THE THERMODYNAMICS OF DILUTE TERNARY AUSTENITE SOLUTIONS

Abstract

A model based on nearest-neighbor interactions and regular behavior is used to calculate the thermodynamic activity of dilute ternary solutions of austenite (face-centered cubic iron) containing an interstitial and a substitutional component. The results, based on a standard state at infinite dilution, are[Formula: see text]and[Formula: see text]where N1and N2 are the mole fractions of the interstitial and substitutional solutes, respectively, and the [Formula: see text]'s are pair interaction energies. The symmetry relation existing between the coefficients in the above draws attention to a symmetry relation existing for an arbitrary empirical expansion of the activities for dilute solutions. The two-parameter relation for a1 accurately represents the data for Fe–C–Mn, Fe–C–Si, and Fe–C–Ni in the dilute range.