Application of the cluster variation method to ordering in an interstitital solid solution: the gamma-Fe[N]/gamma'-Fesub4Nsub1-x equilibrium

The tetrahedron approximation of the cluster variation method (CVM) was applied to describe the ordering on the fcc interstitial sublattice of gamma-Fe[N] and gamma'-Fe4N1-x. A Lennard-Jones potential was used to describe the dominantly strain-induced interactions, caused by misfitting of the N atoms in the interstitial octahedral sites.

The gamma-Fe[N]/gamma'-Fe4N1-x miscibility gap, short range ordering (SRO), and long-range ordering (LRO) of nitrogen in gamma-Fe[N] and gamma'-Fe4N1-x, respectively, and lattice parameters of gamma and gamm' were calculated. For the first time, N distribution parameters,as calculated by CVM, were compared directly to Mössbauer data for specific surroundings of Fe atoms.