Mechanosynthesis of bcc alloys from Fe50−y/2Co50−y/2Sn y mixtures (2 ≤ y ≤ 33) and B2 ordering by annealing at modest temperatures
Résumé
Elemental powder mixtures of Fe, Co and Sn of initial compositions Fe 50-y/2 Co 50-y/2 Sn y (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 ~15 at.% in the dynamical conditions of milling which were selected. A recently discovered stannide, CoSn 5 , 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 119 Sn Mössbauer 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.
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