Using first-principles quantum-mechanical theory, we demonstrate that the surface chemistry of Fe-Cr alloys follows the peculiar threshold behavior characteristic of ferritic stainless steels. We find that in dilute alloys the surfaces are covered exclusively by Fe, whereas for bulk Cr concentration above ϳ10% the Cr-containing surfaces become favorable. The two distinctly dissimilar surface regimes appear as a consequence of two competing magnetic effects: the magnetically induced immiscibility in bulk Fe-Cr alloys and the stability of magnetic surfaces.

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The elastic properties of ferromagnetic Fe 1−x M x ͑M = Al, Si, V, Cr, Mn, Co, Ni, and Rh; 0 Յ x Յ 0.1͒ random alloys in the body-centered-cubic ͑bcc͒ crystallographic phase have been studied using the all-electron exact muffin-tin orbitals method in combination with the coherent-potential approximation. The theoretical lattice parameters and the single-crystal elastic constants agree well with the available experimental data. The most significant alloying effects are found for Al, Si, and Ni additions. All elements enlarge the lattice parameter and decrease the C 11 , C 12 , and CЈ elastic constants and the bulk modulus of bcc Fe. At the same time, C 44 is found to increase with Al, Si, V, Cr, or Mn and remain nearly constant with Co, Ni, and Rh. Accordingly, the elastic anisotropy of bcc Fe increases with all alloying elements considered here. The calculated alloying effects on the single-crystal elastic constants are shown to originate from volume effects in combination with the peculiar electronic structure of bcc Fe.