Prediction of ω phase formation in Ti–Al–X alloys

The ω phase can form in TiAl based alloys from a precursor high temperature bcc type phase of A2 or B2 structure. The different structures of ω and the stability of the ω phase are discussed with reference to the role of Al and transition metal alloying additions to Ti. Experimental data on ω phase stability for TiAl–X based alloys follows the same trend as for Ti–TM alloys in a general plot of the crystallographic parameter, Δ, versus the free electron per atom per volume of unit cell, φ, of the beta phase of the A2 or B2 structure. It is unlikely that the formation of 3D ω phase could be avoided in TiAl–X alloys when φ<0.135.