Effect of complex alloying on the phase composition and oxidation resistance of O-Ti2AlNb based intermetallic alloys

V.M. Imayev, D.M. Trofimov ORCID logo , A.A. Ganeev, R.R. Timiryaev, R.I. Zainullin, M.R. Shagiev, J. Shen, R.R. Mulyukov show affiliations and emails
Received 13 November 2025; Accepted 28 November 2025;
Citation: V. M. Imayev, D. M. Trofimov, A. A. Ganeev, R. R. Timiryaev, R.I. Zainullin, M.R. Shagiev, J. Shen, R. R. Mulyukov. Effect of complex alloying on the phase composition and oxidation resistance of O-Ti2AlNb based intermetallic alloys. Lett. Mater., 2025, 15(4) 440-448
BibTex   https://doi.org/10.48612/letters/2025-4-440-448

Abstract

The mass gain curves obtained for samples of complex alloyed O-Ti2AlNb based alloys isothermally exposed in air at 700°C/600 h.The effect of complex alloying on the phase composition and oxidation resistance of intermetallic alloys based on the Ti2AlNb phase has been studied. The following experimental alloys (in at.%) were investigated: Ti-22Al-25Nb-0.15B, Ti-22Al-21Nb-5.5(Zr, Mo, Ta, Sn, Hf)-0.3Si-0.15B, Ti-25Al-21Nb-5.5(Zr, Mo, Ta, Sn, Hf)-0.3Si-0.15B, Ti-23.5Al-23Nb-4(Zr, Mo, Ta, Hf)-0.3Si and Ti-23Al-25.5Nb-2.5(Zr, Mo)-0.3Si. The first alloy was used as a reference alloy. The complex alloys were alloyed with metallic elements having a high melting point and / or a higher atomic radius in order to improve oxidation and creep resistance, and to provide solid solution strengthening in a wide temperature range. The ratio between Al content and β-stabilization (in Mo-equivalent) of the alloying elements varied around the ratio value corresponding to the ternary Ti-22Al-25Nb alloy. As-cast alloys were annealed at 900°C followed by furnace cooling in order to thermodynamically equilibrate the as-cast ingots. The alloys based on Ti-22Al, Ti-23Al and Ti-23.5Al consisted mostly of two basic phases, O(Ti2AlNb) and β / B2, whereas the complex alloy based on Ti-25Al was near completely single-phase and contained only insignificant amount of the β / B2 phase. The volume fraction of the β / B2 phase in the alloys containing 22 – 23.5 Al was in the range of 17.6 – 27.5 %. Microalloying with boron led to formation of borides but did not refine the as-cast microstructure. DSC analysis showed that for all alloys, the equilibrium phase transformation sequence is as follows: L → β / B2 → β / B2 + α2(Ti3Al) → β / B2 + α2(Ti3Al) + O(Ti2AlNb) → O(Ti2AlNb) + β / B2. The oxidation behavior was evaluated for the annealed conditions of the alloys at 700°C / 600 h. The oxidation resistance increased due to complex alloying, with an increase in the aluminum content and with a decrease in the β / B2 phase content. The highest oxidation resistance showed the alloys based on Ti-25 and 23.5Al. In these alloys, the mass gain after oxidation at 700°C / 600 h was around 0.5 mg / cm2. Potential advantages of the complex alloying of O-Ti2AlNb based alloys are discussed.

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Funding

1. Ministry of Science and Higher Education of the Russian Federation - Контракт ИПСМ РАН №13.2251.21.0285