Фазовая диаграмма системы Cu-Ti

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Cu-Ti (Copper-Titanium) J.L. Murray The equilibrium solid phases of the Ti-Cu system are (1) the solid solutions based on the pure components: cph (aTi), the stable form of Ti below 882 C; bcc (bTi), the stable form of Ti between 882 C and the melt; and fcc (Cu); (2) the essentially stoichiometric compound Ti2Cu with the MoSi2 structure; (3) TiCu (B11 structure), which has a homogeneity range of 48 to 52 at.% Cu and melts congruently at 985 C; (4) the essentially stoichiometric compounds Ti3Cu4, Ti2Cu3, and TiCu2 with related crystal structures; and (5) high- and low-temperature polymorphs bTiCu4 and aTiCu4, each with the approximate homogeneity range 78 to 80.9 at.% Cu. The maximum solubilities of Cu in (aTi) and (bTi) are 1.6 and 13.5 at.% at 790 and 1005 C, respectively. The maximum solubility of Ti in (Cu) is 8 at.% at 885 C. Metastable ordered structures can form in this composition range before the appearance of equilibrium bTiCu4. The calculated phase boundaries incorporated in the assessed diagram by [83Mur] have been retained in the present version. Experimental phase diagram data for Ti-Cu are uneven in accuracy. The structures and compositions of the compounds have been carefully determined and verified, but many of the phase boundaries involving liquid and solid solutions were examined only by [52Jou]. Metastable equilibria have been thoroughly investigated; studies cover the decomposition of supersaturated cph and fcc solutions and the formation of noncrystalline alloys from 30 to 75 at.% Cu. Between the congruent melting point of TiCu and the eutectic reaction at 73 at. % Cu, there is a cascade of peritectic reactions involving the compounds Ti3Cu4, Ti2Cu3, TiCu2, and TiCu4. A number of different phase diagrams have been proposed [53Trz, 66Ere, 66Zwi]. [65Sch] and [66Ere] made mutually consistent structural identifications of the phases Ti3Cu4, Ti2Cu3, and TiCu2. By etching studies and microprobe analysis of as-cast samples, [63Pie] estimated the peritectic compositions. [53Trz] and [66Ere] agreed that two solid-state reactions occur within about 20 C of the eutectic temperature. Based on the reaction types, the liquidus compositions, and compositions of the intermetallic compounds, the phase diagram must have the topology given by [65Sch] and [66Ere]. There are two equilibrium TiCu4 phases. bTiCu4 is an established stable phase; aTiCu4 was once thought to be a metastable coherent phase, which after long aging even at low temperature is succeeded by bTiCu4. Recent transmission electron microscopy work showed that bTiCu4 transforms during cooling to aTiCu4 and, therefore, aTi Cu4 is the stable low- temperature phase [83Bru]. Cu-rich alloys age harden. The accepted description of the kinetics of decomposition of supersaturated (Cu) is as follows. During quenching, a solid solution containing more than about 4 at.% Ti begins to undergo spinodal decomposition into Ti-enriched and Ti-depleted disordered phases. In the early stages of aging, sidebands in diffraction data indicate a periodic lattice strain due to oriented coherent particles. After a critical composition of the Ti-rich clusters is reached, ordering begins. (bTi) transforms martensitically to the cph structure during quenching. The addition of Cu to (bTi) does not cause the bcc structure to be retained after quenching at any composition. [68Ray] reported a noncrystalline phase in splat-quenched alloys from 65 to 70 at.% Cu. It was later observed that glasses could be formed over the range 30 to 75 at.% Cu using the chill-block melt-spinning technique [ 82Woy]. Metastable crystalline phases are also observed in rapidly solidified alloys. [71Gie] found a metastable phase TiCu3(m), which is distinct from the equilibrium compounds. The solid solubility of Ti in (Cu) can be extended to about 20 at.% Ti [71Gie]. 52Jou: A. Joukainen, N.J. Grant, and C.F. Floe, Trans. AIME, 194, 766-770 ( 1952). 53Trz: W. Trzebiatowski, J. Berak, and T. Romotowski, Roczn. Chem., 27, 426- 437 (1953) in Polish. 63Pie: P. Pietrokowsky and J.R. Maticich, X-Ray and X-Ray Microanalysis, 3rd Int. Symp., 591-602 (1963). 65Sch: K. Schubert, Z. Metallkd., 56(3), 197-198 (1965) in German. 66Ere: V.N. Eremenko, Y.I. Buyanov, and S.B. Prima, Poroshk. Metall. Akad. Nauk Ukr. SSR, 6(6), 77-87 (1966) in Russian; TR: Soviet Powder Met., (6), 494- 502 (1966). 66Zwi: U. Zwicker, E. Kalsch, T. Nishimura, D. Ott, and H. Seilstorfer, Metall, 20(12), 1252-1255 (1966) in German. 68Ray: R. Ray, B.C. Geissen, and N.J. Grant, Scr. Metall., 2, 357-359 (1968). 71Gie: B.C. Giessen and D. Szymanski, J. Appl. Crystallogr., 4, 257-259 (1971). 82Woy: C. Woychik and T.B. Massalski, private communication (1982). 83Bru: J.Y. Brun, J. Sylvaine, T. Hamar, and H.A. Colette, Z. Metallkd., 74(8), 525-529 (1983). 83Mur: J. Murray, Bull. Alloy Phase Diagrams, 4(1), 81-95 (1983). Published in Phase Diagrams of Binary Titanium Alloys, 1987. Complete evaluation contains 8 figures, 11 tables, and 85 references. Special Points of the Ti-Cu System