Chapter 24 - Mechanical Properties of Intermetallic Compounds

Abstract

Intermetallic compounds have a number of properties in addition to strength that make them intrinsically more appealing than disordered alloys for high-temperature use. First, intermetallic compounds tend to be intrinsically very strong (high yield or fracture stress) and the strength tends to be maintained up to high temperatures. Not only is the strength of intermetallic compounds maintained to high temperatures, the modulus also tends to be high and tends to decrease more slowly with increasing temperature than does that of disordered alloys. This chapter focuses on three compounds: a material with the fcc-derivative Ll2 structure—Ni3Al; the bcc-derivative B2 structure—NiAl; and the tetragonal Ll0 structure—TiAl. It provides a review of the mechanical properties of intermetallic compounds. Because plasticity is the basic property that links all these properties together, it focuses on dislocation plasticity with emphasis on the relationship between dislocation core structures and plastic properties. It discusses the plastic behavior of Ni3A1, NiAl, and TiAl; the macroscopic flow behavior is related to the nature of the dislocation dissociation observed in these materials, on both the macroscopic and the atomistic level.