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Gamma-Titanium Aluminide Reinforced with A12O3 and TiB2 Fibers*

  • Darrell Dixon (a1) and Joseph W. Newkirk (a2)

Abstract

A two-phase Ti-47Al-2Ta composite reinforced with a titanium diboride (TiB2) and two alumina fibers was processed by hot isotatic pressing and heat treated to simulate service conditions. Diffusion couples were heat treated between 593°C and 982°C for up to 500 h and analyzed using a scanning electron microscope and energy dispersive x-ray spectroscopy.

The fibers used were 3M® alumina, Sapphikon® sapphire, and Textron Specialty Materials TiB2. Observations reveal reaction layers, cracking fibers due to thermal stress, and chemical interactions between ternary addition of Ta with the fibers. Alumina is thermodynamically stable in TiAl, and its coefficient of thermal expansion closely matches TiAl. Observations revealing alumina as a good potential reinforcement in TiAl are discussed. Thermodynamic information supports TiB2 stability in two-phase TiAl. A three-fold increase of Ta at the fiber/ matrix interface of TiB2 is evidence of a lack of homogeneity due to Ta mobility. This indicates a possible loss of oxidation resistance provided by the Ta addition.

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References

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1. Kim, Y.-W., Journal of Metals, pp. 2429, (July 1989).
2. Newkirk, J., and Dixon, D.J., Material Science and Engineering, A153, pp. 662667(1992).
3. Saqib, M., Weiss, I., Mehrotra, G.M., Clevenger, E., Jackson, A.J., and Lipsitt, H.A. Metallurgical Transactions A, Vol. 22A, pp. 17211728 (August, 1991).
4. Misra, A.K., Metallurgical Transactions A, Vol. 22A, p. 715 (March, 1991).

Gamma-Titanium Aluminide Reinforced with A12O3 and TiB2 Fibers*

  • Darrell Dixon (a1) and Joseph W. Newkirk (a2)

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