Фазовая диаграмма системы Co-Cr

К оглавлению: Другие диаграммы (Others phase diargams)

Co-Cr (Cobalt-Chromium) K. Ishida and T. Nishizawa The equilibrium phases of the Co-Cr system are (1) the liquid, L; (2) the fcc solid solution, (aCo); (3) the cph solid solution, (eCo); (4) the bcc solid solution, (aCr); and (5) the intermetallic compound, s phase. The assessed phase diagram is based on the experimental data and thermodynamic calculations of [78All] and [82Has]. The phase diagram is somewhat different from that of [ Hansen], especially in the solid phase equilibria above 1200 C. The intermediate phase d proposed by [49Els] was not found by the high-temperature X-ray diffraction examination of [78All]. The liquidus and solidus lines for the Cr-rich side of the diagram have not been established due to the difficulty of preparation of high-purity specimens and the high-temperature measurements. Determination of phase equilibria between (aCo) and (eCo) in the Co-rich portion below 800 C is difficult because of sluggish diffusion in attaining equilibrium. This portion of the assessed phase diagram is based on the thermodynamic calculations of [82Has], which suggests that the two-phase separation to the ferromagnetic and paramagnetic phases occurs in both the ( aCo) and (eCo) phases due to the magnetic effect. These phase equilibria at low temperatures are important not only from the thermodynamic viewpoint, but also in the practical sense, because the perpendicular magnetic recording system developed by [78Iwa] uses Co-Cr thin films to memorize a large quantity of information. It is highly possible that the Co-rich columnar crystals of cph with [0001] axis surrounded by a Cr-rich paramagnetic matrix are the units of fine memory [86Mae]. The great possibility of the origin of the modulated structure is due to the magnetic-induced miscibility gap in the (eCo) phase [86Mae]. The allotropic transformation of pure Cr from bcc to a high-temperature structure has been suggested many times, but the evidence is so questionable that the aCr phase is probably stable at all temperatures below the melting point [Pearson2]. Pure Cr of the special structure dCr is produced by evaporation and condensation in a pure argon atmosphere at low pressures, whereas the ordinary bcc structure is formed when the argon contains a small amount of air or oxygen [67Kim]. The (dCr) phase was confirmed to exist in the composition range greater than 57 at.% Cr. A metastable Ni3Sn-type ordered structure of Co3Cr was reported by [69Sin], but the evidence to support this phase is not strong because it was ascertained by the presence of only one weak superlattice line (101). [76Gud] investigated the crystal structure in splat-cooled Co - (10 to ~65. 8) at.% Cr alloys from the liquid state. The (aCo) phase is stabilized up to 65.8 at.% Cr and the (aCr) phase crystallizes instead of formation of s phase. Pure Cr is antiferromagnetic and the N‚el temperature is 38.5 C [85And]. Antiferromagnetic ordering in the s phase was estimated from the magnetic specific heat at low temperatures by [83Mar]. The N‚el temperature is close to that of pure Cr. 49Els: A.R. Elsa, A.B. Westerman and G.K. Manning, Trans. AIME, 185, 579-602 ( 1949). 67Kim: K. Kimoto and I. Nishida, J. Phys. Soc. Jpn., 22, 744-756 (1967). 69Sin: A.K. Sinha, Trans. Metall. Soc. AIME, 245, 237-240 (1969). 72Yuk: N. Yukawa, M. Hida, T. Imura, M. Kawamura, and Y. Mizuno, Metall. Trans. , 3, 887-895 (1972). 76Gud: V.N. Gudzenko and A.F. Polesya, Fiz. Met. Metalloved., 41, 1106-1109 ( 1976) in Russian; TR: Phys. Met. Metallogr., 41, 189-193 (1976). 78All: C. Allibert, C. Bernard, N. Valignat, and M. Dombre, J. Less-Common Met. , 59, 211-228 (1978). 78Iwa: S. Iwasaki and K. Ouchi, IEEE Trans. Magn. Magn., 17, 849-851 (1978). 82Has: M. Hasebe, K. Oikawa, and T. Nishizawa, J. Jpn. Inst. Met., 46, 577-583 (1982) in Japanese. 83Mar: J.F. Martin and D.B. Downie, J. Chem. Thermodyn., 15, 691-699 (1983). 83Nis: T. Nishizawa and K. Ishida, Bull. Alloy Phase Diagrams, 4(4), 387-390 ( 1983). 83Wal: R. Walmsley, J. Thompson, D. Friedman, R.M. White, and T.H. Geballe, IEEE Trans. Magn. Magn., 19, 1992-1994 (1983). 85And: J. Anderson, Int. J. Thermophys., 6, 411-423 (1985). 86Mae: Y. Maeda, M. Asahi, and M. Seki, Jpn. J. Appl. Phys., 25, L668-670 ( 1986). Published in Bull. Alloy Phase Diagrams, 11(4), Aug 1990. Complete evaluation contains 7 figures, 13 tables, and 54 references. Special Points of the Co-Cr System