Intermetallic alloys represent a unique class of materials with atomic arrangements that are different from those of conventional disordered alloys. Among them are alloys based on Ni ₃ Al, Fe ₃ Al, and TiAl. Intermetallic alloys have unique properties, such as high melting point, low density, high-temperature strength, and high-temperature corrosion and oxidation resistance. Their only disadvantage is the lack of ductility at room temperature and at elevated temperatures. However, they can be ductilised by micro- and macroalloying. Application of intermetallic alloys for structural use at elevated temperature depends on their ability to be welded using conventional welding procedures. This paper focuses on the development of these alloys, their behaviour when subjected to weld thermal cycles, and their weldability. Most intermetallic alloys are susceptible to cracking during or after welding, but some can be modified to have good weldability. The paper discusses welding and weldability of Ni ₃ Al-, Fe ₃ Al-, and TiAl-based intermetallic alloys. In addition, the weldability of other long-range ordered alloys, of the type (Fe, Ni) ₃ V and (Fe, Co) ₃ V, are briefly discussed.

Theoretical electronic-structure calculations have been carried out to examine the site occupancy of $3d$ transition-metal impurities in ${\mathrm{Fe}}_3\mathrm{Al}.$ Our studies based on the first-principles gradient-corrected density-functional formalism and carried over representative clusters show that the site occupancy is related to the strength and the nature of magnetic interactions. Impurities to the left of Fe couple antiferromagnetically to Fe and prefer ${\mathrm{Fe}}_{\mathrm{I}}$ sites while the impurities to the right (Co and Ni) couple ferromagnetically and prefer ${\mathrm{Fe}}_{\mathrm{II}}$ sites. The nature of coupling between impurities, Fe and Al sites is examined and its implications on controlling the magnetic behavior is highlighted.