Phase selection in non-equilibrium processed TM–Al intermetallic alloys

Phase transformations, including the A2→B2 transformation and ω phase formation, in TM–Al and TM–Al–X alloys (TM=Ti, Nb, Fe and X=Cr, V, Mo) are discussed using microstructural data and nucleation theory coupled with phase equilibria calculations. The ω phase can form from a precursor bcc type phase of A2 or B2 structure. The stability of the ω phase is discussed. Experimental data on ω phase stability is shown in a general plot of the crystallographic parameter |Δ| versus the free electron per atom per volume of unit cell of the beta phase of the A2 or B2 structure.