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