Фазовая диаграмма системы Ca-Yb

К оглавлению: Другие диаграммы (Others phase diargams)

Ca-Yb (Calcium-Ytterbium) K.A. Gschneidner, Jr. and F.W. Calderwood The assessed Yb-Ca phase diagram is based on the work of [68Sod], who used differential thermal analysis and electrical resistivity measurements to locate the solidus-liquidus lines and the fields of fcc and bcc solid solubility. Samples were prepared from Yb and Ca metals that were initially in the form of distilled crystals. Seven Yb-Ca alloys were prepared by encapsulating weighed charges of the distilled crystals in Ta crucibles and heating to 900 C with a 60-h hold under a vacuum of 10 -5 torr. Metallographic examination of alloys containing 19.5, 39.9, and 60.1 at.% Ca, vacuum annealed 2 h at 250 C, showed single-phase structure and supported the assumption that a continuous solid solution exists at room temperature. Pure Ca occurs in two stable forms. The low-temperature form, aCa, has the fcc Cu-type structure and is stable below 443 C. Above this temperature, bCa has the W-type bcc structure. In the assessed phase diagram, the melting points and transition temperatures have been adjusted to agree with the accepted values. The melting temperature reported for Yb (814 C), was 5 C below the accepted value (819 C), and the temperature of the b = a transformation, 796 C, was 1 C above the accepted temperature for this parameter. The values for the melting temperature of Ca ( 842 C) and for the b = a transformation in Ca (443 C) are the accepted values for these parameters. Each of the seven alloy specimens prepared by [68Sod] showed two two-phase regions, one between the liquidus and the solidus and the other between the bcc and fcc single-phase solid fields. The evidence strongly suggests two continuous solid-solution regions, a bcc field at high temperatures below the solidus and the fcc field at lower temperatures. A minimum in the melting temperature occurs at 25.0 с 5 at.% Ca and 810 с 2 C. [68Sod] observed a marked similarity between this phase diagram and those of the Ca-Ba and Ca-Sr systems, in that each has a minimum in the melting point and each has a narrow temperature range between the liquid and solid fields. 68Sod: S.D. Soderquist and F.X. Kayser, J. Less-Common Met., 16, 361 (1968). Published in Bull. Alloy Phase Diagrams, 8(6), Dec 1987. Complete evaluation contains 1 figure, 1 table, and 2 references. 1