FIBROUS MONOLITHIC CERAMICS .1. FABRICATION, MICROSTRUCTURE, AND INDENTATION BEHAVIOR

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 separated by thin second-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.