Фазовая диаграмма системы Be-Hf

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Be-Hf (Beryllium-Hafnium) H. Okamoto and L.E. Tanner The basic features of the assessed (calculated) Be-Hf phase diagram are adopted primarily from [60Bed] and [80Tan], with review of the data of [61Kri2] , [79Kau], and [85Sau]. The phase boundaries in the assessed diagram are tentatively drawn according to the present thermodynamic model. The composition ranges of four intermediate phases, Be13Hf, Be17Hf2, Be5Hf, and Be2Hf, have not been determined. No experimental thermodynamic data are available for Be-Hf alloys. The models of [79Kau] and [85Sau] were modified to take into account the enthalpies of transformations for the pure elements, evaluated by [83Cha], and the assessed melting point of Be17Hf2. A preliminary calculation (assuming no solid solubility range for the constituent elements) indicated that the enthalpy of mixing for the liquid phase is almost symmetric. Therefore, a regular solution model has been employed for the liquid phase. The excess Gibbs energy was derived from the assessed eutectic point. Excess energies for solid solutions were adopted from [85Sau]. In the assessed diagram, the calculated diagram is drawn tentatively (in consideration of the scatter in available phase boundary data). The calculated homogeneity ranges of the Hf terminal solutions indicate expected magnitudes. They are influenced strongly by the Gibbs energies for the bcc and cph phases, which were somewhat arbitrarily chosen by [85Sau]. The liquidus boundaries were determined for the Be-rich regions by [61Kri2] and for the L = Be2Hg + (bHf) eutectic regions by [80Tan]. The temperature vs composition relationship reported by [61Kri2], however, is unusual and may not correspond to the true equilibrium condition. The eutectic point on the Be side could not be estimated from these data. The L = Be2Hf + (bHf) eutectic is located at 58 at.% Hf and 1125 C [80Tan]. The melting point of bBe and the bBe = aBe allotropic transformation temperature are 1289 с 5 and 1270 с 6 C, respectively [Melt]. Lattice parameter measurements did not reveal any solubility of Hf in (Be) [61Kri2]. The Be13Hf compound forms by a peritectic reaction at 1620 с 50 C [60Bed]. The stability of this phase at low temperatures is uncertain. [61Boo] suggested that this phase is unstable at 1400 с 100 C, but [60Bed] showed Be13Hf as stable down to room temperature. The present thermodynamic model is based on [60Bed] and [61Boo] for the high- and low-temperature limits of stability, respectively. It has not been determined whether Be17Hf2 consists of two forms, aBe17Hf2 (Be-poor side) and bBe17Hf2 (Be-rich side), or one form. [61Boo] obtained a compound by hotpressing, tentatively identified as Be21Hf2, which is likely to be identical with bBe17Hf2 [Elliott]. The melting point of bHf and the bHf = aHf allotropic transformation temperature are 2231 and 1743 C, respectively [Melt]. Calculated solubility limits of Be in (Hf) in the assessed diagram should be considered schematic. A fully glassy structure forms by a rapid liquid-quenching (>105 C/s) in the composition range of 40 to 70 at.% Hf [80Tan]. A CrB-type metastable phase, BeHf, was also found by [80Tan]. The solubility limit of Be in (bHf) was found to extend to about 7.5 at.% by liquid-quenching. Acicular martensite (a›) forms from primary (bHf) during cooling, in the composition range from 95 to 100 at.% Hf [80Tan]. 60Bed: R.G. Bedford, U.S. At. Energy Comm. UCRL-5991-T, 7 p (1960). 60Pai: R.M. Paine and J.A. Carrabine, Acta Crystallogr., 13(8), 680-681 (1960). 60Zal: Z. Zalkin and D.E. Sands, U.S. At. Energy Comm. UCRL-5988-T, 6 p (1960). 61Boo: J. Booker, R.M. Paine, and A.J. Stonehouse, Tech. Rept. WADD-TR-60-889 ( AD 265625), 142 p (1961). 61Kri1: P.I. Kripyakevich, M.A. Tylkina, and E.M. Savitskii, Kristallografiya, 6(1), 117-118 (1961) in Russian; TR: Sov. Phys. Crystallogr., 6(1), 94 (1961). 61Kri2: P.I. Kripyakevich, M.A. Tylkina, and E.M. Savitskii, Zh. Struct. Khim., 2(4), 424-433 (1961) in Russian; TR: J. Struct. Chem. USSR, 2, 395-403 (1961). 61Rud: E. Rudy, F. Benesovsky, H. Nowotny, and L.E. Toth, Monatsh. Chem., 92, 692-700 (1961). 61Zal: A. Zalkin, D.E. Sands, R.G. Bedford, and O.H. Krikorian, Acta Crystallogr., 14(1), 63-65 (1961). 79Kau: L. Kaufman and L.E. Tanner, Calphad, 3(2), 91-107 (1979). 80Tan: L.E. Tanner, Acta Metall., 28(12), 1805-1816 (1980). 83Cha: M.W. Chase, Bull. Alloy Phase Diagrams, 4(1), 123-124 (1983). 85Sau: N. Saunders, Calphad, 9(4), 297-309 (1985). Published in Phase Diagrams of Binary Beryllium Alloys, 1987. Complete evaluation contains 2 figures, 4 tables, and 15 references. 1