Фазовая диаграмма системы Pd-Ti

К оглавлению: Другие диаграммы (Others phase diargams)

Pd-Ti (Palladium-Titanium) J.L. Murray The major phase diagram investigations of the entire composition range of the Ti-Pd system are [58Nis], [60Rud], [68Rau], and [72Ere]. [65Ros], [73Wil], [ 68Kra], and [79Eva] studied restricted composition and temperature regimes. There is no feature of this system about which all investigators agree. The number of observed intermetallic compounds has ranged from one [58Nis, 60 Rud] to eight [68Rau]. The early investigations of [58Nis] and [60Rud] are considered obsolete because of the impurity of the Ti used. In spite of many apparent difficulties noted in the literature, the assessed phase diagram represents a resolution of most of the conflicting reports. The partial phase diagram determinations of [73Wil], [65Ros], and [79Eva] resolved several discrepancies between [68Rau] and [72Ere]. Most of the conclusions of [72Ere] were corroborated by the independent work. However, some differences were irreconcilable, particularly for Pd-rich alloys, possibly because of the appearance of metastable precipitates. [68Rau] and [72Ere] measured the (bTi) solidus by thermal analysis and by the Pirani-Alterthum method, respectively. [72Ere] found a minimum in the solidus at 1120 C and between 30 and 35 at.% Pd. The maximum solubility of Pd in (bTi) was reported to be about 45 at.% Pd at 1310 C. [68Rau] reported that the solidus terminates at a eutectic point at 33 at.% Pd and 1140 C, with a maximum solubility of Pd in (bTi) of 31 at.% Pd. The congruent transformation of (bTi) to Ti2Pd is accepted, based on microstructural evidence. The assessed (aTi)/(bTi) boundaries are based on TEM and X-ray diffraction of [73Wil], who showed that optical microscopy is virtually useless for finding the eutectoid point. [68Rau] claimed that Ti3Pd5 rather than Ti2Pd3 should appear in the equilibrium diagram. [68Kra] made structure determinations of Ti2Pd3, Ti3Pd5, and two forms of TiPd2. The two TiPd2 phases and Ti3Pd5 have related structures. A thermal effect near 1280 C and a transformation microstructure demonstrated the existence of a polymorphic transformation of TiPd2 [72Ere]. A single TiPd2 phase field is shown with a dashed line at the temperature of the polymorphic transformation. Ti3Pd5 is also included, but equilibria with the other phases of the system are not known and therefore not indicated. [68Rau] proposed a cascade of peritectic reactions between the proposed (bTi) eutectic isotherm at 1280 C and a peritectic isotherm at 1390 C (L + TiPd3 = Ti3Pd5). [72Ere] proposed a eutectic reaction of Ti2Pd3 and aTiPd at 1280 C. As-cast microstructures of alloys in this composition range from both [68Rau] and [72Ere] show evidence of eutectic, which is not compatible with the diagram of [68Rau]. Therefore, the diagram of [72Ere] is tentatively accepted. [72Ere] reported that (Pd) melts congruently at 1400 C, and that the solubility of Ti in (Pd) is 22 at.%. [68Rau] showed a eutectic reaction at 1450 C with a solubility of 14 at.% Ti in (Pd). The congruent melting of (Pd) is accepted, on the basis of as-cast microstructures [58Nis, 72Ere, 68Rau]. [ 68Rau] observed superlattice lines of the ordered fcc L12 structure (g) in an 80 at.% Pd alloy; [79Eva] and [80Eva] verified the ordered structure. Alloys of less than 85 at.% Pd exhibited long-range order; alloys of less than 95 at.% Pd exhibited short-range order. The g phase may be a metastable phase that appears in supersaturated fcc (Pd) during quenching. If so, the equilibrium solubility of Ti in (Pd) is much more restricted than has been observed. The observed solubility is shown in the assessed diagram. The dot-dash line represents the composition beyond which ordering was observed. [77Cho] used Knudsen cell mass spectrometry to measure activities of Ti and Pd in Pd-rich liquid alloys at 1600 C. The derived excess Gibbs energies are extremely large. An incomplete diagram was calculated by [70Kau] in the regular-solution approximation, and more detailed calculations were performed as part of this evaluation. Present calculations in the subregular-solution approximation succeed in reproducing the liquidus and solidus curves of the solution phases. However, the observed diagram contains many features that are very implausible from the standpoint of thermodynamic modeling, and if one attempts to calculate the liquidus, these implausibilities are reflected in the Gibbs energies of the compounds. Both the thermodynamic quantities and the phase diagram require further experimental work before a reasonable calculation can be performed. 58Nis: H.Nishimura and T. Hiramatsu, Nippon Kinzoku Gakkai-shi, 22, 88-91 ( 1958) in Japanese. 60Rud: A.A. Rudnitskii and N.A. Birun, Zh. Neorg. Khim., 5(11), 2414-2421 ( 1960) in Russian; TR: Russ. J. Inorg. Chem., 5(11), 1169-1173 (1960). 65Ros: H.W. Rosenberg and D.B. Hunter, Trans. AIME, 233(4), 681-685 (1965). 68Kra: P. Krautwasser, S. Bhan, and K. Schubert, Z. Metallkd., 59(9), 724-729 ( 1968) in German. 68Rau: E. Raub and E. Roeschel, Z. Metallkd., 59(2), 112-114 (1968) in German. 70Kau: L. Kaufman and H. Bernstein, Computer Calculation of Phase Diagrams, Academic Press, New York (1970). 72Ere: V.N. Eremenko and T.D. Shtepa, Poroshk. Metall., (3), 75-81 (1972) in Russian; TR: Sov. Powder Metall. Met. Ceram., (3), 228-233 (1972). 73Wil: J.C. Williams, H.I. Aaronson, and B.S. Hickman, Metall. Trans., 4(4), 1181-1183 (1973). 77Cho: U.V. Choudary, K.A. Gingerich, and L.R. Cornell, Metall. Trans. A, 8A, 1487-1491 (1977). 79Eva: J. Evans and I.R. Harris, J. Less-Common Met., 64, P39-P57 (1979). 80Eva: J. Evans, I.R. Harris, and P.F. Martin, J. Less-Common Met., 75, P49- P53 (1980). Published in Phase Diagrams of Binary Titanium Alloys, 1987. Complete evaluation contains 4 figures, 5 tables, and 25 references. Special Points of the Ti-Pd System