Фазовая диаграмма системы Rh-Ti

К оглавлению: Другие диаграммы (Others phase diargams)

Rh-Ti (Rhodium-Titanium) J.L. Murray There are qualitative disagreements about the Ti-rich part of the Ti-Rh phase diagram, and two versions of the phase equilibria are given in the assessed diagram. On the Ti-rich side, the solid curves are based on the work of [66Rau] , and the dotted curves are based on the work of [72Ere] and [75Sht]. All investigators agree on the existence of Ti2Rh, bTiRh, and TiRh3. The features about which there is fair agreement are the (aTi)/(bTi) boundaries, the homogeneity range of TiRh3, part of the (Rh) solvus, and the congruent melting point of bTiRh. The most serious discrepancies concern the extent of the single-phase (bTi) field. [72Ere] claimed that the maximum solubility of Rh in (bTi) is at least 37.5 at. % Rh. They did not observe CsCl superlattice lines in X-ray diffraction patterns in alloys containing less than 37.5 at.% Rh. The X-ray results were supported by metallographic evidence that the same alloys were single phase after annealing at 1000 C. [66Rau], however, presented metallographic evidence that a 30 at.% Rh alloy was two phase at 1270 C; their as-cast microstructures supported a eutectic reaction at about 30 at.% Rh. Because both [72Ere] and [66Rau] presented positive evidence in favor of their versions of the diagram, the discrepancy cannot be resolved by reinterpretation of the data. Both versions are therefore shown. The solubility of Rh in (aTi) is <0.07 at.% [66Rau]. [72Ere] found the (bTi) transus to lie at approximately 6 to 7 at.% Rh at 600 C, using metallographic techniques. In metallographic and X-ray studies, [66Rau] reported that the ( bTi) transus lies between 8 and 12 at.% Rh at 700 C. Three structures have been observed between 35 and 60 at.% Rh [66Rau]. The NbRu-type phase is not included in the assessed diagram as an equilibrium phase. [66Rau] and [72Ere] agree that the microstructures of alloys containing more than 45 at.% Rh showed signs of transformation during quenching. The assessed diagram is based on the interpretation given by [72Ere]. The high-temperature form of the equiatomic compound has the CsCl structure, and only at less than 45 at.% Rh can the CsCl structure be retained during quenching. On the Rh-rich end of the single-phase aTiRh field, there are discrepancies between the two studies, because [72Ere] did not take the phase Ti3Rh5 into account. The work of [66Rau] is therefore used to place this boundary at 58 с 2 at.% Rh between 1500 and 1760 C. [69Gie] made structural determinations of Ti3Rh5 and Hf3Rh5 by X-ray powder diffraction. Ti3Rh5 has a unique orthorhombic structure isomorphous with Ge3Rh5 and related to Ni3Ti. Ti3Rh5 is included as a line compound in the assessed phase diagram. [66Rau] reported that TiRh3 melts congruently at about 1760 C and has a eutectic reaction with (Rh) at 1720 с 50 C. [72Ere] claimed that it is formed by a peritectic reaction at 1750 с 50 C. An as-cast microstructure of an 81 at.% Rh alloy does not allow for a eutectic reaction [72Ere]. The peritectic reaction is therefore shown. [66Rau] also identified a compound with a cubic structure in alloys containing 81 to 90 at.% Rh that had been annealed below 1100 C. The existence of such a phase was not verified by [72Ere], and further attempts to identify its structure have not been made. 66Rau: E. Raub and E. Roschel, Z. Metallkd., 57, 546-551 (1966) in German. 69Gie: B.C. Giessen, R. Wang, and N.J. Grant, Trans. Metall. Soc. AIME, 245, 1207-1210 (1969). 72Ere: V.N. Eremenko and R.D. Shtepa, Colloq. Int. CNRS, (205), 403-413 (1972) in German. 75Sht: T.D. Shtepa, Fiz. Khim. Kondens. Faz. Sverkhtverd. Mater., 175-191 ( 1975) in Russian. Published in Phase Diagrams of Binary Titanium Alloys, 1987. Complete evaluation contains 3 figures, 6 tables, and 16 references. Special Points of the Ti-Rh System