A new intermetallic compound in TiAl+Nb composition area of the Ti-Al-Nb ternary system

Nb atom in TiAl was proved to substitute for Ti atom and preferentially occupies the Ti sublattice using ALCHEMI technique. For the case of low Nb content the site occupation of Nb atoms is random on the Ti sublattice. The electron diffraction investigation indicated that when the Nb content is increased to ∼12 at.% the ordered distribution of Nb atoms on the sublattice appears. This is a phenomenon of continuous ordering occurring in the TiAl+Nb system with increasing Nb and Al contents. The development of the continuous ordering finally leads to the formation of a new ternary compound γ1. The structure transition from binary γ-TiAl to γ1-Ti4Nb3Al9 is schematically shown in the paper. High Nb content is favorable for the formation of γ1 phase. Increasing Al content from 50 to 60 at.% is also favorable for the formation of γ1 phase. The phase relationship in the TiAl+Nb area is determined. Various γ1 base alloys with different microstructures can be designed.