Фазовая диаграмма системы Mg-Sn

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Mg-Sn (Magnesium-Tin) A.A. Nayeb-Hashemi and J.B. Clark Two eutectic reactions and a congruently melting line compound, Mg2Sn, characterize the Mg-Sn system. The phase diagram was originally determined by [ 05Gru] and [05Kur], and the assessed diagram is based primarily on their work, with modifications based on the work of [40Ray], [41Vos], [64Ste], [68Nay], [ 69Nay], and [73Ell]. The present authors have calculated the liquidus, assuming (Mg) to be a Raoultian solid solution, the heat of mixing to be independent of temperature, and nil solid solubility of Mg in (Sn). Despite a favorable size factor, the solubility of Sn in (Mg) is restricted by the formation of the stable Mg2Sn compound. The maximum solid solubility of Sn in (Mg) is 3.35 at.% Sn at 561.2 C. The maximum solid solubility of Mg in ( bSn) has not been determined, but appears to be infinitesimally small. A metastable phase has been reported in Sn-rich Mg-Sn alloys that were rapidly quenched from the melt to low temperatures. This metastable phase was unstable at room temperature and decomposed on heating at -100 to -40 C. The structure of the metastable phase at -190 C was found to be hexagonal. Formation of a metastable phase with the fcc structure was reported in splat- cooled Mg-rich Mg-Sn alloys. In a Mg-15 at.% Sn alloy, the lattice parameter of the metastable fcc phase was determined to be 0.4516 с 0.0009 nm at room temperature. This metastable phase decomposed at room temperature to the equilibrium phases. Another metastable phase was found on the Sn-rich side of the Mg2Sn compound. X-ray analysis of this phase produced diffraction pattern lines that were in fair agreement with those reported for a phase obtained in vapor-deposited films of a Mg-Sn alloy. This phase appeared to be metastable from room temperature to ~150 C for Mg-rich specimens and from room temperature to ~325 C for Sn-rich specimens. The cubic Mg2Sn, when exposed to temperatures of 600 to 1200 C and pressures of 2.5 to 5.5 GPa, transforms to a hexagonal structure [64Can]. This transformation occurs readily and at a faster rate above 770.5 C, the melting point of Mg2Sn at atmospheric pressure. Large grains of the new phase (hexagonal Mg2Sn) were formed on cooling. The temperature-pressure relationship of this transformation has been determined [ 72Dyu, 76Dyu]. The high-pressure structure can be preserved by quenching from a high temperature, followed by the release of pressure. 05Gru: G. Grube, Z. Anorg. Allg. Chem., 46, 76-84 (1905) in German. 05Kur: N.S. Kurnakow and N.J. Stepanow, Z. Anorg. Chem., 46, 177-192 (1905) in German. 40Ray: G.V. Raynor, J. Inst. Met., 6, 403-426 (1940). 41Vos: H. Vosskuhler, Metallwirtschaft, 20, 805-808 (1941) in German. 64Can: P. Cannon and E.T. Conlin, Science, 145, 487-489 (1964). 64Ste: A. Steiner, E. Miller, and K.L. Komarek, Trans. Metall. Soc. AIME, 230, 1361-1367 (1964). 68Nay: A.K. Nayak and W. Oelsen, Trans. Indian Inst. Met., 21, 15-20 (1968). 69Nay: A.K. Nayak and W. Oelsen, Trans. Indian Inst. Met., 22, 53-58 (1969). 72Dyu: T.I. Dyuzheva, S.S. Kabalkina, and L.F. Vereshchagin, Kristallografiya, 17(4), 804-811 (1972) in Russian; TR: Sov. Phys. Crystallogr., 17(4), 705-710 ( 1973). 73Ell: J. Ellmer, K.E. Hall, R.W. Kamphefner, J.T. Pfeifer, V. Stamboni, and C. D. Graham, Metall. Trans., 4, 889-891 (1973). 76Dyu: T.I. Dyuzheva, S.S. Kabalkina, and L.F. Vereshchagin, Proc. Akad. Nauk SSSR, 228(5), 1073-1075 (1976) in Russian. Published in Phase Diagrams of Binary Magnesium Alloys, 1988, and Bull. Alloy Phase Diagrams, 5(5), Oct 1984. Complete evaluation contains 2 figures, 15 tables, and 75 references. Special Points of the Mg-Sn System