Фазовая диаграмма системы Ir-Ti

К оглавлению: Другие диаграммы (Others phase diargams)

Ir-Ti (Iridium-Titanium) J.L. Murray The major investigations of the Ti-Ir system are [62Cro], [70Ere], and [ 77Kan]. For the high-temperature, Ir-rich portion of the diagram, further experimental work is needed. The assessed phase diagram was obtained by thermodynamic calculations. Melting point data were obtained by [62Cro] using thermal analysis and the gradient technique and by [70Ere] and [72Ere] using the Pirani-Alterthum ( optical) method. [62Cro] estimated liquidus temperatures as the temperatures of sample collapse in thermal gradient experiments. [70Ere] placed an upper bound of 1 at.% on the maximum solubility of Ir in ( aTi), based on metallographic examination of annealed alloys. The reaction ( bTi) = (aTi) + Ti3Ir occurs at approximately 720 C and 5 at.% Ir, based on metallographic and X-ray diffraction work of [77Kan] and not on disagreeing dilatometric [62Cro] and differential thermal analysis [70Ere]. The reaction occurs sluggishly, which explains the failure to detect it by differential thermal analysis. Using X-ray diffraction, [76Jun] found that the single-phase Ti3Ir region at 800 C extends from 25 to 27 at.% Ir. Ti3Ir melts by the peritectic reaction L + Ti3Ir = bTiIr. [62Cro] and [70Ere] agreed in their placement of the peritectic temperature. The homogeneity range of bTiIr was determined by metallographic examination of equilibrated alloys [62Cro, 70Ere]. For alloys containing less than 40 at.% Ir, bTiIr remains stable down to room temperature [70Ere]. The transformation between bTiIr and aTiIr at the high-Ir side of the diagram occurs at approximately 1750 C on cooling [62Cro, 70Ere]. [70Ere] found that TiIr3 has a homogeneity range of 73 to 77 at.% Ir at all the temperatures investigated (1500 to 2000 C). Based on microstructural evidence, [62Cro] and [70Ere] reported that TiIr3 is formed from the liquid by a peritectic reaction. However, there is a large discrepancy in their reported peritectic temperatures-2115 C [62Cro] and 2315 C [70Ere]. [62Cro] bracketed the solubility of Ti in (Ir) between 10 and 15 at.% in the temperature range 1200 to 1850 C. [70Ere] further bracketed the solubility between 7.5 and 12.5 at.% in the temperature range 1500 to 2000 C. Both [70Ere] and [77Kan] placed the maximum Ir content for the martensitic ( bTi) to (aTi) transformation between 2 and 5 at.% Ir. w appears as a transitory phase during the transformation of metastable single-phase b alloys to two-phase (aTi) + (bTi). [77Kan] observed w phase in a 5 at.% Ir alloy, quenched from the (bTi) field and aged at 570 C. w was not observed in a 2 at. % Ir alloy similarly heat treated. 62Cro: J.G. Croeni, C.E. Armantrout, and H. Kato, U.S. Bureau of Mines, Rep. Invest. 6079 (1962). 70Ere: V.N. Eremenko and T.D. Shtepa, Izv. Akad. Nauk SSSR, Met., (6), 198-203 (1970) in Russian; TR: Russ. Metall., (6), 127-130 (1970). 72Ere: V.N. Eremenko and T.D. Shtepa, Colloq. Int. CNRS, (205), 403-413 (1972) in German. 76Jun: A. Junod, R. Flukiger, and J. Muller, J. Phys. Chem. Solids, 37, 27-31 ( 1976) in French. 77Kan: V. Kandarpa, L.R. Cornwell, and K.A. Gingerich, Microstructure Sci., 5, 383-393 (1977). Published in Phase Diagrams of Binary Titanium Alloys, 1987. Complete evaluation contains 2 figures, 6 tables, and 18 references. Special Points of the Ti-Ir System