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Iron Aluminide Composites

Published online by Cambridge University Press:  10 February 2011

J. H. Schneibel
J. H. Schneibel*
Affiliation:
Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6115, [email protected]
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Abstract

Iron aluminides with the B2 structure are highly oxidation and corrosion resistant. They arethermodynamically compatible with a wide range of ceramics such as TiC, WC, TiB2, and ZrB2. Inaddition, liquid iron aluminides wet these ceramics very well. Therefore, FeAI/ceramic compositesmay be produced by techniques such as liquid phase sintering of powder mixtures, or pressureless meltinfiltration of ceramic powders with liquid FeAl. These techniques, the resulting microstructures, andtheir advantages as well as limitations are described. Iron aluminide composites can be very strong.Room temperature flexure strengths as high as 1.8 GPa have been observed for FeAl/WC. Substantialgains in strength at elevated temperatures (1073 K) have also been demonstrated. Above 40 vol.% WCthe room temperature flexure strength becomes flaw-limited. This is thought to be due to processingflaws and limited interfacial strength. The fracture toughness of FeAl/WC is unexpectedly high andfollows a rule of mixtures. Interestingly, sufficiently thin (<1 μm) FeAl ligaments between adjacentWC particles fracture not by cleavage, but in a ductile manner. For these thin ligaments the dislocationpile-ups formed during deformation are not long enough to nucleate cleavage fracture, and theirfracture mode is therefore ductile. For several reasons, this brittle-to-ductile size transition does notimprove the fracture toughness of the composites significantly. However, since no cleavage cracks arenucleated in sufficiently thin FeAl ligaments, slow crack growth due to ambient water vapor does notoccur. Therefore, as compared to monolithic iron aluminides, environmental embrittlement is dramaticallyreduced in iron aluminide composites.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 552: Symposium KK – High-Temperature Ordered Intermetallic Alloys VIII , 1998 , KK4.4.1
Copyright
Copyright © Materials Research Society 1999

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References

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