Фазовая диаграмма системы Fe-Ni

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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. 20Han: D. Hanson and H.E. Hanson, J. Iron Steel Inst., 102, 39-64 (1920). 23Han: D. Hanson and J.R. Freeman, J. Iron Steel Inst., 107, 301-321 (1923). 23Mck: L.W. McKeehan, Phys. Rev., 21, 402-407 (1923). 25Kas: T. Kase, Sci. Rept., Tohoku Imp. Univ., 14, 173-217 (1925). 26Osa: A. Osawa, Science Rept., Tohoku Imp. Univ., 15, 387-398 (1926). 30Rob: O.L. Roberts and W.P. Davey, Metals and Alloys, 1, 648-654 (1930). 31Ben: H. Bennedek and P. Schafmeister, Arch. 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Phys., 53, 7939- 7941 (1982). 82Rhy: J.J. Rhyne, Bull. Alloy Phase Diagrams, 3, 402 (1982). Published in Phase Diagrams of Binary Nickel Alloys, 1991. Complete evaluation contains 18 figures, 8 tables, and 250 references. 1