The Dy-Co system is investigated over the whole concentration range by means of Microscopy, Differential thermal analysis, X-ray Diffraction and Electron probe microanalysis. A phase diagram has been proposed. Six intermetallic compounds Dy_3Co, DyCo_2, Dy_2Co_7, DyCo_(5.2), DyCo_3 and Dy_2Co_(17) exist in this system, the latter two melt congruently and the others formed peritectically. The compound DyCo_(5.2) and Dy_2Co_(17) possess a homogeneity region at high temperature. The DyCo_(5.2) phase becomes unstable below 1100 ℃ (or a little higher temperature), and partialy decomposed, with Dy_2Co_(17) precipitating in the lead, into Dy_2Co_(17) and Dy_2Co_7. The structure of all these six compound have been determined. For compounds Dy_2Co_(17)a low- and a high-temperature modification is observed. Three eutectic reaction occur at 730 ℃ and 33.33 at.% Co, at 1325 ℃ and 80.50 at.% Co and at 1360 ℃ and 92.0 at.% Co respectively. There appears to be negligible solid solubility of Dy in Co.
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