Фазовая диаграмма системы Al-Ti
К оглавлению: Другие диаграммы (Others phase diargams)
Al-Ti (Aluminum-Titanium)
J.L. Murray
The equilibrium solid phases of the Ti-Al system are (1) the bcc (bTi) and cph
(aTi) solid solutions; addition of Al stabilizes (aTi) relative to (bTi), and
the maximum solubilities of Al in (bTi) and (aTi) are about 48 and 45 at.%,
respectively; (2) Ti3Al, an ordered hexagonal structure based on (aTi) (Ti3Al
is also designated a2 in the literature); (3) TiAl, an ordered L10 fcc phase,
with a homogeneity range of approximately 48 to 68 at.% Al (TiAl forms from
the melt by a peritectic reaction with (bTi); (4) TiAl2 and d phases with
ordered fcc structures; the existence of these phases is established, but the
phase boundaries have not been determined, whereas two related structural
variants of TiAl2 have been reported, but details of the transition are not
yet known; (5) TiAl3, a stoichiometric phase with the D022 ordered fcc
structure and a low-temperature form, aTiAl3; and (6) the fcc (Al) solid
solution, in which the maximum Ti solubility is about 0.7 at.%.
The present assessment differs greatly from [Hansen], [Elliott], and [Shunk].
The (aTi)/Ti3Al boundaries are based on a critical reassessment of literature
through 1983 and on work performed in the present evaluator's laboratory [
84Shu]. The assessed diagram includes three additional phases--TiAl2, d, and
aTiAl3--discovered by [64Sch] and [65Ram].
At least three peritectic reactions occur in this system: two reactions, L + (
bTi) = TiAl [52Bum, 56Kor] and L + TiAl3 = (Al) [31Fin, 72Max, 74Cis, 74Ker,
78Shi], are well established. Near 75 at.% Al, peritectic microstructures have
also been observed-either the single-reaction L + TiAl = TiAl3, or two
reactions, L + TiAl = d and L + TiAl2 = TiAl3, which are plausible
interpretations of the data. The peritectic reaction L + TiAl3 = (Al) was
established by [31Fin]; the peritectic temperature is 665 с 0.5 C [31Fin, 72
Max, 74Cis, 74Ker, 78Shi].
The assessed (aTi)/Ti3Al boundaries are well established within about 1 at.%
in the range 0 to 25 at.% Al [67Bla, 70Bla]. Below about 850 C, the assessed (
aTi)/[(aTi) + Ti3Al] boundary represents the coherent, rather than the stable
incoherent, equilibrium. The (aTi)/Ti3Al boundary was also confirmed by [84Shu]
. Continuation of the order/disorder transition into the range 30 to 40 at.%
Al was confirmed by [79Muk], [77Bag], and [84Shu]. Because the ordered
transition cannot be suppressed during quenching, the microscopic evidence is
based on the nature of anti-phase boundaries.
[65Ram] observed a phase that existed only below 780 C, which they placed to
the Ti side of TiAl3. [73Loo] also found an allotropic change in TiAl3 at some
temperature below 638 C. The assessed diagram tentatively follows [73Loo],
but further experimental work is needed.
Rapid solidification produces (Al) solid solutions containing up to 0.2 at.%
Ti [34Boh, 52Fal]. Interest in solidification of dilute Al alloys is due to
the effectiveness of Ti as a grain refiner. [74Cis] and [74Ker] examined the
metastable extensions of the (Al) liquidus and solidus by measuring nucleation
temperatures as a function of cooling rate and by microprobe analysis of the (
Al) dendrites.
31Fin: W.L. Fink, K.R. Van Horn, and P.M. Budge, Trans. AIME, 93, 421-439 (
1931).
34Boh: H. Bohner, Z. Metallkd., 26(12), 268-271 (1934) in German.
52Bum: E.S. Bumps, H.D. Kessler, and M. Hansen, Trans. AIME, 194, 609-614 (
1952).
52Fal: G. Falkenhagen and W. Hofmann, Z. Metallkd., 43(3), 69-81 (1952) in
German.
56Kor: I.I. Kornilov, E.N. Pylaeva, and M.A. Volkova, Izv. Akad. Nauk SSSR,
Otd. Khim. Nauk, 7, 771-780 (1956) in Russian.
64Sch: K. Schubert, H.G. Meissner, A. Raman, and W. Rossteutscher,
Naturwissenschaften, 51(12), 287 (1964) in German.
65Ram: A. Raman and K. Schubert, Z. Metallkd., 56 44-52 (1965) in German.
67Bla: M.J. Blackburn, Trans. AIME, 239, 1200-1208 (1967).
70Bla: M.J. Blackburn, Sci. Technol. Appl. Titanium, Proc. Int. Conf., R.I.
Jaffee, Ed., 633-643 (1970).
72Max: I. Maxwell and A. Hellawell, Metall. Trans., 3(6), 1487-1493 (1972).
73Loo: F.J.J. van Loo and G.D. Rieck, Acta Metall., 21, 73-84 (1973).
74Cis: J. Cisse, H.W. Kerr, and G.F. Bolling, Metall. Trans., 5, 633-641 (1974)
.
74Ker: H.W. Kerr, J. Cisse, and G.F. Bolling, Acta Metall., 22(6), 677-686 (
1974).
77Bag: R.G. Baggerly, Advances in X-Ray Analysis, Vol. 18, Plenum Press, New
York, 1543-1552 (1977).
78Shi: K. Shibata, T. Sato, and G. Ohira, J. Cryst. Growth, 44, 435-445 (1978).
79Muk: P. Mukhopadhyay, Metallography, 12, 119-123 (1979).
84Shu: R.D. Shull, A.J. McAlister, and R. Reno, Proc. Fifth Int. Conf.
Titanium, G. Lutjering, U. Zwicker, and W. Bunk, Ed., Munich (1984).
Published in Phase Diagrams of Binary Titanium Alloys, 1987. Complete
evaluation contains 8 figures, 8 tables, and 103 references.
Special Points of the Ti-Al System