Фазовая диаграмма системы Fe-W

К оглавлению: Другие диаграммы (Others phase diargams)

Fe-W (Iron-Tungsten) S.V. Nagender Naidu, A.M. Sriramamurthy, and P. Rama Rao The equilibrium phases of the Fe-W system are (1) the Fe-rich bcc solid solution, (aFe); (2) the Fe-rich fcc solid solution, (gFe); (3) the W-rich bcc solid solution, (W); and (4) two intermediate phases, Fe7W6 (m) and FeW (d). The system is characterized by two peritectic reactions and one peritectoid reaction producing the (aFe), m, and d phases, respectively, and one eutectoid decomposition, the m phase giving rise to the (aFe) and d phases. The assessed phase diagram is based primarily on the work of [48Syk], [67Sin], [73Kir], [ 81Hen], and [83Ray]. A characteristic feature of the phase diagram is the occurrence of a g loop. There is a minimum in the Fe-rich liquidus, with (aFe) solidifying congruently. The maximum solubility of W in (aFe) is 14.3 at.% at the peritectic temperature of 1548 C [67Sin]; in (gFe), it is 1.46 at.%. The maximum solubility of Fe in (W) is 2.6 at.% [48Syk]. The intermediate phases m and d occur over limited ranges of homogeneity. The solubility of W in (aFe) decreases from 14.3 at.% at 1548 C to 4.6 at.% at 1190 C. At lower temperatures, there is considerable scatter in the reported values. As the lower solubility limits reported by [67Sin] correspond to longer annealing times, they are considered to represent equilibrium values. The dashed solvus line below 1000 C corresponds to the extrapolation of the solvus through the data of [67Sin]. The Curie temperature of pure Fe is 770 C [82Swa]. The Curie temperature of ( aFe) is not markedly affected by W content. Pure Fe undergoes a transition from the low-temperature bcc aFe to the fcc gFe at 912 C, which reverts to the bcc dFe at 1394 C [82Swa]. The addition of W was found to raise the lower transition temperature and lower the upper transition temperature, thus closing the g phase field. The contours of the g loop are based on the data of [73Kir]. [81Hen] reported that with long time annealing treatments (>2000 h), Fe2W (l phase) is a metastable transitional phase arising from the decomposition of the m phase at about 1000 C; l persists because of its structural similarities with m. In conventional heat treatments involving holding at about 1000 C; and below, it is unlikely that durations of 1000 h will be used. In such situations, therefore, d (FeW) might not form; instead, l (Fe2W) along with m (Fe7W6) will persist, as reflected in the Fe-W phase diagram in [ 67Sin]. 48Syk: W.P. Sykes, Metals Handbook, American Society for Metals, 1220 (1948). 67Sin: A.K. Sinha and W. Hume-Rothery, J. Iron Steel Inst., 205, 1145-1149 ( 1967). 73Kir: G. Kirchner, H. Harvig, and B. Uhrenius, Metall. Trans., 4, 1059-1067 ( 1973). 81Hen: E.T. Henig, H. Hofmann, and G. Petzow, Plansee Seminar 1981, H.M. Ortner, Ed., Reutte, Austria, Metallwerk Plansee, 335-359 (1981). 82Swa: L.J. Swartzendruber, Bull. Alloy Phase Diagrams, 3(2), 161-165 (1982). 83Ray: G.V. Raynor and V.G. Rivlin, Int. Met. Rev., 28, 122-129 (1983). Published in J. Alloy Phase Diagrams, 2(3), Sep 1986. Complete evaluation contains 5 figures, 7 tables, and 80 references. Special Points of the Fe-W System