Фазовая диаграмма системы Au-Be

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Au-Be (Gold-Beryllium) H. Okamoto and T.B. Massalski The assessed Au-Be phase diagram is based mainly on thermal analysis data and the phase diagram by [38Win]. However, compared with the original diagram, the present phase boundaries have been drawn differently in several important details. A subregular solution model was employed in the present assessment to establish smooth and self-consistent liquidus boundaries. Based on the present thermodynamic model calculation derived from the phase boundary data of [38Win] , the L/[L + (Au)] liquidus boundary may involve an error of approximately с5 C. The equilibrium phases are (1) the liquid, L; (2) the fcc terminal solid solution, (Au); (3) the orthorhombic Au3Be phase, possibly unstable at low temperatures; (4) the tetragonal Au2Be phase; (5) the Au4Be3 phase, stable in the temperature range between 610 and 555 C; (6) the FeSi-type cubic phase aAuBe, with a high-temperature allotropic form, bAuBe; (7) the AuBe3 phase with a diamond-type structure; (8) the cubic AuBe5 phase; and (9) the bcc and cph terminal solid solutions, (bBe) and (aBe). The homogeneity ranges are mostly tentative and may need further investigation. The solubility of Be in (Au) is quite restricted [38Win, 45Owe]. Estimates based on lattice parameter measurements suggest a maximum solubility of ~0.2 at.% Be [49Cha, 62Cha]. The solubility of Au in (aBe) is about 0.25 at.% [49Cha, 62Cha] at 500 C. The temperature dependence of the solvus boundary is not known. [50Sid] reported a 2 to 3 at.% solubility range of Au in bBe, to which he ascribed a large hexagonal unit cell, which is not the accepted bBe (bcc) form. Therefore, this solubility feature is not included in the assessed diagram. [46Ray] theorized that a eutectic relation exists between the terminal solid solution of (aBe) and an intermediate phase (presumably AuBe5). 38Win: O. Winkler, Z. Metallkd., 30(5), 162-173 (1938) in German. 45Owe: E.A. Owen and E.A.O. Roberts, J. Inst. Met., 71, 213-254 (1954). 46Ray: G.V. Raynor, J. Roy. Aeronaut. Soc., 50, 390-415 (1946). 49Cha: G.P. Chatterjee and S.S. Sidhu, Phys. Rev., 76, 175 (1949). 50Sid: S.S. Sidhu and C.O. Henry, J. Appl. Phys. 21(10), 1036-1037 (1950). 62Cha: G.P. Chatterjee, J. Mines, Metals, Feuls (India), 10(6), 20-25 (1962). Published in Phase Diagrams of Binary Gold Alloys, 1987, and Phase Diagrams of Binary Beryllium Alloys, 1987. Complete evaluation contains 1 figure, 5 tables, and 23 references. Special Points of the Au-Be System