Applications of Intermetallic Compounds

Abstract

Just what is an intermetallic compound? An intermetallic compound is a true compound of two or more metals that has a distinctive structure in which the metallic constituents are in relatively fixed abundance ratios and are usually ordered on two or more sublattices, each with its own distinct population of atoms. Often substantial or complete disorder may be obtained as a result of a low ordering energy or the intervention of some external agency—for example, extreme cooling rates or radiation. Deviations from precise stoichiometry are common on one or both sides of the nominal atomic ratio, necessitating some misordering and/or the introduction of vacancies. Usually metal-metalloid compounds such as silicides, arsenides, or tellurides are also included in the category since the phenomenology of most such compounds is similar to that of metal-metal compounds. More than 25,000 distinct intermetallics are now known.To many, intermetallic compounds (IMCs) are classed as “exotics” or “advanced materials.” Such categorization should apply only to the recent interest in their potential use as monolithic high-temperature structural materials. Actually IMCs have been used for thousands of years in an astonishing range of applications exploiting not only their mechanical properties but their chemical, electrical, magnetic, optical, and semiconducting properties as well. Most readers will be surprised to learn that they carry within their own bodies (dental fillings) or on their persons (jewelry or pocket lighters) IMCs for which selection and processing are uniquely appropriate to those applications. The economic impact of IMCs is as unappreciated as the diversity of their applications. Some are regularly produced in quantities of 1,000s of tons per year while others, although not in tonnage production, are key factors in devices with billion-dollar markets.