Фазовая диаграмма системы C-Co

К оглавлению: Другие диаграммы (Others phase diargams)

C-Co (Carbon-Cobalt) K. Ishida and T. Nishizawa The assessed phase diagram for the Co-C system is based primarily on the data of [85Has]. According to [87Gui], the (aCo) solid solution decomposes into (eCo) and graphite at 421.5 C by a eutectoid reaction. The solubility of C in the (eCo) phase at the eutectoid temperature is estimated to be 8.74 x 10-4 at.% C. Two kinds of metastable carbides, Co2C and Co3C, were formed by carburizing thin films of Co prepared by evaporation [61Nag]. Co2C and Co3C were formed at temperatures in the range 450 to 500 C. Both carbides decomposed gradually to (eCo) containing stacking faults and graphite. The decompositions began at 450 and 477 C and finished at 469 and 491 C for Co2C and Co3C, respectively. Co2C was also obtained by spraying carbon onto a preheated cobalt film [81Lny], and Co3C was formed in high-carbon alloys (>22 at.% C) by quenching from the liquid state at 1950 to 2500 C [65Ver]. In splat-quenching experiments on an 11.2 at.% C alloy, a supersaturated (aCo) phase with a lattice constant of 0. 3586 nm and Co3C were obtained [67Ruh]. A metastable diagram with diamond and Co3C was computed by [82Ers], which showed that the phase equilibria of Co-diamond and Co-Co3C are of the same eutectic type as the stable Co-graphite diagram. The temperature of the diamond eutectic is ~90 C less than the temperature of the graphite eutectic. The carbide equilibria are even less stable than those with diamond. However, Co3C becomes stable above a pressure of about 45 kbar. The metastable equilibria between liquid, graphite, and (eCo) were calculated by [87Gui], who estimated the metastable eutectic temperature to be 1257 C. At lower temperatures, a (aCo) = (eCo) martensitic transformation occurs. The Ms temperature is lowered by the addition of C, whereas the reverse As temperature increases. [82Ers] calculated the stable and metastable phase equilibria at constant pressures of 1 atm, 60 kbar, and 100 kbar. Under high pressure, the equilibrium of diamond with Co3C is stabilized, whereas no equilibrium occurs between diamond and (aCo). The Curie temperatures of the (aCo) solid solution were measured by [37Kos] and [38Has]. Thermodynamic analysis of the solid solubility of C in (aCo) by [ 85Has] and [87Gui] clarified that, in lowering the Curie temperature by the addition of C, the calculated slope is considerably less negative than the experimental values. Further studies of the effect of C on Curie temperature are required. 37Kos: W. K”ster and E. Schmid, Z. Metallkd., 29, 232-233 (1937) in German. 38Has: U. Haschimoto and N. Kawai, J. Jpn. Inst. Met., 2, 26-28 (1938) in Japanese. 61Nag: S. Nagakura, J. Phys. Soc. Jpn., 16, 1213-1219 (1961). 65Ver: A.A. Vertman, V.K. Grigorovich, N.A. Nedumov, and A.M. Samarin, Dokl. Akad. Nauk SSSR, 162, 1304-1305 (1965) in Russian; TR: Dokl. Chem., 162, 593- 595 (1965). 67Ruh: R.C. Ruhl and M. Cohen, Scr. Metall., 1, 73-74 (1967). 72Cad: M.C. Cadeville and M.F. Lapierre, Scr. Metall., 6, 399-404 (1972) in French. 81Lny: V.N. Lnyanoy and S.A. Chepur, Izv. Akad. Nauk SSSR, Metall., (5), 161- 162 (1981) in Russian; TR: Russ. Metall., (5), 123-124 (1981). 82Ers: T.P. Ershova, D.S. Kamenetskaya, and L.P. Ilina, Izv. Akad. Nauk SSSR, Met., (1), 153-160 (1982) in Russian; TR: Russ. Metall., (1), 130-137 (1982). 83Nis: T. Nishizawa and K. Ishida, Bull. Alloy Phase Diagrams, 4(4), 387-390 ( 1983). 85Has: M. Hasebe, H. Ohtani, and T. Nishizawa, Metall. Trans., 16A, 913-921 ( 1985). 87Gui: A.F. Guillermet, Z. Metallkd., 78, 700-709 (1987). 87Nik: B.I. Nikolin, N.N. Shevchenko, T.L. Sizova, and A.Yu. Babkevich, Scr. Metall., 21, 1169-1174 (1987). Submitted to the APD Program. Complete evaluation contains 3 figures, 7 tables, and 39 references. 1