Interatomic Interactions in F.C.C.-Ni—Fe Alloys

Abstract

Within the scope of the self-consistent-field (SCF) and mean-SCF (MSCF) ap-proximations, static-concentration-waves and Matsubara—Kanzaki—Krivoglaz lattice statics methods, on the basis of state-of-the-art diffraction data con-cerning coherent and diffuse scattering of radiations in (dis)ordered f.c.c.-Ni— Fe alloys for various composition—temperature regions, and on the basis of data of independent magnetic measurements, the regular parameterization and estimation of ‘pair-wise’ interatomic interactions of the various nature (name-ly, ‘direct’ short-range ‘electrochemical’ and magnetic contributions as well as indirect long-range ‘strain-induced’ interaction) have been carried out taking into account their concentration and temperature dependences. As shown un-fortunately, many of available ‘electrochemical’ interaction parameters obtained with use of the well-known ab initio and semi-phenomenological compu-tational methodologies are limited in their applications for the statistical-thermodynamic analysis of f.c.c.-Ni—Fe alloys because most of them are con-trary to the regularities of a ‘mixing’-energy symmetry and, as a result, to the symmetries of observed L12-Ni3Fe-, L10-NiFe-or L12-Fe3Ni-type ordered phas-es. The ‘strain-induced’ interaction energy is anisotropic, long-range and qua-si-oscillating function of a distance between the solute atoms in a host crystal (throughout the temperature—concentration region of f.c.c.-Ni—Fe alloys). Combined ‘paramagnetic’ contribution to the ‘mixing’ energy depends implic-itly and essentially on concentration of Fe atoms, and its minimum Fourier-component values fall in the range of Invar compositions of Ni—Fe alloy. The temperature dependence of total ‘mixing’ energy is mainly due to the signifi-cant temperature-dependent magnetic contribution to it, and there is no need to take into account the effects of both substitutional correlations between atoms and many-particle interatomic-force interactions for characterization of microstructures developed by atomic ordering and (or) solid-phase precipita-tion in f.c.c.-Ni—Fe alloys. As expected, within the scope of the MSCF approx-imation, the estimated energy parameters of ‘exchange’ interactions in 1st co-ordination shell, JNiNi(rI) and JNiFe(rI), correspond to the ferromagnetic interaction between magnetic moments in Ni—Ni and Ni—Fe atomic pairs, and JFeFe(rI) corresponds to the antiferromagnetic interaction between magnetic moments in Fe—Fe atomic pairs.