Фазовая диаграмма системы P-Ti

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P-Ti (Phosphorus-Titanium) J.L. Murray The equilibrium solid phases of the Ti-P system are (1) the solid solutions, cph (aTi) and bcc (bTi); (2) TiP and TiP2 with the TiAs and Al2Cu structures ( the former is a superstructure of NiAs); and (3) a number of subphosphides- Ti3P, Ti2P, Ti4P3, Ti1.7P, and Ti5P3. In the assessed diagram, the phases Ti1. 7P and Ti5P3 are included. The maximum solubility of P in (bTi) is 0.3 at.% P. The solubility of P in (aTi) has not been determined, but based on the (bTi) solvus, it must be very low. Phases based on pure P are not considered in the present assessment. The assessed Ti-P phase diagram is based primarily on work of [65Ere] and [68Sne]. There is some disagreement in the range between Ti2P and Ti4P3, which tentatively is attributed to solid-state transformations occurring during quenching. The diagram is thus uncertain and incomplete. Other work on the system has been primarily on preparation and crystal structure analysis of the compounds. [65Ere] provided a phase diagram covering the range 0 to 50 at.% P. Thermal analysis data were plotted for the three-phase equilibria, and uncertainties were assigned to the invariant temperatures. Information on experimental techniques, heat treatments, purity of the alloys, or microstructures were not given, however. It is therefore not possible to assess the accuracy of the two- phase boundaries or to resolve discrepancies, except hypothetically. [68Sne] used visual determinations of melting points (с50 C), X-ray diffraction of single-crystal and powder samples, and metallography. [68Sne] verified most of the diagram of [65Ere], but did not report sufficient details of their experiments to permit a quantitative data assessment. Concerning the phase equilibria involving Ti3P, [65Ere] and [68Sne] are in agreement. [65Ere] placed a reaction L = (bTi) + Ti3P at 1495 с 5 C with a eutectic composition 9.5 at.% P. At 1450 and 1300 C, the solubility of P in ( bTi) was given as 0.2 [65Ere] and 0.08 at.% [68Sne]. [68Sne] verified the eutectic temperature and composition by optical pyrometry and metallographic examination of as-cast alloys. Ti2P was prepared by [65Ere] and [68Sne]. According to [65Ere], Ti3P and Ti2P melt peritectically at 1760 с 10 C and 1920 с 10 C, respectively. [68Sne] verified these reactions and noted that a metastable eutectic between Ti2P and (bTi) was observed in arc-melted alloys. Beyond Ti2P, the phase diagram becomes complicated. [65Ere] showed a tetragonal phase, Ti3P2, that melts congruently at 2098 C, has a broad homogeneity range near the melting point, and is stoichiometric below 1800 C. A stoichiometric cubic phase, Ti4P3, melts by a peritectic reaction at 2060 с 15 C [65Ere, 68Sne]. [65Ere] did not observe Ti5P3 or Ti1.7P. Ti5P3 was stable up to at least 1500 C [68Sne]. [68Sne] verified the stability and symmetry of Ti4P3 and also confirmed that Ti4P3 forms by a peritectic reaction. They observed that powder patterns of as-cast alloys in the range 35 to 45 at.% P are very complex. Ti5P3 has some homogeneity range, but the lattice parameter variation with composition is not reproducible. Because of its structure, Ti5P3 is contaminated easily, and contamination may also influence its range of stability. The present hypothesis is that Ti5P3 is stable to the liquidus and has a homogeneity range of several percent at high temperatures. Ti1.7P and possibly other structures could be formed during quenching of high-temperature single-phase Ti5P3. TiP was assigned the homogeneity range 47.9 to 48.5 at.% P ([38Bil], X-ray diffraction) and 48.6 to 49.4 at.% P ([66Gin], Knudsen cell technique). The latter work established only the Ti-rich boundary and cited unpublished work that placed the P-rich side nearer 50 at.% P. TiP2 has been examined by [68Sne] and others. In this composition range, inclusion of the gaseous phase and an account of the effect of pressure are needed to describe the phase diagram. Accordingly, the phase diagram is drawn only in the range 0 to 55 at.% P. 38Bil: W. Biltz, A. Rink, and F. Wiechmann, Z. Anorg. Chem., 238, 395-405 ( 1938) in German. 65Ere: V.M. Eremenko and V.E. Listovnichii, Dop. Akad. Nauk Ukr. SSR, (9), 1176-1179 (1965) in Russian. 66Gin: K.A. Gingerich, Adv. Mass. Spectrom., Proc. Conf. 3, 1009-1016 (1966). 68Sne: P. Snell, Acta Chem. Scand., 22, 1942-1952 (1968). Published in Phase Diagrams of Binary Titanium Alloys, 1987. Complete evaluation contains 1 figure, 2 tables, and 14 references. Special Points of the Ti-P System