Фазовая диаграмма системы Mn-Ti
К оглавлению: Другие диаграммы (Others phase diargams)
Mn-Ti (Manganese-Titanium)
J.L. Murray
The equilibrium solid phases of the Ti-Mn system are: (1) the bcc (bTi) and (
dMn) solid solutions, stable in pure Ti above 882 C and in pure Mn between
1246 and 1138 C; (2) the Ti-rich low-temperature cph (aTi) solid solution; (3)
the fcc (gMn) solid solution stable in pure Mn between 1100 and 1138 C; (4)
the complex cubic (bMn) solid solution, stable in pure Mn between 727 and 1100
C; (5) the complex cubic low-temperature (aMn) solid solution; (6) near-
equiatomic compounds aTiMn and bTiMn; (7) TiMn2, a Laves phase of the MgZn2
type with a broad homogeneity range, which melts congruently at 1325 C; (8)
the compound TiMn3, stable between about 950 and 1250 C; and (9) the compound
TiMn4 of composition 81.5 at.% Mn, stable between approximately 930 and 1230
C.
The crystal structures of TiMn3 and bTiMn, the positions of several phase
boundaries, and the temperatures of several three-phase equilibria have not
yet been determined experimentally or fully confirmed. The assessed phase
diagram is drawn from a calculation of the diagram from Gibbs energies
optimized with respect to select phase diagram data.
The (bTi) liquidus and solidus are based on thermal analysis, microstructural,
and incipient melting studies [53May]. An uncertainty of about с25 C is
estimated for these boundaries. The eutectic temperature is based on thermal
analysis studies of [57Hel] (1181 с 2 C) and [53May] (1175 C).
The assessed (bTi) transus lies between determinations of [51Mcq] and [53May]
and is based on optimization of Gibbs energies with respect to the data of [
53May]. The belief that the observed transus temperatures of [53May] are too
high is supported by the observation by [79Sal] that a 9 at.% Mn alloy was
single-phase (bTi) at 700 C. [53May] found the solubility of Mn in (aTi) to
be 0.4 с 0.1 at.% at the eutectoid temperature.
There has been controversy about the equiatomic compounds, because it was
originally assumed that only one phase existed between the (Ti) solutions and
TiMn2. There are two phases of near- equiatomic composition, aTiMn stable only
to about 950 C and bTiMn stable to at least 1150 C and therefore probably to
the melt [62Wat]. The L + TiMn2 = b TiMn peritectic reaction is placed at 1200
C based on thermal analysis on cooling [53May]. The (bTi) + bTiMn = aTiMn
peritectoid reaction occurs between 930 and 960 C [62Wat]. The compositions
of bTiMn and aTiMn are 52 and 50.5 at.% Mn, based on the X-ray and
microstructural work of [62Wat].
The TiMn2 liquidus was determined by [53May] and [57Hel] using thermal
analysis. The data of [57Hel] are preferred because of the care taken to avoid
contamination and attention to the possibility of composition changes during
melting.
The existence of one or more intermetallic compounds between TiMn2 and pure Mn
was deduced from thermal analysis data [57Hel]. X-ray and metallographic work [
61Wat] identified the two phases as TiMn3 and TiMn4 (about 81.5 at.% Mn), and
the reactions were interpreted as L + TiMn2 = TiMn3 and L + TiMn3 = TiMn4.
The (dMn) liquidus and solidus were investigated by [57Hel] and [58Mur]. Both
authors showed the formation of (dMn) by a eutectic reaction.
The effect of Ti additions on the allotropic transformation of Mn was
investigated by [57Hel] and [60Sav] using thermal analysis. There are
disagreements between the two investigations. The work of [57Hel] is preferred
because of the care to maintain and to document sample purity. The calculated
phase boundaries lie within about 5 C and 1 at.% of the input data and were
used to draw the assessed diagram. The (aMn) boundaries may require
significant modifications as further experimental data on the extent of the (
aMn) region become available.
In studies to measure the start temperature for the martensite (bTi) to (aTi)
transformation, (bTi) was found to be retained to room temperature when the Mn
content exceeds about 4 to 5 at.% [53Duw, 58Age]. w can form either during
quenching from the (bTi) region or during aging of metastable (bTi) alloys
below approximately 400 C [69Hic]. [58Age] reported as-quenched w phase
between 2.6 and 4.8 at.% Mn. When w phase forms during aging, the compositions
of w and (bTi) approach a metastable equilibrium at 5.1 and 19.1 at.% Mn [
69Hic].
51Mcq: A.D. McQuillan, J. Inst. Met., 80, 363-368 (1951).
53Duw: P. Duwez, Trans. ASM, 45, 934-940 (1953).
53May: D.J. Maykuth, H.R. Ogden, and R.I. Jaffe, Trans. AIME, 197, 225-231 (
1953).
57Hel: A. Hellawell and W. Hume-Rothery, Philos. Trans. R. Soc. (London), 249,
417-454 (1957).
58Age: N.V. Ageev and Z.M. Smirnova, Titanium and Its Alloys, Akad. Nauk SSSR,
1, 17-24 (1958).
58Mur: Y. Murakami and T. Enjyo, J. Jpn. Inst. Met., 22, 261-265 (1958) in
Japanese.
60Sav: E.M. Savitskii and Ch.V. Kopetskii, Zh. Neorg. Khim., 5, 2422-2434 (
1960); TR: Russ. J. Inorg. Chem., 5, 1173-1179 (1960).
61Wat: R.M. Waterstrat, Trans. AIME, 221, 687-690 (1961).
62Wat: R.M. Waterstrat, B.N. Das, and P.A. Beck, Trans. AIME, 224, 512-518 (
1962).
69Hic: B.S. Hickman, Trans. AIME, 245, 1329-1336 (1968).
79Sal: Y. Saleh and H. Margolin, Acta Metall., 27, 535-544 (1979).
Published in Phase Diagrams of Binary Titanium Alloys, 1987. Complete
evaluation contains 6 figures, 6 tables, and 36 references.
Special Points of the Ti-Mn System