A semi-empirical parameterization of interatomic interactions based on the statistical-thermodynamic analysis of the data on radiation diffraction and phase equilibria in F.C.C.-Ni-Fe alloys

Using both the statistical-thermodynamics methods within the scope of the self-consistent field approximation and the diffraction data on coherent (or diffuse) scattering of X-rays (or thermal neutrons) from (dis)ordered f.c.c.-Ni-Fe alloys of various compositions, the estimation of interatomic interactions (including their magnetic contribution) and their temperature-concentration dependences were obtained. Based on the static concentration-wave representation, the expressions for configuration free energies of Ll2-Ni3Fe-type permalloy, L1 0-NiFe-type elinvar and Ll2-Fe3Ni-type invar were analyzed, considering explicit expressions for configuration entropies of atomic and magnetic subsystems with their configuration internal energies. Phase diagram of a system at issue was plotted within the field of the presence of f.c.c.-Ni-Fe alloys; their phase boundaries, equilibrium (static) properties near critical points (order parameter, etc.), and possible microstructures developed by composition-controlled magnetic transitions and/or order-disorder constant-composition solid-solid phase transformations were discussed. The obtained results were compared with available experimental data.