Intermetallics

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Intermetallics are alloys of two or more metals in a certain proportion, thereby forming a new chemical compound. The resulting compounds are chemically different from either of the two alloying agents, and offer additional benefits or drawbacks, depending on the intended use of the alloy. A commonly used example of an intermetallic is cementite - Fe₃C, present in many steels.

Intermetallics is the short summarizing designation for such intermetallic phases and compounds, i.e. chemical compounds between two or more metals with crystal structures which differ from those of the constituent metals. In a mechanical context, such compounds 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, superconducting 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 superalloys, 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.

Intermetallics of aluminium and gold are a significant cause of wire bond failures in semiconductor devices and other microelectronics devices. There are five of them - the AuAl₂ one is known as purple plague, the others are collectively known as white plague.

[edit] References

Intermetallic Compounds, Vol. 3: Progress, edited by J. H. Westbrook and R. L. Fleischer, John Wiley & Sons, Chichester 2002, 1086 pages.
Intermetallic Compounds - Principles and Practice, edited by J. H. Westbrook and R. L. Fleischer, John Wiley & Sons, Chichester 1995, 2 volumes.
G. Sauthoff: Intermetallics, Wiley-VCH, Weinheim 1995, 165 pages.