The application of radiation diffuse scattering to the calculation of phase diagrams of F.C.C. substitutional alloys

Abstract

By using quantitative information about the radiation diffuse-scattering intensity of the disordered f.c.c. substitutional alloy the Fourier component of mixing energies of atoms may be estimated. We have to use the measurement data of the diffuse-scattering intensities at the corresponding reciprocal-space points k of the disordered phase and then determine the parameter w(k). The statistical thermodynamics of the nonideal solid solution is determined by these energy parameters {w(k)}. Therefore, one can obtain the configuration free energy of an alloy, F = U - TS (U - internal energy, S - entropy), and then determine its fundamental thermodynamic characteristics, including not only its phase diagram, but also the concentration-dependent order-disorder transformation temperature, temperature and concentration long-range order parameter dependences, chemical activity, heat capacity etc. Some thermodynamic properties are calculated within the framework of the statistical-thermodynamic approach for f.c.c.-Ni-Fe alloy. The diffuse-scattering intensity values are taken from data in the literature.