Фазовая диаграмма системы Be-Cr

К оглавлению: Другие диаграммы (Others phase diargams)

Be-Cr (Beryllium-Chromium) M. Venkatraman and J.P. Neumann The Cr-Be system is characterized by two intermetallic phases, CrBe2 and CrBe12, which are assumed to be in equilibrium with each other. Although no investigations have been carried out in the region between CrBe2 and CrBe12, the existence of intermetallic phases in this region cannot be ruled out. The assessed phase diagram is based on the work of [55Edw] and [81Pug]. The Cr-Be system is similar to the Fe-Be system and exhibits the isotypic phases CrBe2 (FeBe2, MgZn2 type), and CrBe12 (FeBe12, Mn12Th type). CrBe2 has a very narrow homogeneity range. According to [55Edw], the homogeneity range of CrBe2 on the Be-rich side may be approximately 0.5 at.%. However, an additional phase (FeBe5) is known to occur in the Fe-Be system, so that the existence of the analogous CrBe5 phase appears likely. Limited information is available on the phase diagram from ~98 to 100 at.% Be. Experimental work in this region is extremely difficult, because of the small solubility of Cr in solid (Be) and the strong influence of impurities on the melting point and the solid-state phase transformation of Be. Temperatures in the present evaluation have been adjusted to IPTS-68. An invariant three-phase equilibrium exists at 1238 C, which must be a catatectic reaction: (bBe) (~0.2 at.% Cr) = L (~2 at.% Cr) + (aBe) (~0.1 at.% Cr). The solubility of Cr in (Be) above the eutectic temperature is approximately 0.2 at.% Cr [60Gel]. The solubility of Cr in (aBe) below the eutectic temperature is approximately 0.08 at.% Cr. The high-temperature bcc (bBe) phase is suspected of being more ductile than the low-temperature cph (aBe) phase. Therefore, the influences of alloying elements on the a = b transformation temperature has been studied to obtain a broad, stabilized (bBe) phase field. In this respect, the Cr-Be system shows little promise because of the limited solubility of Cr in (Be). Addition of Be decreases the N‚el temperature of pure Cr from 311.5 to ~16 0 K at 1.3 at.% Be . CrBe12 has a ferromagnetic Curie temperature of 50 K. 55Edw: A.R. Edwards and S.T.M. Johnstone, J. Inst. Met., 84, 313-317 (1955-56). 60Gel: S.H. Gelles and J.J. Pickett, Tech. Rep. U.S. At. Energy Comm., NMI- 1218 44 p (1960). 81Pug: M.S. Pugachov, L.F. Verkhorobin, M.M. Matyushenko, G.P. Tikhinskii, and Yu.G. Titov, Dop. Akad. Nauk Ukr. RSR, (2), 88-91 (1981) in Russian. Published in Phase Diagrams of Binary Beryllium Alloys, 1987, and Bull. Alloy Phase Diagrams, 7(1), Feb 1986. Complete evaluation contains 4 figures, 1 table, and 19 references. 1