Statistical-thermodynamic description of the order–disorder transformation of D019-type phase in Ti–Al alloy

Within the framework of the self-consistent field approximation and the static concentration waves approach, a statistical-thermodynamic description of D019-type superstructure in Ti–Al alloy is developed. A model of order–disorder phase transformation is applied for the non-stoichiometric intermetallic Ti3Al phase. Interatomic-interaction parameters are estimated for both approximations. One model supposes temperature-independent interatomic-interaction parameters, while the other includes the temperature dependence of mixing energies. The partial phase diagrams (equilibrium compositions for the coexistent ordered α2-phase and disordered α-phase) are evaluated for both cases.