Structure Maps for Ordered Intermetallics

The search for new pseudobinary intermetallics with a required structure type and mechanical properties can be guided at the outset by the use of phenomenological two-dimensional structure maps which order the known structural data base on binary compounds. This paper reviews the progress made and problems encountered in using the maps in developing new cubic transition metal aluminides. In particular, it emphasizes the need for a microscopic quantum mechanical understanding of why, for example, Al₃Nb cannot be stabilized in the cubic form whereas Al₃Ti can, and why the latter remains brittle even though single crystals of Ni₃Al with the same cubic L1₂ crystal structure are ductile.