Фазовая диаграмма системы Nb-Pd

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Nb-Pd (Niobium-Palladium) M.S. Chandrasekharaiah The Nb-Pd phase diagram is known with reasonable accuracy. [61Sav] and [80Gie] studied the phase diagram over the entire composition range. However, the limited number of compositions investigated and the uncertain purity of the samples used rendered the results of [61Sav] less reliable. Therefore, the equilibrium diagram is based primarily on [80Gie]. Based on the available data, the equilibrium phases of the Nb-Pd system are accepted as (1) the liquid, L; (2) the bcc solid solution, (Nb), with up to 36 at.% solid solubility of Pd; (3) the fcc solid solution, (Pd), with 30 at.% solid solubility of Nb; (4) NbPd, with a high-temperature disordered Cu-type structure, stable between 1565 and 1255 C, exhibiting homogeneity of 49 to 60 at.% Pd at the high-temperature end; (5) NbPd2, an orthorhombic MoPt2-type phase, with a very narrow homogeneity range (between 66 and 67 at.% Pd); and ( 6) two NdPd3 phases--low-temperature aNbPd3 with bct Al3Ti-type structure, and orthorhombic bNbPd3, formed from (Pd) through a eutectoid reaction at 1560 C. The two forms are related structurally. The phase transformation between them is not fully established. The liquidus boundary, especially on the Nb-rich side of the diagram, has not been accurately determined and therefore is shown by a dashed line. Both terminal solid solution phases exhibit considerable solid solubility [ 61Sav, 80Gie]. The bcc (Nb) phase dissolves up to 36 at.% Pd at the eutectic temperature of 1520 C, but the solubility decreases with the lowering of the temperature, especially below 1255 C. Solubility is only ~20 at.% Pd at 800 C. The fcc (Pd) phase dissolves about 31 at.% Nb at 1610 C, but this solubility decreases to about 18 at.% Nb at 1500 C and remains almost constant below this temperature. (Pd) exhibits a congruent melting maximum at 1625 C and 75 at.% Pd. 61Dwi: A.E. Dwight, Columbium Metallurgy, Proc. TMS-AIME Conf. 1961, Vol. 10, 384-406 (1961). 61Sav: E.M. Savitskii, V.V. Baron, and A.N. Kotinskayo, Zh. Neorg. Khim., 6, 2603-2605 (1961). 64Gie: B.C. Giessen and N.J. Grant, Acta Crystallogr., 17, 615-616 (1964). 65Gie: B.C. Giessen and N.J. Grant, J. Less-Common Met., 8, 114-119 (1965). 72Pea: W.B. Pearson, The Crystal Chemistry and Physics of Metals and Alloys, John Wiley, New York, 330-331 (1972). 80Gie: B.C. Giessen, N.J. Grant, D.P. Parker, R.C. Manuszewski, and R.M. Waterstrat, Metall. Trans. A, 11, 709-715 (1980). Published in Bull. Alloy Phase Diagrams, 9(4), Aug 1988. Complete evaluation contains 1 figure, 3 tables, and 15 references. Special Points of the Nb-Pd System