good as titanium, at a tenth of the cost". The Economist. February 7, 2015. Retrieved February 5, 2015. E02715
  8. ↑ Soboyejo, W. O. (2003). "12.5 Fracture of Intermetallics". Mechanical properties of engineered materials. Marcel Dekker. ISBN   0-8247-8900-8. OCLC   300921090.
  9. ↑ S.P. Murarka, Metallization Theory and Practice for VLSI and ULSI. Butterworth-Heinemann, Boston, 1993.
  10. ↑ Milton Ohring, Materials Science of Thin Films, 2nd Edition, Academic Press, San Diego, CA, 2002, p. 692.
  11. ↑ "The Art of War by Sun Zi: A Book for All Times". China Today. Archived from the original on 2005-03-07. Retrieved 2022-11-25.
  12. ↑ Type-pounding The Penny Cyclopædia of the Society for the Diffusion of Useful Knowledge By Society for the Diffusion of Useful Knowledge (Great Britain), George Long Published 1843
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