First-principles study of stability and local order in bcc-based Fe-Cr and Fe-V alloys

A parameter-free approach is applied to the study of the electronic structure properties and the local chemical order in Fe-Cr and Fe-V alloys. The method is based on a multiple-scattering description of the electronic-structure properties of the random alloys. Configurational order is treated within the generalized perturbation method, and temperature effects are examined with standard statistical methods, namely, the cluster-variation method and Monte Carlo simulations. In reasonable agreement with experiments, FeV exhibits a tendency toward order with a B2 superstructure in contrast to FeCr which shows an overall tendency toward phase separation around equiatomic composition. A more detailed study is performed for Fe-Cr alloys as a function of temperature and concentration, in the light of recent diffuse-scattering experiments. Finally, some conclusions are drawn regarding the structural transformation which occurs in both alloys from the bcc solid solution to a complex Frank-Kasper phase upon cooling.