Фазовая диаграмма системы Au-Cu

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Au-Cu (Gold-Copper) H. Okamoto, D.J. Chakrabarti, D.E. Laughlin, and T.B. Massalski The Au-Cu system is one of the earliest systems for which several order- disorder type transformations were established. Although a very large volume of work exists on the ordered AuCu and AuCu3 phases, only limited phase diagram details for the Au-Cu system have been generated during the past two decades. The assessed phase diagram is based on review of the experimental phase diagram data [00Rob, 07Kur, 34Bro, 62Ben, 64Zai], and was obtained by thermodynamic modeling. The system is characterized by a continuous solid solution phase below the solidus. The liquidus and solidus boundaries established by [62Ben], who used cooling and heating curves (~2 to 3 C/min), and whose experimental work appears to be the most reliable, are accepted in the assessed diagram. The decrease in the melting temperature of Cu with additions of Au (up to 3.3 at.%) determined by [ 1897Hey] is also consistent with the presently accepted liquidus. The liquidus in the assessed diagram can also be derived from the present thermodynamic assessment, which is consistent with the reported thermodynamic quantities. The solidus temperatures of [62Ben] are lower than the calculated values (maximum difference ~10 C) in the composition range ~80 to 90 at.% Cu, where the actual thermodynamic properties may be slightly different from the model properties. The experimental phase boundary data related to the ordered Au3Cu phase have been reported as various values by different investigators, presumably because of the difficulty in attaining a full equilibrium state at low transformation temperatures (<240 C). Most of the presently assessed phase boundaries are based on the isothermal change in the electrical resistivity measured by [55Rhi], [59Hir], and [59Kor]. The occurrence of compound-like phases at the AuCu and the AuCu3 stoichiometric compositions was first observed by [15Kur], who employed thermal analysis, hardness, and X-ray measurements. [23Bail], [23Bai2], and [ 23Bai3] associated the occurrence of atomic ordering with these compounds on the basis of observed X-ray diffraction lines. [36Joh] discovered an additional order-order transformation in AuCu at higher temperatures, in which an orthorhombic AuCu(II) phase forms from the tetragonal AuCu(I) phase. Prior to this, AuCu(I) was thought to transform directly to the disordered fcc phase (AuCu(D)) at higher temperatures. Detailed phase boundary determinations, including the indications of congruent transformations at AuCu3 and AuCu compositions, were made by [31Gru] and [ 31Hau]. They also correctly indicated the existence of two-phase fields between the ordered and disordered phases. A third low-temperature phase with an extended phase field that included the stoichiometry Au3Cu was reported to form peritectoidally by [31Gru]. [53New], [53Rhi], [54New1], and [55Rhi] defined precise boundaries for the different phase fields and confirmed the congruent formation of AuCu and AuCu3 and the peritectoidal formation of Au3Cu. The assessed diagram is based primarily on [55Rhi], [57Pia], and [59Pia1] for the high-temperature boundaries and on [57Pia] for the AuCu(II) = AuCu(I) boundaries, for which [55Rhi] did not present any data. The AuCu(D) = AuCu(II) transformation temperature is accepted as 410 с 2 C. The AuCu(II) = AuCu(I) temperature is accepted as 385 с 2 C based on [73Bar] and [73Gol]. The existence of a two-phase field between AuCu3 and AuCu(I), from 34 to 37 at. % Au, and the associated eutectoid decomposition of the fcc solid solution was proposed by [31Gru]. [55Rhi] confirmed the eutectoid transformation of (Cu, Au) and precisely determined the eutectoid point to lie at 36 at.% Au and at 284 C. The accepted AuCu3(I) phase boundaries are based primarily on [55Rhi]. [54New2] confirmed that a two-phase field occurs not only on the Au-rich side of the AuCu3 composition, but also on the Cu-rich side. The AuCu3(I) phase is stable over wide composition limits on both sides of the stoichiometric point. It forms from the disordered phase by a congruent transformation at the stoichiometric composition and at Au-rich limits by a eutectoid transformation. The congruent and eutectoid temperatures at 390 and 284 C, respectively, and the eutectoid composition at 36 at.% Au are accepted from [55Rhi] as being the most precise. By analogy with the occurrence of the AuCu(II) structure, [60Sco] proposed that a one-dimensional long-period superlattice (LPS) structure, designated AuCu3(II), occurs at Au-rich off-stoichiometric compositions. The narrow single-phase field was shown to lie inside the (Cu, Au) and AuCu3(I) two-phase field, and the likely boundaries were also proposed [60Sco, 74Per]. According to [80Wil], the AuCu3(II) phase does not exist. The existence of a two-phase mixture of AuCu3(I) and a disordered Au-Cu solid solution is sufficient to explain the scattering phenomenon usually associated with the AuCu3(II) LPS [80Wil]. This is an interesting suggestion, but experimental observation of the disordered regions must be presented before the LPS structure is rejected. The long-period superlattice structure [62Sat, 66Tac1, 66Tac2] is associated with a particular energy band structure of conduction electrons that can be altered by pressure. The AuCu(II) = AuCu(I) transition temperature was found to increase with the measured pressure, up to 70 kbar, at the rate of 1.5 с 0. 2 C/kbar by [72Iwa] and [74Iwa]. Above 50 kbar, the AuCu(II) structure disappeared and only the ordered structure AuCu(I) was present. [75Asa] observed the transition temperature to increase with pressure at the rate of 2.0 C/kbar, which compares well with the theoretically predicted rate of 1.95 C/kbar, as derived from the Clausius-Clapeyron equation [74Iwa]. Measurements extended to 100 kbar using electrical resistivity showed a linear relation between pressure and the transition temperature. 1897Hey: C.T. Heycock and F.H. Neville, Philos. Trans. R. Soc. (London) A, 189, 25-69 (1897). 00Rob: W.C. Roberts-Austen and T.K. Rose, Proc. R. Soc. (London) A, 67, 105- 112 (1900). 07Kur: N.S. Kurnakov and S.F..Zemczuzny, Zh. Russ. Fiz-Khim. Obshchestva, 39, 211-219 (1907) in Russian; TR: Z. Anorg. Chem, 54, 149-169 (1907) in German. 15Kur: N.S. Kurnakov, S.F. Zemczuzny, and M. Zasedatelev, Zh. Russ. Fiz-Khim. Obshchestva, 47, 871-897 (1915) Russian; TR: J. Inst. Met., 15, 305-331 (1916). 23Bai1: E.C. Bain, Chem. Met. Eng., 28, 21-24 (1923). 23Bai2: E.C. Bain, Chem. Met. Eng., 28, 67-68 (1923). 23Bai3: E.C. Bain, Trans. 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Goddard, Acta Metall., 7(12), 757-761 (1959). 60Fli: P.A. Flinn, G.M. McManus, and J.A. Rayne, J. Phys. Chem. Sol., 15, 189- 195 (1960). 60Sco: R.E. Scott, J. Appl. Phys., 31, 2112-2117 (1960). 62Ben: H.E. Bennett, J. Inst. Met., 91, 158 (1962-1963). 62Sat: K. Sato, D. Watanabe, and S. Ogawa, J. Phys. Soc. Jpn., 17(10), 1647- 1651 (1962). 64Zai: S.A. Zaitseva and Yu.A. Priselkov, Vestn. Mosk. Univ., Ser. II, Khim., 19(6), 22-23 (1964) in Russian. 66Lul: S.S. Lu and C.K. Liang, K'o Hsueh T'ung Pao, 17(9), 395-396 (1966) in Chinese. 66Lu2: S.S. Lu and C.K. Liang, K'o Hsueh T'ung Pao, 17(11), 495-496 (1966) in Chinese. 66Tac1: M. Tachiki and K. Teramoto, J. Phys. Chem. Sol., 27(2), 335-348 (1966). 66Tac2: M. Tachiki, Phys. Rev., 150(2), 440-447 (1966). 67Bje: E. Bjerkelund, W.B. Pearson, K. Selte, and A. Kjekshus, Acta Chem. Scand., 21(10), 2900-2902 (1967). 68Oka: K. Okamura, H. Iwasaki, and S. Ogawa, J. Phys. Soc. Jpn., 24(3), 569- 579 (1968). 72Iwa: H. Iwasaki, J. Phys. Soc. Jpn., 33(6), 1721 (1972). 73Bar: R.D. Barnard and A.J.M. Chivers, Metal. Sci. J., 7, 147-152 (1973). 73Gol: N.S. Golosov, L.E. Popov, and L.Ya. Pudan, J. Phys. Chem. Sol., 34(7), 1149-1163 (1973). 74Iwa: H. Iwasaki, H. Yoshida, and S. Ogawa, J. Phys. Soc. Jpn., 36(4), 1037- 1042 (1974). 74Per: G. van der Perre, H. Goeminne, R. Geerts, and J. van der Planken, Acta Metall., 22(2), 227-237 (1974). 75Asa: K. Asaumi, Jpn. J. Appl. Phys., 14(3), 336-340 (1975). 80Wil: R.O. Williams, Metall. Trans. A, 11(2), 247-253 (1980). Published in Phase Diagrams of Binary Gold Alloys, 1987, and Bull. Alloy Phase Diagrams, 8(5), Oct 1987. Complete evaluation contains 13 figures, 9 tables, and 258 references. 1