Mk. Cinibulk et Rs. Hay, TEXTURED MAGNETOPLUMBITE FIBER-MATRIX INTERPHASE DERIVED FROM SOL-GELFIBER COATINGS, Journal of the American Ceramic Society, 79(5), 1996, pp. 1233-1246
A calcium hexaluminate (CaAl12O19, 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 w
ere 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 reaction
s and phase transformations contributed to texture formation on alumin
a substrates, The alumina fibers and plates seeded the phase transform
ation of sol-derived transition aluminas to alpha-Al2O3. CaAl12O19 and
CaAl4O7 formed between the seeded alpha-Al2O3, and CaAl4O7 later reac
ted with the seeded alpha-Al2O3 to form CaAl12O19, resulting in a sing
le-phase coating. Several different mechanisms may be responsible for
the texture. The microstructure, phase evolution, and possible mechani
sms for texture formation of CaAl12O19 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.