Фазовая диаграмма системы Cu-Ti
К оглавлению: Другие диаграммы (Others phase diargams)
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