Novel ordering transitions in off- stoichiometric γ-TiAl intermetallics and the similarities between these and the special point ordering processes in Ni-Mo alloys

摘要

Ordering on Ti-rich(002)planes of Al-rich γ-TiAl (Li_0) phase can be described in terms of evol- ution of superlattice structures consisting of space filling arrangements of two-dimensional(2D) motifs of different shapes. These 2d structural units (tiles) comprising unimolecular clusters of Ti_2Al, Ti_3Al and Ti_4Al stoichiometries and having the shapes of lean and fat rhombi and squares respectively, either singly Or in combinations, constitute the building blocks of this variety of superlattice structures.