Фазовая диаграмма системы Co-W

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Co-W (Cobalt-Tungsten) S.V. Nagender Naidu, A.M. Sriramamurthy, and P. Rama Rao The assessed Co-W phase diagram consists of: (1) the liquidus, passing through a maximum at 1505 C and 10 at.% W; (2) a eutectic at 1471 C and 21 at.% W; ( 3) a peritectic horizontal at 1689 C, with terminal compositions of 32 and 99. 1 at.% W; (4) Co7W6, formed peritectically at 48.5 at.% W, with rhombohedral crystal structure; (5) the fcc solid solution, (aCo), with a maximum solid solubility of 17.5 at.% W; (6) Co3W, formed as a result of a peritectoid reaction at 1093 C and 25.3 at.% W, with hexagonal crystal structure; and (7) the solid solution, (W), with a maximum solid solubility of 0.9 at.% Co at 1689 C. The assessed phase diagram is basically the same as that of [Hansen]. The calculated phase diagram of [78Kau] closely resembles the experimental phase diagram. The Co-rich liquidus rises with addition of W from 1495 C, the melting point of Co, to a maximum temperature of about 1505 C around 10 at.% W, then falls to the eutectic at 1471 C and 21 at.% W. Subsequently, the liquidus rises to a peritectic horizontal at 1689 C with the liquid composition of 32 at.% W [67Neu, 84Gab]. According to [81Tak], the solubility limit of W in (aCo) falls from 17.5 at.% at 1471 C to as low as 0.5 at.% at as high a temperature as 750 C. The solubilities of W in (aCo) and (eCo) are not likely to vary greatly, especially at lower temperatures. [67Neu] established the solubility of Co in ( W) to be about 0.9 at.% at the peritectic temperature and 0.7 at.% at 700 C. There is considerable hysteresis in the aCo = eCo transformation. The transformation temperature during heating was found to increase with additions of W, and it was found to decrease during cooling. The three-phase transformation involving (aCo), (eCo), and Co3W is likely to occur at a temperature close to the a <259> e transformation temperature for pure Co, 422 C. The Curie temperature was found to decrease from 1121 C for pure Co to 750 C for a solid solution of about 6 at.% W in (aCo) [32Kos, 36Tak, 37Has]. The descending Curie temperature curve meets the solvus at 865 C and about 4 at.% W. 32Kos: W. Koster and W. Tonn, Z. Metallkd., 24, 296-299 (1932) in German. 36Tak: S. Takeda, Sci. Rep. Res. Inst. Tohoku Univ., Honda Anniv. Vol., 864- 881 (1936). 37Has: U. Haschimoto, J. Jpn. Inst. Met., 1, 177-190 (1937) in Japanese. 67Neu: L.A. Neumeier and J.L. Holman, U.S. Bur. Mines Rep. Invest. 6956 (1967). 78Kau: L. Kaufman and H. Nesor, Calphad, 2(1), 81-108 (1978). 81Tak: T. Takayama, M.Y. Wey, and T. Nishizawa, Trans. Jpn. Inst. Met., 22, 315-325 (1981). 84Gab: A. Gabriel, thesis, Univ. Grenoble, France (1984). Published in J. Alloy Phase Diagrams, 2(1), Jan 1986. Complete evaluation contains 3 figures, 7 tables, and 33 references. Special Points of the Co-W System