Фазовая диаграмма системы Al-Ti

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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