Фазовая диаграмма системы Hf-V

К оглавлению: Другие диаграммы (Others phase diargams)

Hf-V (Hafnium-Vanadium) J.F. Smith The assessed diagram for the Hf-V system is based on [68Rud] and [69Rud]. The diagram is closely related to the V-Zr diagram, except that the single intermediate phase melts congruently rather than peritectically. Generally, the existence of one intermediate phase in the system, at a stoichiometry of HfV2 with a C15 MgCu2-type structure is accepted. Studies with higher-purity materials confirmed the existence and structure of this phase an agreed that it is without polymorphic transition above room temperature [61Ell, 77Min]. The assessed diagram shows (bHf) dissolving 23.5 at.% V at 1456 C in eutectic equilibrium with liquid at 43 at.% Hf and HfV2 near 65 at.% V. (bHf) disproportionates at 1190 C in eutectoidal equilibrium with (aHf) containing < 2 at.% V and HfV2 having composition also near 65 at.% V. On the V-rich side, HfV2 has a maximum V content near 67 at.% V at 1520 ш C, where it is in eutectic equilibrium with liquid at 69 at.% V and the terminal solution with about 96 at.% V. HfV2 is indicated to melt congruently near 66 at.% V. The HfV2 phase, like the V2Zr phase, has received considerable attention because of the martensitic transformation in the region 100 to 120 K and the superconducting transition near 8.4 to 9.6 K. The martensitic transition is first order because there is both a volume discontinuity [76Iva] and a latent heat effect [79Rap]. [82Bal2] showed that for V2Zr a number of structures are competitive below the martensitic transition. Presumably, this also applies to HfV2. There is some evidence that the martensitic transition actually is two transitions [78Pan, 80Fin, 82Bal, 83Bal]. An initial second-order electronic transition is followed at slightly lower temperature by a first-order crystallographic transition. A variety of factors, including heat treatment, stoichiometry, and chemical purity, affect the transition [78Pan]. Grain size has a pronounced effect [79Koz, 81Gal]. In the Hf-V system, the superconducting transition temperature was reported to reach a maximum at 80 at.% V [78Fin]. Because this was not a single-phase alloy, the maximum was rationalized as a pressure effect from excess V acting on the HfV2, but this was not proven. In contrast, the maximum transition temperature in the V-Zr system was found at the ideal stoichiometry of V2Zr [ 78Fin]. Measurements at high pressures [84Ber] show that the superconducting transition temperature of HfV2 first increases with increasing pressure to reach a maximum near 25 kbar and then drops monotonically to the highest pressure of measurement at 220 kbar. The same report indicates that the martensitic transition first becomes smeared at about 10 kbar and is not detectable at 28 kbar and above. Rapid quenching of Hf-rich alloys can produce multi-phase materials [80Ten]. However, at compositions near that of the Hf-rich eutectic, amorphous materials with no detectable crystallinity can be obtained [80Ten, 82Gil]. 61Ell: R.P. Elliot, Trans. ASM, 53, 321-329 (1961). 68Rud: E. Rudy and St. Windisch, J. Less-Common Met., 15, 13-27 (1968). 69Rud: E. Rudy, Compendium of Phase Diagram Data, U.S. Govt. Rep AFML-TR-65-2, Part V, Air Force Materials Laboratory, Wright-Patterson AFB, 14-15 and 94 ( 1969). 76Iva: V.E. Ivanov, V.A. Finkel', and E.A. Pushkarev, Dokl. Akad. Nauk SSSR, Riz. Khim., 228, 119-122 (1976) in Russian; TR: Dokl. Phys. Chem., 228, 415- 417 (1976). 77Min: S. A. Minaeva and P.B. Budberg, Izv. Akad. Nauk SSSR, Met., (1) 206- 210 (1977) in Russian; TR: Russ. Metall., (1) 177-181 (1977). 78Fin: T.R. Finlayson and H.R. Khan, Appl. Phys., 17, 165-172 (1978). 78Pan: V.M. Pan, I.E. Bulakh, A.L. Kasatkin, and A. Shevchenko, J. Less-Common Met., 62, 157-166 (1978). 79Koz: V.N. Kozhanov, Ye. R. Romanov, S.V. Verkhovskii, and A.P. Stepanov, Fiz. Met. Metalloved., 48, 1249-1255 (1979) in Russian; TR: Phys. Met. Metallogr., 48(6), 108-114 (1979). 80Fin: V.A. Finkl' and E.A. Pushkarev, Zh. Eksp. Teor. Fiz., 78, 842-846 (1980) in Russian; TR: Sov. Phys. JETP, 51, 422-424 (1980). 80Ten: M. Tenhover, Appl. Phys., 21, 279-282 (1980). 81Gal: E.V. Galoshina, V.N. Kozhanov, S.V. Verkhovskii, M.A. Borozdina, Ye.P. Romanov, T.S. Shubina, and K.N. Mikhalev, Fiz. Met. Metalloved., 52, 1205-1214 (1981) in Russian; TR: Phys. Met. Metallogr., 52(6), 68-76 (1981). 82Bal: A.S. Balankin, Fiz. Tverd. Tela (Leningrad), 24, 3475-3477 (1982) in Russian; TR: Sov. Phys. Solid State, 24, 1977-1978 (1982). 82Gil: L. Gillott, P.N. Guile, N. Cowlam, and K.H.J. Buschow, Struct. Non- Cryst. Mater., 10, 455-464 (1982). 83Bal: A.S. Balankin and D.M. Skorov, Izv. Akad. Nauk SSSR, Neorg, Mater., 19, 161-162 (1983) in Russian; TR: Inorg. Mater., 19, 142-144 (1983). 84Ber: I.V. Berman, N.B. Brandt, B.N. Kodess, I.E. Kostyleva, and V.I. Sidorov, Fiz. Tverd. Tela, 26, 1812-1818 (1984) in Russian; TR: Sov. Phys. Solid State, 26, 1095-1098 (1984). Published in Phase Diagrams of Binary Vanadium Alloys, 1989. Complete evaluation contains 1 figure, 2 tables, and 33 references. Special Points of the Hf-V System