Textured magnetoplumbite fiber-matrix interphase derived from sol-gel fiber coatings
- Materials Directorate, Wright-Patterson AFB, OH (United States). Wright Lab.
A calcium hexaluminate (CaAl{sub 12}O{sub 19}, magnetoplumbite structure) sol was used to coat alumina and yttrium-aluminum-garnet (YAG) single-crystal fibers and single-crystal alumina plates. When the coated substrates were either annealed or hot-pressed in polycrystalline alumina and YAG matrices, the calcium hexaluminate basal cleavage planes were aligned parallel with the fiber-matrix interface. A complex series of reactions and phase transformations contributed to texture formation on alumina substrates. The alumina fibers and plates seeded the phase transformation of sol-derived transition aluminas to {alpha}-Al{sub 2}O{sub 3}, CaAl{sub 12}O{sub 19} and CaAl{sub 4}O{sub 7} formed between the seeded {alpha}-Al{sub 2}O{sub 3}, and CaAl{sub 4}O{sub 7} later reacted with the seeded {alpha}-Al{sub 2}O{sub 3} to form CaAl{sub 12}O{sub 19}, resulting in a single-phase coating. Several different mechanisms may be responsible for the texture. The microstructure, phase evolution, and possible mechanisms for texture formation of CaAl{sub 12}O{sub 19} powders, sol-derived thin films, and coated plates and fibers, with and without hot-pressed matrices, were studied and are discussed. Deflection and propagation of cracks within the fiber-matrix interphase in thin foils suggests that such an interphase may protect fibers from matrix cracks.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 253562
- Journal Information:
- Journal of the American Ceramic Society, Vol. 79, Issue 5; Other Information: PBD: May 1996
- Country of Publication:
- United States
- Language:
- English
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