Фазовая диаграмма системы Cu-Ta

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Cu-Ta (Copper-Tantalum) P.R. Subramanian and D.E. Laughlin There is limited information on the phase relationships in the Cu-Ta system. The assessed Cu-Ta equilibrium diagram consists of the following equilibrium phases: (1) the liquid; (2) the fcc terminal solid solution (Cu), with limited solid solubility of Ta [36Dow]; and (3) the bcc terminal solid solution (Ta), with limited solid solubility of Cu. The assessed diagram is drawn from thermodynamic modeling [83Nie] based on the data of [59Smi] and [86Ver]. The diagram is in reasonable agreement with the prediction of [86Ver] and is characterized by an S-shaped near-flat liquidus above ~1800 C. This implies the existence of a metastable liquid-liquid miscibility gap at lower temperatures. This metastable miscibility gap is also included in the assessed diagram. It should be noted that the phase diagram for Cu-Ta is similar to that for Cu-Nb. This is understandable in view of the close resemblance between Ta and Nb with regard to occurrence and physical and chemical properties. The presence of interstitial impurities tends to stabilize the miscibility gap in the liquid; this has been observed in the case of the Cu-Nb [82Cha] and Cu-V [81Smi] systems. Although such an effect has not been reported for Cu-Ta, it seems reasonable to assume that the effects of impurities on phase equilibria in Cu-Ta are likely to be similar to those in Cu-Nb and Cu-V. This point should be given due consideration in future experimental determinations of the Cu-Ta phase equilibria. TEM and He+ ion channelling studies [78Cul] of specimens prepared by ion implantation of Ta into Cu thin films showed the formation of metastable substitutional solid solutions at low Ta implant concentrations. At higher implant concentrations (~10 at.% Ta), [78Cul] observed a transition from a crystalline to a noncrystalline form. Annealing of the different implanted Cu layers resulted in the restoration of equilibrium structures over different temperature ranges, although the noncrystalline form was observed to remain at temperatures close to 600 C. [85Nas] prepared amorphous thin films of Cu-Ta in the composition range 45 to 90 at.% Ta by coevaporation. TEM examination of the as-deposited specimens showed patterns corresponding to amorphous structures. However, Cu-rich specimens irradiated with a high dose of Xe ions (~13 displacements per atom) were observed to be partially decomposed to fcc Cu and a tetragonal form of Ta, referred to as bTa by [73Mos]. This tetragonal modification of Ta was observed in sputtered Ta thin films by [72Das] and in as-electrodeposited Ta from molten fluoride baths by [73Mos]. In situ annealing of the Cu-Ta films at 600 to 800 C resulted in the formation of crystalline structures corresponding to fcc Cu and tetragonal Ta for all compositions. 36Dow: A.G. Dowson, Dissertation abstract, Cambridge University, Cambridge, England (1936-1937); as quoted in [Hansen]. 59Smi: C.S. Smith, Trans. Metall. Soc. AIME, 215, 905-909 (1959). 72Das: G. Das, Thin Solid Films, 12, 305-311 (1972). 73Mos: P.T. Moseley and C.J. Seabrook, Acta Crystallogr. B, 29, 1170-1171 ( 1973). 78Cul: A.G. Cullis, J.A. Borders, J.K. Hirvonen, and J.M. Poate, Philos. Mag. B, 37(5), 615-630 (1978). 81Smi: J.F. Smith and O.N. Carlson, Bull. Alloy Phase Diagrams, 2(3), 348-351 ( 1981). 82Cha: D.J. Chakrabarti and D.E. Laughlin, Bull. Alloy Phase Diagrams, 2(4), 455-462 (1982). 83Nie: A.K. Niessen, F.R. de Boer, R. Boom, P.F. de Chatel, W.C.M. Mattens, and A.R. Midema, Calphad, 7(1), 51-70 (1983). 85Nas: M. Nastasi, F.W. Saris, L.S. Hung, and J.W. Meyer, J. Appl. Phys., 58(8) , 3052-3058 (1985). 86Ver: J.D. Verhoeven, F.A. Schmidt, E.D. Gibson, and W.A. Spitzig, J. Met., 38(9), 20-24 (1986). Published in Bull. Alloy Phase Diagrams, 10(6), Dec 1989. Complete evaluation contains 2 figures, 2 tables, and 17 references. 1