LOCAL INTERACTIONS IN CARBON-CARBON AND CARBON-M (M-AL, MN, NI) ATOMIC PAIRS IN FCC GAMMA-IRON

Mossbauer spectra of Fe-8.0 at.%C, Fe-10.9 at.%Al-8.2 at.%C, Fe-1.4at.%Mn7.9 at.%C, Fe-2.4at.%Mn-7.8 at.%C and Fe-14.6 at.%Ni-6.2 at.%C FCC gamma-irons have been measured in order to investigate the distribution and the local interactions of C in the lattice. The local interaction energies in nearest and second-nearest C-C and M-C (M: Al, Mn, Ni) atomic pairs have been determined by a Monte Carlo method simulating the distribution obtained. The interaction energies in nearest and second-nearest C-C pairs are strongly repulsive, in contrast to the weak interaction in second-nearest N-N pairs. The results are compared with the interaction energies derived from activity data. The interaction in nearest Al-C pairs is repulsive but that in second-nearest pairs is strongly attractive, which can lead to the formation of the perovskite Fe3AlC-type ordering. The interaction between nearest Mn and C atoms is strongly attractive, while between Ni and C the interaction is very weak.