Фазовая диаграмма системы Au-Fe

К оглавлению: Другие диаграммы (Others phase diargams)


Au-Fe (Gold-Iron) H. Okamoto, T.B. Massalski, L.J. Swartzendruber, and P.A. Beck The equilibrium phases of the Au-Fe system are (1) the liquid, L; (2) the fcc terminal solid solution, (Au); (3) the terminal solid solution based on the high-temperature bcc phase of Fe, (dFe); (4) the terminal solid solution based on the fcc phase of Fe, (gFe); and (5) the terminal solid solution based on the low-temperature bcc phase of Fe, (aFe). The general forms of the liquidus and solidus were established by [07Isa] via thermal analysis. Subsequently, the L/[L + (gFe)] and L/[L + (Au)] liquidus and [L + (Au)]/(Au) solidus boundaries were measured primarily by [50Rau] and [ 63Buc] with thermal analysis. The [L + (dFe)]/(dFe) solidus and solubility limits of (Au), (aFe), and (gFe) were determined from lattice parameter measurements. The present phase diagram has been assessed with the aid of a thermodynamic model. Earlier, the existence of the AuFe3 and AuFe15 phases and a congruent minimum in the (gFe) <259> (aFe) transformation temperature were suggested, but these features have not been confirmed. Agreement between the experimental data and the thermodynamic calculation is generally excellent. Below 800 C, the data points for the (Au)/[(Au) + (gFe)] boundary tend to fall on or below the metastable extension of the fcc phase miscibility gap. Alloys with 45 to 90 at.% Fe can be made amorphous when thin films are deposited on a substrate maintained at liquid hydrogen temperature. These amorphous alloys always crystallized below the ambient temperature. Amorphous films with 60 to 80 at.% Fe were prepared by vapor deposition on a substrate held at the liquid nitrogen temperature. Electron microscopic observations showed that the resulting crystal structures are fcc for alloys with less than 62 at.% Fe and bcc for alloys with more than 62 at.% Fe. These structures are not the same as those found in the assessed phase diagram. The fcc solid solutions, (Au) and (gFe), are stable at elevated temperatures, but they can be retained by quenching to room temperature. Early magnetic measurements showed that the metastable solid solutions, as quenched, are quite stable, even at an Fe concentration as high as 35 at.%; no detectable bcc (aFe) precipitation takes place at least up to 200 h at 200 C or 450 h at 50 C. A gradual increase in the susceptibility with time at aging temperatures, ranging from 20 to 200 C, showed the occurrence of a pre- precipitation aging effect. The Curie temperature in the (aFe) phase was shown to be nearly independent of Au concentration. 07Isa: E. Isaak and G. Tammann, Z. Anorg. Allg. Chem., 53, 281-297 (1907) in German. 50Rau: E. Raub and P. Walter, Z. Metallkd., 41(8), 234-238 (1950) in German. 63Buc: R.A. Buckley and W. Hume-Rothery, J. Iron Steel Inst. (London), 201, 121-124 (1963). 75Mar: G. Marchal, Ph. Mangin, and C. Janot, J. Phys. (Paris), 36(C2), 91-95 ( 1975). Published in Phase Diagrams of Binary Gold Alloys, 1987, and Bull. Alloy Phase Diagrams, 5(6), Dec 1984. Complete evaluation contains 3 figures, 9 tables, and 96 references. Special Points of the Au-Fe System