Фазовая диаграмма системы Au-Mn

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Au-Mn (Gold-Manganese) T.B. Massalski and H. Okamoto The tentative equilibrium phases of the Au-Mn system are (1) the liquid, L; (2) the fcc terminal solid solution, (Au), with a maximum solid solubility of 31 at.% Mn in (Au); (3) the terminal solid solutions-(dMn), (gMn), (bMn), and ( aMn)-based on the four allotropic forms of Mn, with maximum solid solubility of 25 at.% Au in the fcc (gMn), and with very small (<1 at.%) solubility of Au in the other forms of (Mn); (4) several intermediate phases-Au4Mn (a›), a››, Au33Mn9, Au31Mn9, lozenge-shaped island structures, Au13Mn4 (h), Au3Mn, Au11Mn4 (X), Au5Mn2, and Au2Mn- in the composition range between ~17 at.% Mn and 33.3 at.% Mn; (5) the CsCl-type cubic intermediate phase AuMn (b phase) with the congruent melting point at 1260 C and a homogeneity range from 33.4 to 69.2 at.% Mn, and three low-temperature allotropic forms of the b phase, b›1, b1, and b2; and (6) the MoSi2-type tetragonal intermetallic phase AuMn2, having no apparent solubility range. Although several contradictory phase diagrams have been proposed for the Au-Mn system, the assessed phase diagram is based primarily on the work of [53Rau], with updates resulting from recent experimental and theoretical work. The liquidus and solidus boundaries related to the fcc phases were obtained by thermodynamic modeling. The partial diagram between 15 and 30 at.% Mn of [ 64Kos] has been accepted along the boundaries between (Au) and several compounds (15 to 25 at.% Ni). All the possible phases in the Au-Mn system are included in the assessed diagram, although some may be metastable or stable only in thin films. The a›› phase has a composition range of 21.2 to 22 at.% Mn. The high- temperature limit is 525 C at 22 at.% Mn. At 21 at.% Mn, this phase was reported to change to the tetragonal a› below about 400 C [62Mor]. A stable orthorhombic phase, Au13Mn4, based on a cph stacking, occurs at 23.53 at.% Mn and is stable below 625 C [79Ten]. Antiphase modulations, stacking fault modulations, and continuous modulations of the D022 structure were proposed as an explanation of the various phases in the composition range between 20 and 28 at.% Mn. However, the boundaries between these phases are not well defined. In X-ray studies on specimens quenched from annealing temperatures below ~615 C, the b1 phase with c/a < 1 was observed in alloys with less than 50 at.% Mn, and the b2 phase with c/a > 1 was observed in alloys with more than 50 at.% Mn [53Rau]. [56Kus] reported that the b <259> b1, b2 transformation temperature is slightly above 640 C. No two-phase field was detected between b1 and b2. The b1 phase has been subdivided into b<291>1 and b1, where the b <259> b<291> 1 transition corresponds to the structure change due to the onset of antiferromagnetism in the b phase. The b<291>1 <259> b1 and b‚1 Ћ b2 transitions correspond to other martensitic phase transformations. A transitional phase Au3Mn(I) with an orthorhombic fundamental cell forms when a 25 at.% Mn alloy is cooled from the disordered (Au) phase [63Mor]. The fcc ( gMn) solid solution is reported to transform on quenching to a tetragonal lattice in alloys with less than 5 at.% Au [53Rau]. The transition temperature from the metastable (gMn) phase to the metastable fct phase gMn1 (c/a < 1) corresponds to the N‚el temperature [80Har]. 53Rau: E. Raub, U. Zwicker, and H. Baur, Z. Metallkd., 44(7), 312-320 (1953) in German. 56Kus: A. Kussmann and E. Raub, Z. Metallkd., 47(1), 9-15 (1956) in German. 62Mor: D.P. Morris and J.L. Hughes, Acta Crystallogr., 15, 1062 (1962). 63Mor: D.P. Morris, J.L. Hughes, and G. Davies, Philos. Mag., 8(95), 1977-1980 (1963). 64Kos: W. Koster and R.E. Hummel, Z. Metallkd., 55(4), 175-179 (1964) in German. 79Ten: G. Van Tendeloo, M. Van Sande, and S. Amelinckx, Phys. Status Solidi, A, 55(2), 681-689 (1979). 80Har: T.M. Harders, J.H. Smith, and E.R. Vance, J. Magn. Mater., 15-18(3), 1177-1178 (1980). Published in Phase Diagrams of Binary Gold Alloys, 1987, and Bull. Alloy Phase Diagrams, 6(5), Oct 1985. Complete evaluation contains 5 figures, 5 tables, and 121 references. Special Points of the Au-Mn System