Фазовая диаграмма системы Mo-Ti

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Mo-Ti (Molybdenum-Titanium) J.L. Murray The equilibrium solid phases of the Ti-Mo system are (1) the bcc (bTi,Mo) solid solution, in which Ti and Mo are completely miscible above the transformation temperature of pure Ti (882 C); and (2) the cph (aTi) solid solution with restricted solubility of Mo. There have been two conflicting descriptions of the phase stability of (bTi,Mo) . [51Duw], [51Han], [70Ron], and [72Ron] reported that the temperature of the ( bTi) transus decreases monotonically with Mo content and discovered no evidence for a miscibility gap in (bTi,Mo). The work of [77Ter] and [78Ter] established the miscibility gap and monotectoid reaction in the equilibrium diagram. The results of metallography, transmission electron microscopy, electrical resistivity, and lattice parameter measurements were in agreement not only about the existence of the two bcc phases, but also about the positions of the phase boundaries. [77Ter] reported the monotectoid reaction at 675 C based on electrical resistivity data. Recent differential thermal analysis [84Mca] indicates that the reaction occurs at a somewhat higher temperature, about 695 C. Because of the greater purity of the samples [84Mca], this value is accepted for the equilibrium diagram. The monotectoid composition is placed at 12 at.% Mo. The miscibility gap has been calculated by optimization of the bcc excess Gibbs energy with respect to miscibility gap data on the Ti-rich side, and the calculated miscibility gap was used to draw the assessed phase diagram. The solidus was investigated by [51Han] and [69Rud]. [69Rud] used the Pirani technique to determine incipient melting temperatures and estimated the liquidus to lie slightly above the temperature at which samples collapsed. [ 51Han] determined temperatures of incipient melting by metallographic examination of quenched specimens, with an uncertainty of с25 C. The solidus data of [51Han] and [69Rud] are accurately fitted by thermochemical calculations. Because the temperature of sample collapse cannot be used as a quantitative measure of the liquidus, the present calculation is used to predict the liquidus. The maximum solubility of Mo in (aTi) is approximately 0.4 at.% Mo at [51Han]. Start temperatures for the martensitic b to a transformation have been reported. In alloys containing more than 5 to 6 at.% Mo, the bcc phase (or ( bTi) + w) is retained completely during quenching; that is, the martensitic start temperature falls below room temperature [51Duw]. Martensitic (a›Ti) forms between 0 and 2 at.% Mo. In alloys containing 2 to 4 at.% Mo, the (a››Ti) martensite has an orthorhombic structure. The w phase can form either during quenching from the (bTi) region (athermally) , or after low-temperature aging of quenched alloys. As-quenched w phase formation starts at approximately 4 at.% Mo, but there is no good agreement about the maximum Mo content at which w is formed. The aged form of w occurs in alloys of composition between approximately 4 and 15 at.% Mo [75Bag]. The optimal aging temperature is approximately 350 C. 51Duw: P. Duwez, Trans. AIME, 191, 765-771 (1951). 51Han: M. Hansen, E.L. Kamen, and H.D. Kessler, Trans. AIME, 191, 881-888 ( 1951). 69Rud: E. Rudy, Technical Rept. AFML-TR-65-2, Part V, Wright Patterson Air Force Base (1969). 70Ron: G.N. Ronami, S.M. Kuznetsova, S.G. Fedotov, and K.M. Konstantinov, Vestn. Moskovskogo Univ., Fiz., 25(2), 186-189 (1970) in Russian; TR: J. Moscow Univ.; Phys., 25(2), 55-57 (1970). 72Ron: G.N. Ronami, Kristall und Technik, 7(6), 615-638 (1972) in German. 75Bag: R.G. Baggerly, Metallography, 8, 361-373 (1975). 77Ter: S. Terauchi, H. Matsumoto, T. Sugimoto, and K. Kamei, J. Jpn. Inst. Met. , 41(6), 632-637 (1977) in Japanese. 78Ter: S. Terauchi, H. Matsumoto, T. Sugimoto, and K. Kamei, Tech. Rept. Kansai Univ., 19, 61-71 (1978). 84Mca: A.J. McAlister, private communication (1984). Published in Phase Diagrams of Binary Titanium Alloys, 1987. Complete evaluation contains 5 figures, 5 tables, and 45 references. Special Points of the Ti-Mo System