A study was made of the distribution of interstitial atoms in the octahedral sites of the face-centered-cubic austenite phase in the Fe-N system. The approach was based on the interplay between an analysis of Mössbauer data, Monte Carlo simulations, analytical calculations based on the quasichemical approximation to the statistical mechanics of interstitial solutions, and thermodynamic activity data. A database was developed, with analyses of Mössbauer spectra using models assuming either ordered or random distributions of the N atoms in the interstices around an Fe atom. The experimental trends were confronted with predictions of a combined theoretical approach. Thermodynamic activity data were analyzed, and the energies of the N-N pairs thus obtained were used in both Monte Carlo simulations and quasichemical approximation calculations, which were adopted as a suitable frame of reference for the critical comparison between the Fe-N and Fe-C systems. Monte Carlo predictions of the relative fractions of the Fe-N environment reveal that the consideration of only N-N interactions, as in the case of the Fe-C system, was not enough to describe the Fe-N austenite.

Distribution of Interstitial Atoms in FCC Fe-N Alloys: a Mössbauer, Thermodynamic and Monte Carlo Approach. L.Vergara, J.Desimoni, K.Laneri, A.Fernández Guillermet, G.J.Zarragoicoechea: Physica B, 2005, 363[1-4], 178-89