Mechanosynthesis of bcc alloys from Fe50-y/2Co50-y/2Sny mixtures (2 ≤ y ≤ 33) and B2 ordering by annealing at modest temperatures

Elemental powder mixtures of Fe, Co and Sn of initial compositions Fe50-y/2Co50-y/2Sny(2 <= y <= 26) are ball-milled at high-energy. They yield metastable alloys which are predominantly composed of a supersaturated bcc Fe-Co-Sn phase. The amount of tin dissolved in it is at least (similar to)15 at.% in the dynamical conditions of milling which were selected. A recently discovered stannide, CoSn5, passed hitherto unobserved in Co-Sn binary phase diagrams. It forms at Co-Sn interfaces at very short milling times, 0.5h, thanks to the high-diffusivity of cobalt in tin. Finally, neutron diffraction and Sn-119 Mossbauer spectroscopy show that metastable B2 ordering develops in as-milled alloys, for y <= 26, when they are further annealed at modest temperature, here for 15h at 675K. The tendency to long-range order in ternary Fe-Co-Sn bcc alloys is thus observed in metastable alloys.