Фазовая диаграмма системы Ti-U

К оглавлению: Другие диаграммы (Others phase diargams)

Ti-U (Titanium-Uranium) J.L. Murray The Ti-U phase diagram has been investigated by [53Buz], [54Udy], [55Kna], and [61Add]. The diagram proposed by [53Buz] differs from other proposed diagrams in the number of equilibrium phases and invariant reactions. The disagreements can be attributed in part to the contamination of the alloys used by [53Buz] during heat treatments and in part to misinterpretation of microstructures that arise from nonequilibrium transformations during quenching. Among [54Udy], [55Kna], and [61Add], there are some quantitative but no qualitative disagreements. The most pronounced discrepancies involve the homogeneity ranges of the phases and the position of the eutectoid point on the Ti-rich side of the diagram. In the present diagram, liquidus data were derived from thermal analysis [ 53Buz] or visual observation of melting [54Udy, 55Kna]. Solidus data were derived from metallographic examination of heat treated and quenched specimens. The high liquidus temperatures [53Buz] are due to contamination of alloys by beryllia crucibles. [54Udy] noted similar high melting points in their preliminary work. The liquidus and solidus data of [55Kna] were used for the optimization of Gibbs energies. [54Udy] is in substantial agreement with [ 55Kna]. Experimental data on solid phase equilibria were obtained by [53Buz], [54Udy], [55Kna], [58Mur], and [61Add]. [61Add] used microprobe analysis of equilibrated diffusion couples. Other work was done by metallography and X-ray diffraction, supplemented by dilatometry [55Kna]. The studies of [53Buz] and [ 58Mur] were restricted to U-rich alloys, and [58Mur] studied primarily mechanical properties. The assessed diagram is based on [55Kna] and [61Add]. The major discrepancies involve the number of equilibrium intermetallic phases [53Buz], the homogeneity range of TiU2 [54Udy], the composition and temperature of the eutectoid points [54Udy, 55Kna, 61Add], and the solubility of Ti in (aU), (bU), and (gU) [58Mur, 54Udy, 55Kna]. The solubility of U in (aTi) was measured by microprobe analysis of annealed diffusion couples [61Add] and by autoradiography [55Kna]. Results were 0.9 at.% U and 0.7 to 0.8 at.% U, respectively, and the present calculations yield 1.0 at.% U, in good agreement with these results. There is considerable scatter in the data on the (bTi)/[(bTi) + (aTi)] boundary. The eutectoid reaction is sluggish, and based on the low value of the reported eutectoid temperature and the relatively few alloys examined in this region, the data of [54Udy] can be rejected in favor of [55Kna] and [ 61Add]. The remaining discrepancy between [55Kna] and [61Add] is tentatively resolved by the thermodynamic calculation. Particular attention has been given to phases formed metastably from (gU) and ( bU). [56Har] reported that, with pure enough alloys and high enough cooling rates, alloys containing more than 7 at.% Ti can be retained in the bcc structure. In the range 2 to 5.5 at.% Ti, an orthorhombic martensite with an acicular microstructure (a a ›) appears; in the range 5.5 to 10.5 at.% Ti, a banded microstructure appears [53Buz, 54Udy, 55Kna]. a› and aa › are the result of the transformation (bU) <259> (aU), but the a b › martensite is formed directly from the bcc phase [66Ana]. At 11 at.% Ti, the martensite becomes distorted to a monoclinic structure designated a b›, and in the range 11.4 to 17 at.% Ti, a b › coexists with g0, a tetragonal phase. Single-phase g0 can be obtained in alloys containing more than 17 at.% Ti [66Ana]. In quenched bcc alloys of composition near TiU2 stoichiometry, equilibrium TiU2 forms coherent precipitates in the bcc matrix [70Tom]. Coherent TiU2 is also referred to as "diffuse TiU2" [55Kna]. 53Buz: R.W. Buzzard, R.B. Liss, and D.P. Fickle, J. Research Nat. Bur. Stand., 50(4), 209-214 (1953). 54Udy: M.C. Udy and F.W. Boulger, Trans. AIME, 200, 207-210 (1954). 55Kna: A.G. Knapton, J. Inst. Met., 83, 497-504 (1954-55). 56Har: A.G. Harding, J. Inst. Met., 84, 532-535 (1956). 58Mur: D.J. Murphy, Trans. ASM, 50, 884-904 (1958). 61Add: Y. Adda, M. Beyeler, A. Kirianenko, and F. Maurice, Mem. Sci. Rev. Met., 58(9), 716-724 (1961) in German. 66Ana: M. Anagnostidis, R. Baschwitz, and M. Colombie, Mem. Sci. Rev. Met., 63( 2), 163-168 (1966) in German. 70Tom: R.D. Tomlinson, J.M. Silcock, and J. Burke, J. Inst. Met., 98, 154-160 ( 1970). Published in Phase Diagrams of Binary Titanium Alloys, 1987. Complete evaluation contains 5 figures, 4 tables, and 15 references. Special Points of the Ti-U System