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Journal of Phase Equilibria and Diffusion

, Volume 31, Issue 6, pp 561–561 | Cite as

Al-Nb-Ti (Aluminum-Niobium-Titanium)

  • V. Raghavan
Phase Diagram Evaluations

Keywords

Phase Equilibrium Differential Thermal Analysis Cohesive Energy TiAl3 Invariant Reaction 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

The phase equilibria in this system were reviewed earlier by [1993Gam], [2005Rag], and [2005Tre]. More recent results were updated by [2010Rag]. Additional new data from two recent publications [2009Leo, 2009Rio] will be summarized here.

New Results on the Ternary Phase Equilibria

In the earlier literature on this ternary system, the nature of the invariant reaction involving liquid (L), TiAl (γ), Nb2Al (σ) and TiAl3 (η) has been interpreted either as a U-type transition reaction or as a ternary eutectic reaction, see the reviews listed above. [2009Rio] arc-melted under Ar atm two ternary alloys of composition (in at.%): 57.2Al-35.7Nb-7.1Ti and 51.4Al-39.8Nb-8.8Ti. The alloys were annealed at 1510 °C or 1410 °C for 3-4 h and quenched in water. The phase equilibria were investigated with scanning and transmission electron microscopy, x-ray powder diffraction and differential thermal analysis. After a detailed analysis of the microstructures and the measured compositions of the coexisting phases, [2009Rio] concluded that the invariant reaction is of the ternary eutectic type: L ↔ TiAl (γ) + Nb2Al (σ) + TiAl3 (η), with the eutectic composition at 56Al-37.2Nb-6.8Ti (at.%) and the eutectic temperature at 1532 °C.

[2009Leo] studied the decomposition of the B2 (β) phase on ageing in three alloys of nominal composition Nb24Ti40Al, Nb30Ti40Al and Nb36Ti40Al. The alloys were aged at 700 °C for 720, 1080 or 3600 h and quenched in water. The phase structures were studied by x-ray powder diffraction, optical and transmission electron metallography and by selected-area and convergent-beam electron diffraction. Formation of the ω-related P63/mcm, hP18 phase was observed in all the three alloys. For the Nb24Ti40Al alloy, the measured lattice parameters were: a = 0.796 nm and c = 0.557 nm, with the relationship a = a β \( \sqrt{6}\) and c = a β \( \sqrt{3}\). The addition of Nb appears to stabilize the Ti5Ga4-type hP18 structure, in preference to the Mn5Si3-type hP16 structure. Ab initio calculations confirmed the stabilizing effect of Nb, with the calculated cohesive energies in Ti5Al3, Ti5Al4 and Ti5Al3Nb equal to 6.449, 6.215 and 6.927 eV per atom respectively [2009Leo].

References

  1. 1993Gam.
    S. Gama, Aluminum-Niobium-Titanium, Ternary Alloys, Vol 7, G. Petzow and G. Effenberg, Ed., VCH Verlagsgesellschaft, Weinheim, Germany, 1993, p 382-398Google Scholar
  2. 2005Rag.
    V. Raghavan, Al-Nb-Ti (Aluminum-Niobium-Titanium), J. Phase Equilib. Diffus., 2005, 26(4), p 360-368Google Scholar
  3. 2005Tre.
    L. Tretyachenko, Aluminum-Niobium-Titanium, Landolt-Bornstein New Series IV, Vol 11A3, G. Effenberg and S. Ilyenko, Ed., 2005, p 334-379Google Scholar
  4. 2009Leo.
    K.J. Leonard, R. Tewari, A. Arya, J.C. Mishurda, G.K. Dey, and V.K. Vasudevan, Decomposition of the βo Phase to the P63/mcm, hP18 Structure in Nb-(24-36)Ti-40Al Alloys, Acta Mater., 2009, 57, p 4440-4453Google Scholar
  5. 2009Rio.
    O. Rios, D.M. Cupid, H.J. Seifert, and F. Ebrahimi, Characterization of the Invariant Reaction Involving the L, η, γ and σ Phases in the Ti-Al-Nb System, Acta Mater., 2009, 57, p 6243-6250CrossRefGoogle Scholar
  6. 2010Rag.
    V. Raghavan, Aluminum-Niobium-Titanium, J. Phase Equilib. Diffus., 2010, 31(1), p 47-52CrossRefMathSciNetGoogle Scholar

Copyright information

© ASM International 2010

Authors and Affiliations

  1. 1.ChennaiIndia

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