DISTRIBUTION OF CARBON ATOMS IN IRON-CARBON fcc PHASE: AN EXPERIMENTAL AND THEORETICAL STUDY

PHASE: AN EXPERIMENTAL AND THEORETICAL STUDY K. F. Laneri, J. Desimoni Departamento de F́ısica, Facultad de Ciencias. Exactas, UNLP, IFLP-CONICET C.C. 67, 1900 La Plata, Argentina G. J. Zarragoicoechea Instituto de F́ısica de Ĺıquidos y Sistemas Biológicos (CICPBA-UNLP) 59 No 789, C.C. 565, 1900 La Plata, Argentina A. Fernández-Guillermet Consejo Nacional de Investigaciones Cient́ıficas y Técnicas, Centro Atómico Bariloche, 8400 Bariloche, Argentina This paper presents an experimental and theoretical study of the distribution of carbon atoms in the octahedral interstitial sites of the face-centered cubic (fcc) phase of the iron-carbon system. The experimental part of the work consists of Mössbauer measurements in Fe-C alloys with up to about 12 atomic percent C, which are interpreted in terms of two alternative models for the distribution of C atoms in the interstitial sites. The theoretical part combines an analysis of the chemical potential of C based on the quasichemical approximation to the statistical mechanics of interstitial solutions, with three-dimensional Monte Carlo simulations. The latter were performed by assuming a gas like mixture of C atoms and vacancies (Va) in the octahedral interstitial sites. The number of C-C, C-Va and Va-Va pairs calculated using Monte Carlo simulations are compared with those given by the quasichemical model. Furthermore, the relative fraction of the various Fe environments were calculated and compared with those extracted from the Mössbauer spectra. The simulations reproduce remarkably well the relative fractions obtained assuming the Fe8C1−y model for Mössbauer spectra, which includes some blocking of the nearest neighbour interstitial sites by a C atom. With the