Фазовая диаграмма системы Hf-Zr

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Hf-Zr (Hafnium-Zirconium) J.P. Abriata, J.S. Bolcich, and H.A. Peretti There is general agreement [69Rud, Elliot, Hafnium, Hansen, Zirconium] regarding the main features of the Zr-Hf phase diagram. In the liquid phase, there is complete misicibility. In the solid state, high-temperature bcc (b) phase and a low-temperature cph (a) phase exist. Both phases extend from 0 to 100% Hf. The a = b and b = L equilibrium transformations are incongruent for all alloy compositions. It is generally accepted that the Zr-Hf phase diagram corresponds to the situation of nearly ideal solutions. The temperatures accepted in the present diagram for the a/b equilibrium in pure Zr and pure Hf are 863 C [Zirconium] and 1743 C [Hafnium], respectively. The assessed (a + b) boundaries are a compromise between the indicated allotropic transformation temperatures of the pure metals and the alloy experimental data of [57Hay] and [66Dom]. Considerable uncertainty exists regarding the shape (width) of the provisional (a + b) region. The melting points of Zr and Hf have been accepted as 1855 and 2231 C, respectively [Melt]. The solidus has been adjusted to the values given by [57Hay], and the calculated liquidus agrees well with the experimental data of [57Hay]. Three allotropic solid phases exist in pure Zr and Zr-Hf alloys under pressure: a, b and w (hexagonal). This also appears to be true for pure Hf. Usually, strong hysteresis effects are observed in the a <259> w transition pressures at room temperature. The experimentally observed pressures at which the a <259> w transformation occurs appear to be much higher than the estimated equilibrium values. For pure Hf, the predicted value based on experimental work is about 600 kbar at room temperature [81Min], compared with an estimated value of 210 kbar [75Kut]. Phenomenological modeling of the Zr-Hf phase diagram frequently has been based on the assumption of ideal behavior of the phases involved. This assumption is consistent with the fact that the volume of formation of Zr-Hf alloys can be assessed to be essentially zero for all compositions and, more generally, with the observation that there are very close similarities between the physicochemical properties of the group IV transition elements Zr and Hf. 57Hay: E.T. Hayes and D.K. Deardorff, U.S. At. Energy Comm. USBM-U-345 (Aug 1957); cited in D.K. Deardorff, O.N. Carlson, and H. Kato, The Metallurgy of Hafnium, D.E. Thomas and E.T. Hayes, Ed., U.S. Atomic Energy Commission, 191- 210 (1960). 66Dom: R.F. Domagala, J. Less-Common Met., 11, 70 (1966). 69Rud: E. Rudy, Compendium of Phase Diagram Data, AFML-TR-65-2, Part V, Air Force Materials Laboratory, Metals and Ceramics Division, Wright-Patterson Air Force Base, OH, 73 (1969). 75Kut: A.R. Kutsar, Fiz. Met. Metalloved., 40, 786 (1975) in Russian; TR: Phys. Met. Metallogr., 40(4), 89 (1975). 81Min: L. Ming, M.H. Manghnani, and K.W. Katahara, J. Appl. Phys., 52, 1332 ( 1981). Published in Bull. Alloy Phase Diagrams, 3(1), June 1982. Complete evaluation contains 4 figures, 2 tables, and 35 references. 1