Microstructure and properties of monazite (LaPO4) coated saphikon fiber/alumina matrix composites

The objective of this research was to engineer a weak interfacial bond in s ingle crystal alpha-alumina (Saphikon) fiber/polycrystalline alumina matrix composites by incorporating a monazite (lanthanum phosphate, LaPO4) coatin g onto Saphikon fibers via sol-gel dip process. Uniaxial hot pressing was u sed to densify LaPO4-coated Al2O3 fiber in an Al2O3 matrix composites. Char acterization of the composites was done by optical microscopy, SEM (scannin g electron microscopy), EDS (energy dispersive spectrometer), indentation t ests, three-point bend and fiber pushout tests. The results showed that the Saphikon fiber/monazite interface was weaker than the polycrystalline alum ina/monazite interface. Crack deflection, interfacial debonding and fiber p ullout occurred at this interface. This was attributed to the fact that the Saphikon fiber/monazite interface was smoother than the monazite/polycryst alline alumina matrix interface. Monazite coating obtained by sol-gel dip c oating method withstood high fabrication temperatures (1400 degrees C) and was conducive to the toughness properties of the composites. (C) 2000 Elsev ier Science Ltd. All rights reserved.