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A ductile ceramic eutectic composite with high strength at 1,873 K

Nature volume 389, pages 49–52 (1997)Cite this article

Monolithic ceramics are not widely used as structural materials because of their brittleness. Ceramic matrix composites, in which whiskers1,2,3 or fibres4,5,6,7 of strong ceramics such as silicon carbide or silicon nitride are embedded in a ceramic matrix, offer improved toughness and strength because the energy of cracks may be dissipated at the whisker/matrix interface. Here we describe a strong ceramic composite with a different kind of microstructure, made by unidirectional solidification of an Al2O3/GdAlO3 eutectic mixture. This composite has a microstructure in which continuous networks of single-crystal Al2O3 and single-crystal GdAlO3 interpenetrate without grain boundaries. Rather than brittle fracture, the material displays plastic deformation at 1,873 K owing to dislocation motion, as in metals. The high strength and resistance to brittle failure of this material at such high temperatures augurs well for applications in mechanical engineering.

Microstructural studies on an Al2O3/Y3Al5O12 (YAG) system using the Bridgman method show that the microstructure of this composite can be controlled by unidirectional solidification8. It has been reported that a unidirectionally solidified Al2O3/YAG eutectic composite has superior flexural strength, thermal stability and creep resistance at high temperature9,10,11, and is a candidate for a high-temperature structural material. However, this material contains many grain boundaries or colonies between Al2O3 and YAG, which are expected12 to impair the mechanical properties. Waku et al.13,14,15 have recently fabricated a eutectic composite consisting of single-crystal Al2O3 and single-crystal YAG with neither colonies nor grain boundaries, using a unidirectional solidification. The composite is thermally stable and its flexural strength at room temperature can be maintained up to 2,073 K, which is just below the melting point (∼2,100 K). In addition, the compression creep strength at 1,873 K and a strain rate of 10−4 s−1is ∼13 times higher than that of sintered composites with the same composition, and the material shows neither weight gain nor grain growth even on heating at 1,973 K in air for 250 hours.

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Figure 1: a, SEM image showing the microstructure of a cross-section perpendicular to the solidification direction of the unidirectionally so.
Figure 2: Typical stress–displacement curves in the three-point flexural test at 1,873 K of unidirectionally solidified Al2O.
Figure 3: High-resolution TEM images of the grain boundaries between Al2O3 and GAP phases of sintered composites (a) an.
Figure 4: TEM images showing the dislocation structure of Al2O3 phases (a) and GAP phases (b) at the tensile-str.

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Acknowledgements

We thank M. Suzuki for his assistance in the TEM observations.

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Authors and Affiliations

  1. Ube Research Laboratory, Corporate Research,

    Y. Waku, N. Nakagawa, T. Wakamoto, H. Ohtsubo, K. Shimizu & Y. Kohtoku

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Waku, Y., Nakagawa, N., Wakamoto, T. et al. A ductile ceramic eutectic composite with high strength at 1,873 K. Nature 389, 49–52 (1997). https://doi.org/10.1038/37937

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