A pair-interaction model for describing thermodynamic activities in binary ordered alloys with substitutional defects (antisite atoms) was formulated within the framework of the Bragg-Williams approximation, while taking the ordering energy to be the basic parameter. Analytical expressions were derived for the thermodynamic factor in chemical diffusion. The thermodynamic factor could be easily calculated by using the ordering energy which was obtained by analyzing activity data. Experimental data on thermodynamic activity in AgMg (B2), NiZr (L10) and Ni3Al were analyzed, and thermodynamic factor versus composition curves were derived.

A Bragg-Williams Model for the Thermodynamic Activity and the Thermodynamic Factor in Diffusion for Ordered Alloys with Substitutional Defects. T.Ikeda, H.Numakura, M.Koiwa: Acta Materialia, 1998, 46[18], 6605-13