Joining

In recent years, ordered intermetallic alloys have attracted considerable interest because of the unique properties that make them attractive candidates for high-temperature structural applications (Stoloff and Davies 1966; Kear et al. 1970; Westbrook 1959, 1967; Lipsitt 1985; Liu 1984; Stoloff 1989). Some of the alloy systems that are currently under development or in use include those based on the following compounds: Ni₃Al, Fe₃Al, Ti₃Al, Co₃V, Ni₃V, TiAl, NiAl, and FeAl. Many of these compounds have low density and high modulus coupled with excellent high-temperature strength, which derives from the unique dislocation dynamics in ordered lattices and slow atomic mobility. Often they have unique oxidation and corrosion properties (Liu and Stiegler 1984). Intermetallic compounds, however, tend to have limited ductility, and this characteristic has deterred their widespread use for structural applications. Recent work has shown that the ductility and fabricability of several ordered intermetallic compounds can be substantially improved using physical metallurgy principles (Liu 1984; Stoloff 1989; Rhodes, Hamilton, and Paton 1987; Liu, White, and Horton 1985). Because of the unique properties of these intermetallic alloys, a wide range of applications is anticipated, ranging from aerospace to land-based transportation systems, energy systems, chemical systems, heating elements, and so on.