Fibrous Monolithic Ceramics: I, Fabrication, Microstructure, and Indentation Behavior |
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Authors: | Suresh Baskaran Stephen D Nunn Dragan Popovic John W Halloran |
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Affiliation: | Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109 |
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Abstract: | Monolithic ceramics have been fabricated from coated green fibers to create fibrous microstructures. The fibrous monoliths consist of high aspect ratio polycrystalline regions (cells) of a primary phase regions (cell boundaries) designed to improve fracture resistance. The cells are the remnants of the green fiber which consists of ceramic powder and a polymer binder. The coating applied on the green fiber forms the cell boundaries. Fabrication and microstructure are described for fibrous monoliths in the SiC/graphite, silicon nitride/BN, alumina/alumina–zirconia, alumina/aluminum titanate, alumina/nickel and Ce-TZP/alumina–Ce–zirconia systems. The SiC/graphite fibrous monolith displays noncatastrophic failure in flexure, with shear delamination along the weak graphite layers. Indentations in SiC/graphite cause cells to spall, with crack arrest and extrusion of graphite from the cell boundaries. Crack deflection and spalling of cells are also observed in alumina/alumina–zirconia fibrous monoliths. In the Ce-TZP/alumina system, transformed regions around indentations are significantly modified by the alumina-containing cell boundaries. |
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