Фазовая диаграмма системы Nb-Ti

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Nb-Ti (Niobium-Titanium) J.L. Murray The assessed Ti-Nb phase diagram does not differ qualitatively from previous evaluations [Hansen, Elliott, Shunk]. The stable equilibrium diagram is without invariant reactions, congruent transformations, or critical points. [51Han] examined heat treated alloys microscopically for signs of incipient melting; an uncertainty of с25 C was assigned to the data based on the temperature interval examined. [69Rud] and [69Zak] made optical observations of incipient melting: an uncertainty of с20 C is estimated for Ti-rich alloys and somewhat more for the Nb-rich alloys. Experimental data are not available for the liquidus because of the narrow melting range. The liquidus was estimated by thermodynamic calculations, with an uncertainty of probably no more than с2 at.%. [64Bro] determined the (bTi,Nb) transus by resistivity measurements on cooling and verified the results by rapid quenching experiments [66Bro]. The results of [64Bro] and [66Bro] showed the transus to be lower in temperature than previous determinations by as much as 150 C at 25 at.% Nb. Rapid quenching methods have been shown to be necessary to determine the (bTi,Nb) transus. The effect of sample contamination is also to raise the apparent temperature of the transus. The present assessment is therefore based primarily on the work of [64Bro] and [66Bro]. The assessed phase boundary is placed somewhat above the resistivity ( cooling) results. The recent determination of the volume fractions of (aTi) and (bTi,Nb) in equilibrium at 400 C [82Gus] supports placing the equilibrium (bTi,Nb) transus somewhat above the resistivity results. (bTi,Nb) can transform martensitically during quenching to the cph (a›Ti) form for low Nb content or to an orthorhombic distortion of the cph form (a›Ti) for higher Nb content. The metastable w phase can form either during quenching from the (bTi,Nb) field or during aging at temperatures below about 450 C. As-quenched w is found in the approximate composition range 13 to 18 at.% Nb [58Bag, 69Hic]. [ 69Hic] found w in the range 9 to 30 at.% Nb after aging at 450 C. [80Osa] proposed a wider range on the Nb-side; w was found in a 36 at.% Nb alloy, but the precipitation was very slow. During aging, the (bTi,Nb) matrix is depleted in Nb, and a metastable two-phase equilibrium between w and (bTi,Nb) is approached. Based on lattice parameter data, [69Hic] found compositions of 9 to 30 at.% Nb for w and (bTi,Nb), respectively, at 450 C. [73Afo] studied w phase formation in 10 and 20 at.% Nb alloys under pressure; w phase was formed at 30 and 50 kbar, respectively. Using a shock wave of amplitude 320 с 20 kbar, [79Sik] also produced w in 10 and 20 at.% Nb alloys previously annealed in the two-phase (bTi,Nb) + (aTi) region. 51Han: M. Hansen, E.L. Kamen, H.D. Kessler, and D.J. McPherson, Trans. AIME, 191, 881-888 (1951). 58Bag: Yu.A. Bagariatskii, G.I. Nosova, and T.V. Tagunova, Dokl. Akad. Nauk SSSR, 122, 593-596 (1958) in Russian; TR: Sov. Phys. Dokl., 3, 1014-1018 (1958) . 64Bro: A.R.G. Brown, D. Clark, J. Eastabrook, and J.S. Jepson, Nature, 201, 914-915 (1964). 66Bro: A.R.G. Brown and K.S. Jepson, Mem. Sci. Rev. Metall., 63(6), 575-584 ( 1966) in French. 69Hic: B.S. Hickman, Trans. Metall. Soc. AIME, 245, 1329-1335 (1969). 69Rud: E. Rudy, Tech. Rep. AFML-TR-65-2, Part V, Wright Patterson Air Force Base (1969). 69Zak: A.M. Zakharov, V.P. Pshokin, and A.I. Baikov, Izv. V.U.Z. Tsvetn. Metall., (6), 104-108 (1969) in Russian. 73Afo: N.S. Afonikova, V.F. Degtyareva, Yu.A. Litvin, A.G. Rabin'kin, and Yu.A. Skakov, Fiz. Tverd. Tela, 15, 1096-1101 (1972) in Russian; TR: Sov. Phys. Solid State, 15(4), 746-749 (1973). 79Sik: V.N. Sikorov and V.F. Degtyareva, Fiz. Metal. Metalloved., 48(1), 211- 213 (1979) in Russian; TR: Phys. Met. Metallogr., 48(1), 181-182 (1979). 80Osa: K. Osamura, E. Matsubara, T. Miyatani, Y. Murakami, T. Horiuchi, and Y. Monju, Titanium '80, Sci. Tech., Proc. 4th Int. Conf. Titanium, Kyoto, Japan, 1369-1377 (1980). 82Gus: L.N. Guseva and L.K. Dolinskaya, Dokl. Akad. Nauk SSSR, 266(3), 634-637 (1982) in Russian; TR: Dokl. Chem., 334-337 (1982). Published in Phase Diagrams of Binary Titanium Alloys, 1987. Complete evaluation contains 6 figures, 3 tables, and 44 references. 1