Фазовая диаграмма системы Pt-Ti

К оглавлению: Другие диаграммы (Others phase diargams)

Pt-Ti (Platinum-Titanium) J.L. Murray [57Nis] performed the only comprehensive phase diagram study of the Ti-Pt system. Additional work has been done on the structure and composition ranges of the intermetallic compounds, and four compounds were not accounted for by [ 57Nis]. Thus, significant modifications of the diagram of [57Nis] are required, but the additional information provided by subsequent studies is not sufficient to determine a complete new phase diagram. [70Don] studied the B2 to B19 structural transformation using high-temperature X-ray diffraction. The equilibrium phase relations were not determined; they also measured the start and finish temperatures for the transformations on heating and cooling. The phase relations involving Ti3Pt5 and TiPt3- have not been investigated in detail. [69Sin] found three phases in a 73 at.% Pt alloy annealed at 900 C: TiPt3-, g, and aTiPt. The presence of aTiPt rather than Ti3Pt5 suggests the possibility of a eutectoid reaction Ti3Pt5 = aTiPt + TiPt3- above 900 C. According to [57Nis], eutectic was present in as-cast alloys containing less than 66 at.% Pt, but a 73 at.% Pt alloy showed evidence of a peritectic reaction. Therefore, the Pt-rich compounds are sketched in the following manner. The eutectic reaction at 1780 C with eutectic composition 58 at.% Pt is identified as the reaction L = aTiPt + Ti3Pt5 rather than L = aTiPt + g. A congruent melt is shown for Ti3Pt5 and another eutectic reaction L = Ti3Pt5 + TiPt3-. The temperatures of the hypothetical reactions are chosen arbitrarily, and this region should be viewed only as a sketch of the possible topology for the phase diagram. According to [57Nis], g is a stoichiometric compound. According to [76Mes] and others, however, g has a wide composition range to the Pt-rich side of stoichiometry, and the maximum solubility of Ti in the disordered (Pt) solid solution is only between 11 and 13 at.%. Moreover, [65Pie] discovered an additional ordered phase, TiPt8, with a structure similar to that of TiAu4. TiPt8 was said also to occur over an unspecified homogeneity range. The existence of TiPt8 has been verified by other investigators. [68Kra] observed that the superlattice lines of TiPt8 disappear above 1100 C. In Ti-rich alloys, the cph phase (aTi) can form martensitically from (bTi) during quenching. [60Sat] measured the temperature of the martensite transformation on cooling, which decreased from about 882 C in pure Ti to about 750 C at 2.5 at.% Pt. Between 2.5 and 5 at.% Pt, it remained constant at about 750 C. 57Nis: H. Nishimura and T. Hiramatsu, Nippon Kinzoku Gakkaishi, 21, 469-473 ( 1957). 60Sat: T. Sato, S. Hukai, and Y.C. Huang, J. Austr. Inst. Met., 5(2) 149-153 ( 1960). 65Pie: P. Pietrokowsky, Nature, 206, 291 (1965). 68Kra: P. Krautwasser, S. Bhan, and K. Schubert, Z. Metallkd., 59(9), 724-729 ( 1968). 69Sin: A.K. Sinha, Trans. AIME, 245, 237-240 (1969). 70Don: H.C. Donkersloot and J.H.N. Van Vucht, J. Less-Common Met., 20, 83-91 ( 1970). 76Mes: P.J. Meschter and W.L. Worrell, Metall. Trans. A, 7, 299-305 (1976). Published in Phase Diagrams of Binary Titanium Alloys, 1987, and Bull. Alloy Phase Diagrams, 3(3), Dec 1982. Complete evaluation contains 2 figures, 5 tables, and 21 references. Special Points of the Ti-Pt System