Interdepartmental analytic center, Moscow, Russia:

N. I. Dashkevich, Area manager

National University of Science and Technology “MISiS”, Moscow, Russia:
N. A. Belov, Professor, Director of Engineering Center “Casting Technologies and Materials”, e-mail: nikolay-belov@yandex.ru
S. O. Beltyukova, Engineer, Casting Process Technology Chair

The Thermo-Calc program was used for the quantitative analysis of phase diagrams of ternary Al – Ti – X systems (where Х is Nb, Mo, Cr, V, Zr, W, Mn and Si) in the area of gamma-phase alloys on the basis of titanium aluminide TiAl. Isothermal and polythermal cross-sections were calculated together with temperatures of liquidus, solidus and other phase transformations. Isothermal cuts were calculated for the temperatures of 1200 and 800 °C. The first temperature is typical for hot isostatic pressing, and the second one corresponds to the blade operating temperatures. Polythermal cuts were calculated for the concentration of 45% (mol.) of Al, which corresponds to the average content in the well-known gamma-phase alloys. The critical temperatures and phase composition of selected alloys were calculated with this aluminium concentration. The calculation of Al – Ti – X systems in the given ranges has shown the
presence of the following phases:
α — solid solution on the basis of hexagonal close-packed lattice (α-titanium);
β — solid solution on the basis of BCC lattice (β-titanium);
β₂ — solid solution on the basis of BCC lattice (with increased content of β-stabilizer);
γ — solid solution on the basis of TiAl aluminide;
α_2 — solid solution on the basis of Ti₃Al aluminide;
Ti₅Si₃ — titanium silicide;
σ — phase on the basis of AlX₃ compound;
λ — phase on the basis of TiX₂ compound (Laves phase).
There were defined the parameters of nonvariant eutectoid reaction α→α₂+γ+β. According to the calculation, this reaction should proceed in the systems with niobium, molybdenum, chromium, tungsten and manganese. Temperature of this reaction is varied from 1095 °C (in the system Al – Ti – W) to 1036 °С (in Al – Ti – Mn system). There is shown that the phase composition of ternary alloys (including mass fractions of various phases (α, β, γ, α_2, etc.)) and their element concentration (Ti, Al, Х) depend mostly on the heat treatment temperature.
This work was carried out with the support of the Grant of Russian Science Foundation 14-19-01033.

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