TABLE OF CONTENTS An intermetallic is a compound phase of two or more normal metals (ordered or disordered). Interest in intermetallics waned in the 1960s and 1970s. However, the demand for materials that are strong, stiff, and ductile at high temperatures has led to a resurgence of interest in intermetallics, especially silicides and ordered intermetallics such as aluminides. A testimony to this resurgence was the appearance in 1994 on the subject of a two-volume set by J. H. Westbrook and R. L. Fleischer, Intermetallic Compounds: Principles and Practice (New York: John Wiley). Intermetallic aluminides and silicides can be very oxidation and corrosion resistant, because they form strongly adherent surface oxide films. Also, intermetallics span a wide range of unusual properties. An important example outside the field of high-temperature materials involves the exploitation of martensitic transformations, exotic colors, and the phenomenon of shape memory in gold-based intermetallics in jewelry making. In what follows, we first describe the silicides, then the ordered intermetallics, and finally the basic structure and properties of foams.
About 300 intermetallic compounds melt at temperatures above 1,500 C. A survey of some silicide intermetallics for high-temperature applications showed that, based on criteria such as availability, phase changes in the temperature range of interest, and oxidation resistance, Ti 5S 3 and MoSi 2 seem to be the most promising materials: Ti 5Si 3 has the lowest density of all intermetallics, and MoSi 2 has a superior oxidation resistance. For service at...
