Calculated ternary diagram of Ti–Al–Si system

Author： de Farias Azevedo C.R. Flower H.M.

ISSN： 1743-2847

Source： Materials Science and Technology, Vol.16, Iss.4, 2000-04, pp. : 372-381

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Abstract

The phase equilibria between β (body centred cubic, bcc), α (hexagonal closed packed, hcp), Ti₃ Al–α₂ (hcp), and Ti₅ Si₃ (hcp) in the Ti–Al–Si system have been investigated in the temperature range 700–1200°C. Isothermal sections of the ternary phase diagram have been assessed employing thermodynamic software, which uses the compound energy model to describe the phases mathematically. Available experimental phase equilibria results on the Ti–Al–Si system were used to calculate missing binary and ternary interaction parameters and assess isothermal phase diagrams. Extrapolations in the resulting tie triangles indicate the existence of three eutectoid reactions in the Ti rich corner of the ternary diagram: β → α + Ti₅ Si₃ , α → α₂ + Ti₅ Si₃ , and β → α₂ + Ti₅ Si₃ . Additionally, extrapolations in the β + α₂ + α tie triangle observed at 1100°C indicate that two possibilities arise to represent a peritectoid reaction involving α, β, and α₂phases: β + α₂ → α and β + α → α₂ , depending on the alloy composition and the effect of temperature on the solubitlity of Si in the α phase.