Фазовая диаграмма системы Os-Ti

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Os-Ti (Osmium-Titanium) J.L. Murray The assessed Ti-Os phase diagram is based on the results of a single experimental study [71Ere, 72Ere, 75Sht] that clearly established the topology of the diagram. However, [71Ere] noted that equilibrium was difficult to achieve over the composition ranges 20 to 45 and 67 to 95 at.% Os. This fact, coupled with some internal inconsistencies in the data and the implausibility of several phase boundaries, suggests that further experimental work is needed. In particular, the (aTi)/(bTi) boundaries and the (Os) liquidus, solidus, and solvus require further examination. A eutectic reaction L = TiOs + (Os) was observed at 2100 C, and the eutectic composition was estimated from microstructural data as 65 at.% Os. [71Ere] reported the maximum solubility of Ti in (Os) to be approximately 21 at.% (79 at.% Os), based on microstructural data. This conflicts with solidus data near the eutectic temperature. The liquidus and solidus in the assessed diagram are shown as straight lines between the melting point of Os and the appropriate compositions at the eutectic isotherm. Based on microstructural observations of annealed samples, the solubility of Ti in (Os) decreases to between 5 and 10 at.% Ti at 1000 C. [71Ere] showed that the solubility decreased significantly between the eutectic temperature and 1800 C, then remained essentially constant and large down to 1000 C. The assessed solvus is redrawn from the phase diagram of [71Ere] with a smoother curvature, but it is not inconsistent with the microstructural data. [71Ere] also determined the (aTi)/(bTi) boundaries using differential thermal analysis and metallographic examination of alloys annealed at 600 and 800 C. The observation of a single-phase (aTi) structure alloy at 1 at.% Os and 800 C (a very large solubility at that temperature) suggests that difficulties, either in equilibrating alloys or in identifying the phases, may have caused errors in both the (aTi) solvus and the (bTi) transus. [71Ere] found that metastable (bTi) can be retained during quenching in alloys of Os content greater than approximately 3 at.%. For lower Os content, (bTi) transforms martensitically to the cph (a›Ti) form during quenching. 71Ere: V.N. Eremenko, R.D. Shtepa, and E.L. Semenova, Izv. Akad. Nauk SSSR, Met.,(4), 210-213 (1971) in Russian; TR: Russ. Metall., (4), 147-149 (1971). 72Ere: V.N. Eremenko and R.D. Shtepa, Colloq. Int. CNRS, (205), 403-413 (1972). 75Sht: T.D. Shtepa, Fiz. Khim. Kondens. Faz. Sverkhtverd. Mater., 175-191 ( 1975) in Russian. Published in Phase Diagrams of Binary Titanium Alloys, 1987, and Bull. Alloy Phase Diagrams, 3(2), Sep 1982. Complete evaluation contains 3 figures, 4 tables, and 7 references. Special Points of the Ti-Os System