Mechanosynthesis of bcc alloys from Fe 50− y /2 Co 50− y /2 Sn y mixtures (2 ≤ y ≤ 33) and B2 ordering by annealing at modest temperatures

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.