On the sublattice formalism applied to the B2 phase

The B2 phase disorders into the A2 phase. The thermodynamic behaviour of th ese two phases can be modelled by a two sublattice (SL) model. A new formul ation of this model, designated as modified sublattice (MSL) formalism, has been introduced to simplify its use to model order-disorder transformation s. The equations allowing the conversion of the SL model into the MSL forma lism are presented in the binary, ternary and quaternary cases. They show t hat some ordering parameters of the MSL are free and should not be used in an assessment procedure. Two practical cases of conversion, for the AI-NI a nd Ni-Ti systems, are discussed.