Фазовая диаграмма системы Au-Sm

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Au-Sm (Gold-Samarium) K.A. Gschneidner, Jr., F.W. Calderwood, H. Okamoto, and T.B. Massalski The Sm-Au system is characterized by the existence of eight compounds. The assessed phase diagram is based primarily on the work of [73Mcm]. The Sm-rich compound, Sm2Au, decomposes peritectically at 865 C to aSmAu and liquid. It crystallizes in the orthorhombic Co2Si-type structure [71Mcm]. SmAu melts congruently at 1525 C and is dimorphic; the a phase has the orthorhombic CrB-type structure and transforms at 1480 C to a b phase with the cubic CsCl-type structure [73Mcm]. [63Cha] obtained this structure only by the splat-cooling technique. The melting point of SmAu was reported to be 1525 C, and the a = b transformation was reported to occur at 1480 C [73Mcm]. [73Mcm] also reported the existence of a compound at about 53.8 at.% Au having the tentative stoichiometry Sm6Au7. The assessed phase diagram shows this compound and the associated phase boundaries as dashed lines with the assumed peritectic formation from SmAu and the melt at ~1170 C. [73Mcm] also reported the compound Sm7Au10 (58.8 at.% Au), which decomposes peritectically at 1105 C to Sm6Au7 and the melt. Weissenberg photographs showed this to be a bct structure. They found that SmAu6 decomposes peritectically at 800 C to Sm14Au51 and the melt. The Sm-rich eutectic composition is 19 at.% Au at 705 C. A eutectic between the compounds Sm7Au10 and SmAu2 occurs at 63.5 at.% Au and 1080 C. The eutectic between SmAu2 and SmAu3 occurs at 72 at.% Au and 1085 C. The eutectic between SmAu6 and Au was difficult to locate and was shown to occur at 770 C and 88.5 at.% Au [73Mcm]. The compound tentatively designated "Sm6Au7" and its associated phase boundaries are shown by dashed lines because of the uncertainty of its stoichiometry. The temperature for the b = g transformation in Sm has been lowered 2 C from the reported value of 924 C [73Mcm] to 922 C. The temperature for the metatectic reaction that results when Au is added to (Sm) has likewise been lowered 2 C from the reported value of 880 C [73Mcm] to 878 C. The sections of the liquidus not supported by differential thermal analysis data are shown as dashed lines. The maximum solubility of Sm in (Au) was determined by [65Rid] to be 0.3 at.%. [73Mcm] found the solubility of Au in (Sm) to be negligible. 63Cha: C.C. Chao, H.L. Luo, and P. Duwez, Jr., J. Appl. Phys., 34, 1971 (1963). 65Rid: P.E. Rider, K.A. Gschneidner, Jr., and O.D. McMasters, Trans. AIME, 233, 1488 (1965). 71Mcm: O.D. McMasters, K.A. Gschneidner, Jr., G. Bruzzone, and A. Palenzona, J. Less-Common Met., 25, 135 (1971). 73Mcm: O.D. McMasters and K.A. Gschneidner, Jr., J. Less-Common Met., 30, 325 ( 1973). Published in Phase Diagrams of Binary Gold Alloys, 1987. Complete evaluations contains 2 figures, 2 tables, and 10 references. 1