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hase Diagram Evaluations: Section II

Au-Fe-Sn (Gold-Iron-Tin) V. Raghavan

An isothermal section at 400 °C was determined for this system by Neumann et al. [1996Neu].

FeSn2. The first two phases decompose eutectoidally at 765 and 607 °C, respectively. FeSn and FeSn2 are stable at the temperature of interest here (400 °C).

Binary Systems Ternary Isothermal Section The Au-Fe binary diagram by [1993Oka1] depicts a peritectic reaction at 1173 °C between (␥Fe) and liquid containing 56.8 at.% Fe, which yields (Au) containing 74.1 at.% Fe. The Fe solubility in (Au) decreases with decreasing temperature reaching 9 at.% at 400 °C. The Au solubility in (␣Fe) is negligible at 400 °C. There are no intermediate phases in Au-Fe system. The update by [1993Oka2] of the Au-Sn system depicts a number of intermediate phases: Au10Sn (␤), ␨ (9.1-17.6 at. %Sn), ␨⬘ (Au5Sn), ␦ (AuSn), ␧ (AuSn2), and ␩ (AuSn4). For crystal structure data, see [Pearson3] or [1993Oka2]. Among these phases, ␤ (D024), ␨ (A3), and ␦ (B81) are stable at 400 °C. The Fe-Sn phase diagram [1993Oka3] depicts a miscibility gap in the liquid state and a ␥ loop at the Fe end. The intermediate phases are the hexagonal Ni2In-type Fe5Sn3, rhombohedral Fe3Sn2, hexagonal CoSn-type FeSn, and tetragonal CuAl2-type

With starting materials of 99.95% Au, 99.998% Fe and 99.98% Sn, [1996Neu] melted alloy compositions in evacuated silica tubes. The samples were annealed at 400 °C for 2-7 d and quenched in water. The phase equilibria were studied by metallography, x-ray powder diffraction and electron probe microanalysis. Differential thermal analysis measurements were also carried out between 20 and 1000 °C at a heating rate of 5 °C/min. The isothermal section at 400 °C determined by [1996Neu] is redrawn in Fig. 1 to agree with the accepted binary data. The solubility of Fe in ␤, ␨, and ␦ phases of the Au-Sn system is less than 2 at.%. The two liquid phases along the Au-Sn side dissolve not more than 2 at.% Fe. In FeSn and FeSn2 phases, less than 1 at.% Au dissolves [1996Neu]. The solubility of Au in Fe5Sn3 in the temperature range of its stability (765-910 °C) is not appreciable

Fig. 1 Au-Fe-Sn isothermal section at 400 °C [1996Neu]

Journal of Phase Equilibria and Diffusion Vol. 25 No. 1 2004

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Section II: Phase Diagram Evaluations [1996Neu]. No ternary phases were found in the system between 850 and 200 °C

1993Oka2: H. Okamoto: “Au-Sn (Gold-Tin),” J. Phase Equilibria, 1993, 14(6), pp. 765-66.

References

1993Oka3: H. Okamoto: “Fe-Sn (Iron-Tin)” in Phase Diagrams of Binary Iron Alloys, H. Okamoto, ed., ASM International, Material Park, OH, 1993, pp. 385-92.

1993Oka1: H. Okamoto, T.B. Massalski, L.J. Swartzendruber, and P.A. Beck: “Au-Fe (Gold-Iron)” in Phase Diagrams of Binary Iron Alloys, H. Okamoto, ed., ASM International, Materials Park, OH, 1993, pp. 33-40.

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1996Neu: A. Neumann, A. Kjekshus, and E. Rost: “The Ternary System Au-Fe-Sn,” J. Alloys Compd., 1996, 238, pp. 54-56.

Journal of Phase Equilibria and Diffusion Vol. 25 No. 1 2004