Evaluation of microstructure and phase relations in a powder processed Ti-44AI-12Nb alloy

  • S. G. Kumar
  • R. G. Reddy
  • J. Wu
  • J. Holthus


Titanium aluminides based on the ordered face-centered tetragonal γTiAI phase possess attractive properties, such as low density, high melting point, good elevated temperature strength, modulus retention, and oxidation resistance, making these alloys potential high-temperature structural materials. These alloys can be processed by both ingot metallurgy and powder metallurgy routes. In the present study, three variations of the powder metallurgy route were studied to process a Ti-44Al-12Nb (at. %) alloy: (a) cold pressing followed by reaction sintering (CPprocess); (b) cold pressing, vacuum hot pressing, and then sintering (HP process); and (c) arc melting, hydride-dehydride process to make the alloy powder, cold isostatic pressing, and then sintering (AM process). Microstructural and phase relations were studied by x-ray diffraction (XRD) analysis, optical microscopy, scanning electron microscopy with an energy-dispersive spectrometer (SEM-EDS), and electron probe microanalysis (EPMA). The phases identified were Ti3AI and TiAl; an additional Nb2AI phase was observed in the HPsample. The microstructures of CPand HP processed samples are porous and chemically inhomogeneous whereas the AM processed sample revealed fine equiaxed microstructure. This refinement of the microstructure is attributed to the fine, homogeneous powder produced by the hydride-dehydride process and the high compaction pressures.


microstructure phase relations powder metallurgy titanium alloy 


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  1. 1.
    W.B. Pearson,A Handbook of Lattice Spacings and Structures of Metals and Alloys, Vol 2, Pergamon Press, 1967, p 126Google Scholar
  2. 2.
    J.R. Groza, S.H. Risbud, and K. Yamazaki,Proc. Plasma Synthesis and Processing of Materials, K. Upadhya, Ed., TMS, 1993, p 85–93Google Scholar
  3. 3.
    F.H. Froes,C. Suryanarayana, and D. Elizer,J. Mater Sci., Vol 27, 1992, p 5113–5140CrossRefGoogle Scholar
  4. 4.
    D.P. Pope,Proc. High Temperature Aluminides and Intermetallics, S.H. Whang, C.T. Liu, D.R Pope, and J.O. Stiegler, Ed., TMS, 1992, p 51–61Google Scholar
  5. 5.
    Y Nishiyama, T. Miyashita, S. Isobe, and T. Noda,Proc. High Temperature Aluminides and Intermetallics, S.H. Whang, C.T. Liu, D.R Pope, and J.O. Stiegler, Ed., TMS, 1991, p 557–584Google Scholar
  6. 6.
    R.G. Rowe,Adv. Mater Proc, Vol 141 (No. 3), 1992, p 33Google Scholar
  7. 7.
    YW. Kim,J. Met., July 1989, p 24–30Google Scholar
  8. 8.
    T. Tsujimoto and K. Hashimoto,Proc. High Temperature Ordered Intermetallic Alloys III, Vol 133, C.T. Liu, A.I. Taub, N.S. Stoloff, and C.C. Koch, Ed., MRS, 1989, p 391–396Google Scholar
  9. 9.
    S.G. Kumar and R.G. Reddy,Proc. Extractive Metallurgy of Copper Nickel and Cobalt, R.G. Reddy and R.N. Weizenbach, Ed., TMS, 1993, p 1101–1123Google Scholar
  10. 10.
    J.H. Moll, C.F. Yolton, and B.J. McTiernan,Int. J. Powder Metall.,Vol 26 (No.2), 1990, p 149–155Google Scholar
  11. 11.
    R.E. Schafrik,Metall. Trans. B, Vol 7, 1976, p 713–716CrossRefGoogle Scholar
  12. 12.
    G.-X. Wang and M. Dahms,Metall. Trans. A, Vol 24, 1993, p 1517–1526CrossRefGoogle Scholar
  13. 13.
    F.H. Froes, D. Eylon, and C. Suryanarayana,JOM, Vol 42 (No. 3), 1990, p 26CrossRefGoogle Scholar
  14. 14.
    S.G. Kumar and R.G. Reddy, unpublished researchGoogle Scholar
  15. 15.
    R.G. Reddy and K.N. Hebbar,Proc. Electron Beam Melting and Refining—State of the Art 1991, R. Bakish, Ed., Bakish Materials Corporation, 1991, p 248–291Google Scholar
  16. 16.
    D.M. Kocherginsky and R.G. Reddy,Proc. Control of Interfaces in Metal and Ceramic Composites, R.Y Lin and S.G. Fishman, Ed., TMS, 1994, p71–79Google Scholar
  17. 17.
    S.G. Kumar, R.G. Reddy, and L. Brewer,J. Phase Equilibria, Vol. 15 (No. 3), June 1994, p. 279–284CrossRefGoogle Scholar
  18. 18.
    U.R. Kattner, J.-C. Lin, and YA. Chang,Metall. Trans. A, Vol 23, 1992, p 2081CrossRefGoogle Scholar
  19. 19.
    J.A. Graves, J.H. Perepezko, C.H. Ward, and F.H. Froes,Scr. Metall, Vo1 21, 1987, p 567–572CrossRefGoogle Scholar
  20. 20.
    J.J. Milencia, C. McCullough, C.-G. Levi, and R. Mehrabian,Scr Metall., Vol 21, 1987, p 1341–1346CrossRefGoogle Scholar
  21. 21.
    G.E. Fuchs and S.Z. Hayden,Matee Sci. Eng. A, Vol 152,1992, p 277–282CrossRefGoogle Scholar
  22. 22.
    A. Kawabata, T. Tadano, and O. Izumi,Scr Metall., Vo1 22, 1988, p 1725–1730CrossRefGoogle Scholar
  23. 23.
    R Prasad Rao and K. Tangri,Matee Sci. Eng. A, Vo1 132, 1991, p 49–59CrossRefGoogle Scholar
  24. 24.
    C.R. Feng, D.J. Michel, and C.R. Crowe,Mater Sci. Eng. A, Vo1 145, 1991, p 257–264CrossRefGoogle Scholar
  25. 25.
    S. Yamauchi and H. Shiraishi,Mater Sci. Eng. A, Vol 152,1992, p 283–287CrossRefGoogle Scholar
  26. 26.
    FV Lenel,Powder Metallurgy: Principles and Applications, Metal Powder Industries Federation, 1980Google Scholar
  27. 27.
    J.H. Perepezko, YA. Chang, L.E. Seitzman, J.C. Lin, N.R. Bonda, T.J. Jewett, and J.C. Mishurda,Proc. High Temperature Aluminides and Intermetallics, S.H. Whang, C.T. Liu, D.R Pope, and J.O. Stiegler, Ed., TMS, 1991, p 19–47Google Scholar
  28. 28.
    C. Suryanarayana, G.-H. Chen, A. Freier, and F.H. Froes,Mater Sci. Eng. A, Vol 158, 1992, p 93–101CrossRefGoogle Scholar

Copyright information

© ASM International 1995

Authors and Affiliations

  • S. G. Kumar
    • 1
  • R. G. Reddy
    • 1
  • J. Wu
    • 2
  • J. Holthus
    • 2
  1. 1.Department of Chemical and Metallurgical EngineeringUniversity of NevadaRenoUSA
  2. 2.Materials Science Division, Lawrence Berkeley LaboratoriesUniversity of CaliforniaBerkeleyUSA

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