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ArticleName Calculation analysis of phase diagrams of ternary Al – Ti – X systems in the area of γ-alloys on the basis of titanium aluminide
DOI 10.17580/tsm.2015.10.06
ArticleAuthor Dashkevich N. I., Belov N. A., Beltyukova S. O.

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:
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;
α2 — 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, α2, 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.

keywords Phase diagrams, titanium aluminides, gamma-phase alloys, isothermal cuts, polythermal cuts, crystallization range, unbalanced crystallization, eutectoid reaction

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