Phase equilibria in the ternary Ni-Sb-Sn system: Experiments and calculations

The ternary Ni-Sb-Sn phase diagram was investigated experimentally by a combination of powder X-ray diffraction (XRD), electron probe microanalysis (EPMA), scanning electron microscopy (SEM), and differential thermal analysis (DTA). Ternary phase equilibria were experimentally evaluated for four partial isothermal sections at 1000, 900, and 500°C (for the Ni-rich part) and at 400°C (for the Sb/Sn-rich part) of the system. A continuous solid solution between the two B8-type phases Ni ₃Sn ₂ HT(ζ) and NiSb was observed. Although it cannot be proved unequivocally that a similar continuous solid solution exists between the two D0 ₃-type phases Ni ₃Sn HT and β-Ni ₃Sb (since neither the two binary phases nor any possible ternary solid solution can be retained on quenching) the experimental results suggest indirectly such a continuous solution. The solubility ranges of all other binary phases were determined. The ternary skutterudite-type phase Sn _yNi ₄Sb _12-xSn _x was found to decompose in a ternary peritectic reaction at about 485±5°C. The experimental results, together with additional available literature information, were used to perform a thermodynamic assessment of the ternary system. Five calculated isothermal sections (1000, 900, 500, 400, and 250°C) and three isopleths (x _Ni/x _Sn=3/1, 3/2, and 3/4) are presented, together with a Scheil reaction scheme and a liquidus projection for the entire ternary Ni-Sb-Sn system.