Фазовая диаграмма системы Au-Ni

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Au-Ni (Gold-Nickel) H. Okamoto and T.B. Massalski The equilibrium phases of the Au-Ni system are (1) the liquid, L, with a minimum freezing point of ~955 C at ~42.5 at.% Ni; and (2) the fcc continuous solid solution, with a miscibility gap at low temperatures. The critical point of the miscibility gap is at ~70.6 at.% Ni and 810.3 C. The assessed phase diagram is essentially the same as that of [Hansen]. Only the Cu-type fcc structure exists as the equilibrium state in the Au-Ni system. The liquidus and solidus are based on the thermodynamic model of [71Esd], with a minor modification. The calculated liquidus and solidus adequately represent the experimental phase boundaries [05Lev, 13Dec, 26Fra, 27Fra]. The incoherent (chemical or stable) miscibility gap has been investigated extensively. The assessed miscibility gap curve is based on the thermodynamic model of [71Esd]. The spinodal curve has also been calculated from the thermodynamic model of [71Esd]. Additional information on the coherent ( metastable) spinodal is available in [85Hof]. The observed large positive heat of mixing for the solid phase is in favor of clustering. However, [51Fli] reported that there was no tendency toward clustering in solid solutions in alloys containing 10 to 90 at.% Ni at 900 C, or in the same alloys quenched from 900 C, even though this temperature was only slightly above the miscibility gap. The same quenched alloys exhibited a preference for attraction between unlike neighbors, similar to the AuCu3-type short-range order. Alloys with 0.7, 1.12, and 1.72 at.% Au [59San1] and 3.2, 4.8, and 6.7 at.% Au [59San2] were found to consist of two phases at room temperature. Successive annealing at various temperatures generated various intermediate structures, including ordered Au3Ni, AuNi, and AuNi3. However, the low purity of the starting materials must be taken into consideration (99.9% Au, unknown Ni). A single-phase state was finally reached at a rather high temperature, above 900 C for the 0.7 at.% Au alloy. Similar transition structures were reported in alloys with 4.8, 6.7, and 8.4 at.% Au that were slowly cooled from 900 C to room temperature and then heated to various intermediate temperatures. A very small amount of C can stabilize metastable precipitated phases in a continuous solid solution phase field above the solvus. Thus, some of the reported metastable phases may be due to impurities in the specimens. Interdiffusion measurements in thin-film couples studied by [72Nen] showed no evidence of intermetallic compounds such as AuNi or Au3Ni. In the coherent miscibility gap, modulation of composition precipitation with a period of ~6.8 nm perpendicular to the <100> and <110> axes of the matrix was observed by [61Fuk] in an epitaxially grown 20 at.% Ni thin film homogenized in the continuous solid solution range and annealed to below 165 C. Similar modulation was observed in alloys with 15 to 80 at.% Ni. The Curie temperature (TC) trend of the Ni-rich solid solutions follows the approximate linear relationship 1450X - 1095.8 C (for X >> 0.5, where X is the atomic fraction of Ni in the alloys). The effect of the onset of ferromagnetism on the phase boundaries is expected to be negligible, because the compositions of the Au- and Ni-rich end of the miscibility gap below the apparent TC of the two-phase alloys are very close to 0 and 100 at.% Ni, respectively. The TC of pure Ni is 354.2 C. The apparent TC of alloys in the miscibility gap region is about 348.4 C. Editor's note: Unpublished data of [72Shr] on the solidus curve were re- evaluated by [88Hal]. The result agrees very well with the evaluated diagram. 05Lev: M. Levin, Z. Anorg. Chem., 45, 238-242 (1905) in German. 13Dec: P. De Cesaris, Gazz. Chim. Ital., 43(5), 609-620 (1913) in Italian. 26Fra: W. Fraenkel and A. Stern, Z. Anorg. Chem., 151, 105-108 (1926) in German. 27Fra: W. Fraenkel and A. Stern, Z. Anorg. Chem., 166, 161-164 (1927) in German. 51Fli: P.A. Flinn and B.L. Averbach, Phys. Rev., 83(5), 1070 (1951). 59San1: V.V. Sanadze and G.V. Gulyaev, Kristallografiya, 4(4), 526-533 (1959) in Russian; TR: Soviet. Phys. Crystallogr., 4(4), 496-502 (1960). 59San2: V.V. Sanadze and G.V. Gulyaev, Kristallografiya, 687-694 (1959) in Russian; TR: Soviet. Phys. Crystallogr., 4(5), 646-654 (1960). 61Fuk: Y. Fukano, J. Phys. Soc. Jpn., 16(6), 1195-1204 (1961). 71Esd: J.D. Esdaile and J.C.H. McAdam, Australas. Inst. Min. Met. Proc., (240), 103-112 (1971). 72Nen: T. Nenadovic, Z. Fotiric, B. Djuric, O. Nesic, T. Dimitrijevic, and R. Sofrenovic, Thin Solid Films, 12(2), 411-417 (1972). 72Shr: G.H. Shroff, M.S. thesis, Polytechnic Institute of Brooklyn (1972). 85Hof: F. Hofer and P. Warbichler, Z. Metallkd., 76(1), 11-15 (1985). 88Hal: T.A. Hall and A.A. Johnson, J. Less-Common Met., 141, L19-L22 (1988). Published in Phase Diagrams of Binary Gold Alloys, 1987. Complete evaluation contains 10 figures, 8 tables, and 101 references. 1