Фазовая диаграмма системы Mg-Tm

К оглавлению: Другие диаграммы (Others phase diargams)

Mg-Tm (Magnesium-Thulium) A.A. Nayeb-Hashemi and J.B. Clark The assessed Mg-Tm phase diagram in the Mg-rich region (0 to 12.58 at.% Tm) was determined by [77Rok1]. The rest of the diagram is based on the results of [64Kri], [64Mil], and [67Kri], and on extrapolation from the Mg-Gd system. The presence of three compounds (Mg24Tm5, Mg2Tm, and MgTm) has been well established. The existence of bcc (Tm) and a compound with MgyTmx stoichiometry (y/x >> 24/5) and their eutectoid decompositions, as reported by [64Mil] and [77Rok1], respectively, have not been confirmed. In the analysis of [Gschneidner], no arrest indicating an allotropic (cph to bcc) transition in pure Tm was shown. The microstructure of a 72 at.% Tm alloy reported by [ 64Mil] unequivocally shows the presence of a eutectoid reaction in the Tm-rich side of the diagram. Even without allotropy of pure Tm, the configuration shown in the assessed diagram allows for the presence of a "bcc (Tm)" phase and its eutectoid decomposition. Such a configuration may be found to prevail in the RE-rich region of the binary phase diagrams of Mg with Ho, Er, and Lu. However, this has been shown as a dashed line, because it has not been proven experimentally. MgyTmx (y/x >> 24/5) may exist. According to [77Rok1], this compound is unstable below 571 C. At this temperature, it decomposes by a eutectoid reaction to (Mg) and Mg24Tm5. The presence of such a compound was reported by [ 77Rok1] and [77Rok2] only for the Mg-Lu and Mg-Tm systems, and not for the Mg- Er, Mg-Ho, and Mg-Tb systems. Further investigation is needed to prove unequivocally the existence of this compound. In the assessed diagram, this compound is shown as a dashed line. [77Rok1] determined the solid solubility of Tm in (Mg) as 6.3 at.% Tm, which remained unchanged between the eutectoid temperature (571 C) and the eutectic temperature (592 C). The solid solubility of Mg in (Tm) has not been determined. However, from interpolation of the solid solubility of Mg in other heavy RE elements, a maximum solid solubility of ~87.5 at.% Tm (~12.5 at.% Mg) at 671 с 5 C may be expected. [73Bus] studied the magnetic properties of MgRE, CsCl-type compounds in the temperature range 4.2 to 300 K with magnetic fields up to 18 kOe. MgTm was not investigated. However, from interpolation of the results of [73Bus], MgTm would be expected to show Curie-Weiss behavior. [78Bus] studied the magnetic properties of Mg2RE compounds in the temperature range 1.5 to 300 K and the magnetic field of up to 18 kOe. According to [78Bus] , most of the Mg2RE compounds order ferromagnetically at temperatures "well below 100 K," except for Mg2La, Mg2Yb, and Mg2Y, which show Pauli paramagnetism; Mg2Sm and Mg2Eu order antiferromagnetically. The Curie temperature of Mg2Tm was found to be 19 K [78Bus]. 64Kri: P.I. Kripyakevich, V.I. Evdokimenko, and E.I. Gladysevskii, Kristallografiya, 9(3), 410-411 (1964) in Russian; TR: Sov. Phys. Crystallogr., 9(3), 330-331 (1964). 64Mil: A.E. Miller and A.H. Daane, Trans. AIME, 230, 568-572 (1964). 65Ian: A. Iandelli and A. Palenzona, J. Less-Common Met., 9, 1-6 (1965). 66Cha: C.C. Chao and P. Duwez, J. Appl. Phys., 37(7), 2631-2632 (1966). 67Kri: P.I. Kripyakevich and V.I. Evdokimenko, Z. Anorg. Allg. Chem., 355, 104- 112 (1967) in German. 73Bus: K.H.J. Buschow, J. Less-Common Met., 33, 239-244 (1973). 77Rok1: L.L. Rokhlin, Izv. Akad. Nauk SSSR, Met., (1), 181-183 (1977) in Russian; TR: Russ. Metall., (1), 152-154 (1977). 77Rok2: L.L. Rokhlin, Tsvetn. Metall., (5), 142-144 (1977) in Russian; TR: Sov. Non-Ferrous Met. Res., (5), 248-249 (1977). 78Bus: K.H.J. Buschow, R.C. Sherwood, and F.S.L. Hsu, J. Appl. Phys., 49(3), 1510-1512 (1978). Published in Phase Diagrams of Binary Magnesium Alloys, 1988. Complete evaluation contains 1 figure, 4 tables, and 20 references. Special Points of the Mg-Tm System