Thermodynamic modelling of the order-disorder transformation of the orthorhombic phase of the Al-Nb-Ti system

The order/disorder transformation of the orthorhombic phase of the Al-Nb-Ti system has been modelled using the sublattice formalism with the aim of representing the thermodynamic properties of the two states, ordered and disordered, with a continuous function. The molar Gibbs energy of that phase was expressed as the sum of two terms, one order-dependent and the other order-independent. Constraints between the parameters of the order-dependent term were required to ensure the stability of the disordered phase.