Фазовая диаграмма системы Cu-Ni

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Cu-Ni (Copper-Nickel) D.J. Chakrabarti, D.E. Laughlin, S.W. Chen, and Y.A. Chang The equilibrium phases in the Cu-Ni system are (1) the liquid phase, L, and (2) the (Cu,Ni) phase. The liquid phase is miscible in all proportions and is stable down to the melting point of Cu at 1084.87 C. (Cu,Ni) phase encounters phase separation at 354.5 C and 67.3 at.% Ni to form a1 and a2. At temperatures lower than TC, a2 changes from a paramagnetic to a ferromagnetic state. The phase equilibria below 354.5 C are calculated from a thermodynamic model. The accepted liquidus and solidus are based on [71Bas], [71Fee], and [71Sch] and on [Melt] for the melting points of Cu and Ni at 1084.87 and 1455 C, respectively. The phase diagram is also based on review of the pertinent experimental data [29Kru, 55Col, 57Mei, 62Rap, 64Sch, 68Lih, 68Moz, 69Elf, 71Pre, 72Tar, 78Vri]. No intermediate or ordered phases occur in the Cu-Ni system, contrary to the conflicting reports in the literature [Hansen]. High- pressure synthesis of any compound phase was not successful [Shunk]. A miscibility gap that closes at 177 C was predicted from thermodynamic analysis by [57Mei], based on an investigation of the ternary Cu-Ni-Cr system, in which a three-phase equilibrium among two fcc phases and a Cr-rich bcc phase was observed at 930 C. This phenomenon is unexpected, unless the binary Cu-Ni alloy exhibits a miscibility gap. [57Kos] observed a decrease in the electrical resistivity and Hall coefficient with alloys up to 45 at.% Ni on aging below 650 C. The minimum values in both the properties were reached at 450 C. Aging at elevated temperatures returned them to their former values. These changes were attributed to clustering in the alloys. [59Rya] subjected Cu-Ni alloys to neutron irradiation to improve the equilibrium distribution of atoms at low aging temperatures. Sharp increases in the magnetic susceptibility at temperatures approaching the Curie temperatures were observed in both 38.8 at.% Ni [58Pug] and 46.5 at.% Ni [ 59Rya] samples. The magnitudes of these increases could be accounted for only in terms of ferromagnetically coupled Ni-rich clustered regions. The evidence of cluster growth at room temperature in a 44 at.% Ni-Cu alloy was encountered by [74Leg]. After 3 years, they observed a marked change in the dependence of resistivity with temperature including the appearance of maxima and minima. Apparently, the initial quenching of the specimen from 1000 C introduced enough vacancies to promote clustering at room temperature. The removal of the resistivity peak on annealing at 800 C was attributed to the formation of random solid solution. [68Moz] made cluster diffuse neutron scattering measurements on a 47.5 at.% Ni sample and calculated the spinodal to be at 200 C and the miscibility gap maximum to occur at 310 C at 70 at.% Ni. They also predicted an asymmetric miscibility gap, which fell off more rapidly on the Ni-rich side than on the Cu-rich side of the diagram. [78Vri] calculated the detailed shape of the miscibility gap at various compositions (20 to 80 at.% Ni) from diffuse neutron scattering results and obtained the maximum at 65 at.% Ni between 340 and 350 C. In the assessed diagram, the miscibility gap has been calculated using thermodynamic data. In all previous phase diagram calculations, the magnetic term of the Gibbs energy for the fcc phase was not considered. Yet, with decreasing temperature, the magnetic term becomes increasingly important. In the present phase diagram calculation, both the chemical (nonmagnetic) and magnetic terms of the Gibbs energy are included. Data from [82Sha] were used. At 247.4 C, a metastable tricritical point exists, resulting in the formation of a metastable miscibility gap. With a decrease in temperature, the metastable phase boundary for the paramagnetic phase intercepts one branch of the spinodals (point b in the spinodal diagram), the phase boundaries b-c and b›-c› are then unstable. At c›, the ferromagnetic phase boundary intercepts the other branch of the spinodals. The boundaries then extend to lower temperature coinciding at d on the TC line. The same kind of equilibrium was found to occur in the bcc phase of (Fe,Cr) alloys. There is no direct experimental evidence to support the calculated miscibility gap. Attaining equilibrium condition at these low temperatures for these alloys is difficult, if not impossible. However, irradiation of these alloys at low temperatures may improve the kinetics of phase separation and offers the possibility of experimental verification of the calculated miscibility gap. Neutron scattering experiments by [69Hic] on weakly ferromagnetic Cu-Ni alloys (46 to 50 at.% Ni) near the critical composition (~44 at.% Ni) indicated the low-temperature spontaneous magnetization to be distributed in "magnetic polarization clouds extending over many atoms." Bulk magnetization measurements on 32 to 44 at.% Ni alloys showed that the polarization clouds with giant moments persisted well into the paramagnetic composition range [ 70Kou]. Direct measurement of the miscibility gap using normal metallographic methods is practically impossible, due to the slow kinetics of the decomposition process at these low temperatures. Some structural evidence for the presence of the gap was provided by the observations of spinodal decomposition [80Wag, 81Tsa, 81Wag]. [81Tsa] reported a spinodal temperature of 330 C for the Cu-45 at.% Ni alloy. [74Miy] obtained a modulated structure in a 60 at.% Ni alloy thin film after aging at 550 C. The latter work suggests that the gap is stable at much higher temperatures than heretofore reported. It is generally agreed that the magnetic clusters result from the chemical clustering of ferromagnetic Ni atoms. [71Bec] concluded that magnetic clusters in Cu-Ni alloys result from the clustering of Ni atoms, not from ordering. There remains an unresolved controversy about the temperature limits of stability of the gap. [72Mar] indicated the gap maximum to be at 500 C, based on cluster specific heat measurements on 40 at.% Ni, having extremely low magnetic impurities (<5 ppm Fe). [57Kos] and [79Not] also suggest similar high temperatures. On the other hand, the bulk of the other observations and the thermodynamic analysis in this evaluation indicate the maximum in the miscibility gap to lie below ~354.5 C. Ni and Ni-rich Cu-Ni alloys are ferromagnetic at low temperatures. The high-temperature equilibria between the liquid and vapor phase in Cu-Ni alloys were studied qualitatively by means of spectral analysis by [58Pal]. The results indicate a congruent point minimum near the middle of the diagram, with a very narrow two-phase field between the liquid and vapor phases. 29Kru: A. Krupkowski, Rev. Met., 26, 141, 153, 193-208 (1929) in French. 55Col: B.R. Coles, J. Inst. Met., 84, 346-348 (1955-1956). 57Kos: W. Koster and W. Schule, Z. Metallkd., 48, 592-594 (1957) in German. 57Mei: J.L. Meijering, Acta Metall., 5, 257-264 (1957). 58Pal: L.S. Palatnik, A.A. Levchenko, A.F. Bogdanova, and V.E. Terletskii, Fiz. Metal. Metalloved., 6(3), 540-544 (1958) in Russian; TR: Phys. Met. Metallogr. , 6(3), 153-157 (1958). 58Pug: E.W. Pugh and F.M. Ryan, Phys. Rev., 111(4), 1038-1042 (1958). 59Rya: F.M. Ryan, E.W. Pugh, and R. Smoluchowksi, Phys. Rev., 116, 1106-1112 ( 1959). 62Rap: R.A. Rapp and F. Maak, Acta Metall., 10, 63-69 (1962). 64Sch: C.W. Schultz, G.R. Zellars, S.L. Payne, and E.F. Foerster, U.S. Bur. Mines, Rept. Invest. 6410, 1-9 (1964). 68Lih: F. Lihl, H. Ebel, A. Reichl, and A. Kaminitschek, Z. Metallkd., 59, 735- 739 (1968) in German. 68Moz: B. Mozer, D.T. Keating, and S.C. Moss, Phys. Rev., 175, 868-876 (1968). 69Elf: L. Elford, F. Muller, and O. Kubaschewski, Ber. Bunsenges., 73, 601-605 (1969). 69Hic: T.J. Hicks, B. Rainford, J.S. Kouvel, and G.G. Low, Phys. Rev. Lett., 22, 531-534 (1969). 70Kou: J.S. Kouvel and J.B. Comly, Phys. Rev. Lett., 24, 598-601 (1970). 71Bas: B.D. Bastow and D.H. Kirkwood, J. Inst. Met., 99, 277-283 (1971). 71Bec: P.A. Beck, Met. Trans., 2, 2015-2024 (1971). 71Fee: E.A. Feest and R.D. Doherty, J. Inst. Met., 99, 102-103 (1971). 71Pre: B. Predel and R. Mohs, Arch. EisenhЃttenwes., 42, 575-579 (1971) in German. 71Sch: E. Schurmann and E. Schulz, Z. Metallkd., 62, 758-762 (1971) in German. 72Mar: D.L. Martin, Phys. Rev. B, 6, 1169-1176 (1972). 72Tar: S.K. Tarby, J.C. Bowker, and W.L. Stockdale, J. Inst. Met., 100, 374- 375 (1972). 74Leg: S. Legvold, D.T. Peterson, P. Burgardt, R.J. Hofer, B. Lundell, T.A. Vyrostek, and H. Gaertner, Phys. Rev. B, 9, 2386-2389 (1974). 74Miy: T. Miyazaki and H. Murayama, J. Jpn. Inst. Met., 38, 377 (1974) in Japanese. 78Vri: J. Vrijen and S. Radelaar, Phys. Rev. B, 17, 409-421 (1978). 79Not: M. Notin, G. Lefebvre, and J. Hertz, J. Solid State Chem., 28, 109-120 ( 1979) in French. 80Wag: W. Wagner, R. Poerschke, A. Axmann, and D. Schwahn, Phys. Rev. B, 21, 3087-3099 (1980). 81Tsa: T. Tsakalakos, Scr. Metall., 15, 255-258 (1981). 81Wag: W. Wagner, R. Poerschke, and H. Wollenberger, Philos. Mag. B, 43, 345- 355 (1981). 82Sha: R.C. Sharma, Trans. Ind. Inst. Met., 35, 372-375 (1982). Published in Phase Diagrams of Binary Nickel Alloys, 1991. Complete evaluation contains 8 figures, 6 tables, and 85 references. 1