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[交流] ［学术交流］橡树岭国家实验室关于intermetallic的描述

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Intermetallic compounds are a unique class of materials, consisting of ordered alloy phases formed between two or more metallic elements where the different atomic species occupy specific sites in the crystal lattice (NRC, 1984; Anton et al., 1989). Intermetallics differ from conventional alloys in that they generally possess long-range-ordered crystal structures at ambient and intermediate temperatures. Intermetallic compounds form in composition ranges close to stoichiometric ratios. Thus, although the laws of chemical valency are usually not followed, the compounds often have relatively simple chemical names like TiAl, Ti3Al, NiAl, Ni3Al, CuZn, Cu3Au, and Nb5Si3.

Intermetallics have characteristics of both metals and ceramics, and their mechanical properties are intermediate between metals (which are generally softer and more ductile) and ceramics (which are generally harder and more brittle). The predominant bonding in ceramics is covalent and ionic, as opposed to metallic bonding. Intermetallics contain both metallic and covalent bonds, depending on the constituent metals. Because of their intermediate position, the properties of intermetallics can be strongly influenced by small changes in the system (i.e., variations in the microstructure can result in changes in strength and ductility over a considerable range).

A great deal of work has been done in the last 10 to 15 years to develop and characterize intermetallics and to develop processing technologies. In response to the need for low density, high performance alloys for use in the components of airframes and turbine engines (NRC, 1993, 1996), for example, concerted efforts have been made in recent years to improve the properties of intermetallic alloys, especially alloys based on aluminides (e.g., TiAl, Ti3Al, NiAl, Ni3Al, FeAl,Fe3Al). Their inherent oxidation resistance and retention of strength at high, homologous temperatures make them prime candidates for use at intermediate temperature ranges, where creep resistant alloys are required. The major problem with many intermetallics is that they can have extremely low ductility at ambient temperatures. Therefor, before they can be used as structural materials, intermetallics must be modified to improve their ductility and strength and to make them more resistant to oxidation and corrosion. In addition, processes must be developed for preparing and processing these materials into usable shapes.

[ Last edited by mainpro on 2006-10-17 at 23:10 ]

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