Фазовая диаграмма системы Fe-Ni
К оглавлению: Другие диаграммы (Others phase diargams)
Fe-Ni (Iron-Nickel)
L.J. Swartzendruber, V.P. Itkin, and C.B. Alcock
The equilibrium phases of the Fe-Ni system are (1) the liquid, L; (2) the (dFe)
solid solution based on the high-temperature bcc Fe; (3) the (gFe,Ni) solid
solution based on the fcc Fe and Ni; (4) the (aFe) solid solution based on the
low-temperature bcc Fe; and (5) the FeNi3 intermetallic compound, which forms
by a first-order order-disorder transformation below 517 C and has an
extended range of solid solubility.
The assessed diagram has been obtained by thermodynamic modeling of the
experimental data [23Han, 25Kas, 31Ben, 36Jet, 37Jen, 49Jon, 49Owe, 50Jos,
53Rhi, 57Hel, 63Heu, 65Gol, 80Rom, 81Dee]. The liquidus and solidus for Fe-
rich alloys up to about 12 at.% Ni were measured by [57Hel]. According to [
23Han], the minimum in the liquidus curve is located at 1438 C (temperatures
quoted throughout have been converted to IPTS-68) and about 67 at.% Ni.
According to [37Jen], the minimum is between 1422 and 1427 C. Based on a
least-squares fit, taking into account both the measured boundaries and
available thermodynamic data, the most probable location for the minimum was
calculated to be 1440 C and 66.0 at.% Ni, in good agreement with [23Han]. The
liquidus and solidus separations in the assessed diagram are based primarily
on those predicted by the measured thermodynamic parameters in the liquid and
fcc phases, with the assessed boundary location giving greatest weight to the
measurements of the liquidus.
Comparisons with thermodynamic measurements and with liquidus and solidus
measurements indicate a narrow two-phase a + d region and a narrow peritectic
reaction L + a <259> g at 1514 с 2 C and 3.5, 4.9, and 4.2 (с0.5) at.% Ni,
respectively.
Due to the sluggishness of the g <259> a and a <259> g phase transformations
below 800 C, the a/g equilibrium boundaries are difficult to determine. The
boundaries shown in the assessed diagram were constructed using the data of [
49Owe], [49Jon], [65Gol], and [80Rom], giving greatest weight to the results
of [80Rom].
In annealed thin films, [63Heu] concluded that the (gFe,Ni) phase decomposes
eutectoidally to (aFe) and FeNi3 at 345 C and 52 at.% Ni. The critical
behavior of the temperature derivative of the resistivity around the FeNi3
composition was investigated by [82Ore]. No anomaly in the resistivity was
found at the order-disorder temperature, but one was found at the Curie
temperature.
[81Dee] explained a 15 C hysteresis zone between order and disorder as a
magnetic effect. [72Cal] found that the order-disorder transformation of FeNi3
was not second order and observed a two-phase zone of 5 or 6 C for alloys
between 71 and 75 at.% Ni. [54Iid] concluded that short-range order forms in
FeNi3 before long-range order is observable by other methods.
By extrapolating the magnetization vs temperature curves, [53Wak] estimated
the Curie temperatures for ordered FeNi3 and found a higher Curie temperature
for the ordered alloys than for the disordered alloys. The Curie temperature
of pure Ni is taken as 627.4 K in accordance with [82Rhy].
Alloys of high maximum permeability, the permalloys, can be formed by rapidly
cooling alloys near the FeNi3 composition [64Sch]. [75Ind] has shown how the
Curie temperature variation in (gFe,Ni) may be closely fitted to a Redlich-
Kister form with a single interaction term. [77Mio] has shown how this
interaction parameter is related to the two-moment model for gFe of [63Wei].
At low temperature (less than about 800 C), the a + g field in Fe-Ni is
relatively broad and the attainment of equilibrium involves considerable
diffusion. Diffusion rates at these lower temperatures are low, and very long
times are required to establish equilibrium. Normal conditions favor a
diffusionless (or martensitic) transformation, which exhibits considerable
hysteresis. [20Han] determined two sets of boundaries for the a + g two-phase
region-one on heating and one on cooling. This g/(a + g) boundary agrees
closely with that determined by thermal analysis (the a/(a + g) boundary is
not detected by thermal analysis). [20Han] also concluded that the a + g
transformation is accelerated by the presence of impurities.
Considerable supercooling of liquid Fe-Ni alloys is possible. [78Con] observed
supercooling of up to 150 K in an alumina crucible for alloys between 6 and 90
at.% Ni.
Alloys containing approximately 20 to 50 at.% Ni (invar alloys) exhibit
anomalous thermomechanical and thermochemical behavior, including a region of
very low coefficient of thermal expansion. [79Cha] has shown that these invar
anomalies tend to disappear in alloys that have been electron irradiated to
enhance diffusion and thereby accelerate the approach to true equilibrium. It
is probable that the invar anomalies are a characteristic of metastable alloys.
An orthorhombic phase in thin films with a composition in the a + g region of
the equilibrium diagram was indicated by [58Pin]. This phase was not retained
above 650 C. [56Cec] postulated that small particles of 30 at.% Ni that were
rapidly cooled from the liquid state could pass directly to the a phase.
The existence of ordered structures based on Fe3Ni and FeNi has been proposed
by several investigators. For the equiatomic composition, an order-disorder
reaction below 321 с 2 C has been reported by [62Pau] for alloys that have
been heavily irradiated by neutrons. An FeNi superstructure was observed in
meteorites by [77Pet]. In a study of meteorites, [82Jag] found that
compositions of 30 to 40% Ni consisted of ordered g + ordered FeNi, whereas [
79Lin] found decomposition into a + g with ~5 and 48 wt.% Ni, respectively.
The FeNi and Fe3Ni ordered structures are not shown on the assessed diagram.
It is probable that these ordered phases are metastable or unstable structures
reached in alloys in which the sluggish g = a + FeNi3 eutectoid reaction has
been suppressed. [61Kau] showed that pressure lowers the g <259> a
transformation temperature.
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Published in Phase Diagrams of Binary Nickel Alloys, 1991. Complete evaluation
contains 18 figures, 8 tables, and 250 references.
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