Intermetallic

An intermetallic compound (specifically, an intermetallic phase ) is a homogeneous chemical connection of two or more metals. They show, in contrast to alloys lattice structures that differ from those of the constituent metals. In their grids there is a mixing of a metallic bond bond content and lower atomic bonding or ion bonding components, resulting in superlattices.

Structure and properties

There are intermetallic compounds with a stoichiometric composition according to the usual valencies of the metals, and there are intermetallic phases that have more or less extensive areas of homogeneity in the phase diagram. A range of homogeneity, also called phase width, it indicates the limits between which the ratio of the various metals may vary.

Intermetallic compounds are often hard ( high hardness, brittleness, strength) and also chemically highly resistant ( corrosion resistance). They generally have a high melting point and electrical resistance is usually an order of magnitude higher than that of pure transition metals. There are also connections with semiconductor properties and some compounds are distinguished even by special magnetic or superconducting properties.

The specific physical and mechanical properties of such compounds resulting from the particularly strong bond between the dissimilar atoms, which is mainly metallic, with more or less large proportions of other types of bonds ( ionic, covalent bond ).

They thus occupy an intermediate position between metallic alloys and ceramics.

Production

Are produced intermetallic phases both by powder metallurgy as well as by conventional melting method, the preparation and processing can be difficult because of their mechanical properties.

Examples

Examples of intermetallic phases are:

• Laves phase
• Heusler phases
• Zintl phases
• Hume -Rothery phases, which always have fixed valence electron
• NiTi ( shape memory alloy)
• SmCo5 ( magnetic material)
• Nb3Sn ( superconductor )
• Ni3Al in nickel -base superalloys
• NiAl, TiCr2, TaFeAl (experimental high-temperature materials )

• Mg2Si, titanium aluminides Ti3Al and TiAl (experimental high-temperature light-weight materials )
• FeCr, σ - phase high-alloy chromium and chromium -nickel steels can lead to undesirable embrittlement and is therefore avoided by choosing the alloy composition

• So-called MAX - layers, ie materials of stoichiometry Mn 1 AX n, resulting from a transition metal M, a main group element ( engl. A -group, mostly IIIA or IVA ) and a carbon or nitrogen in Part X composed, as tisic

Even higher-alloyed bronze and brass alloys consist of intermetallic phases, which, however, here can arise in various mixing ratios in different forms ( for example, Cu3Sn and Cu3Sn5 ). If the proper mixture ratio is not exactly achieved so classic form alloys, but from the different intermetallic phases, which are the mixing ratio of the next.

Use

Intermetallic compounds have in their use as high melting point, high strength alloys, superconductors, permanent magnetic materials, metallic glasses, etc. great industrial importance. They also play a crucial role in the precipitation of aluminum and nickel alloys and maraging steels.