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

Monolithic ceramics have been fabricated from coated green fibers to c reate fibrous microstructures. The fibrous monoliths consist of high a spect ratio polycrystalline regions (cells) of a primary phase separat ed by thin second-phase regions (cell boundaries) designed to improve fracture resistance. The cells are the remnants of the green fiber whi ch consists of ceramic powder and a polymer binder. The coating applie d on the green fiber forms the cell boundaries. Fabrication and micros tructure are described for fibrous monoliths in the SiC/graphite, sili con nitride/BN, alumina/alumina-zirconia, alumina/aluminum titanate, a lumina/nickel and Ce-TZP/alumina-Ce-zirconia systems. The SiC/graphite fibrous monolith displays noncatastrophic failure in flexure, with sh ear delamination along the weak graphite layers. Indentations in SiC/g raphite cause cells to spall, with crack arrest and extrusion of graph ite from the cell boundaries. Crack deflection and spalling of cells a re also observed in alumina/alumina-zirconia fibrous monoliths. In the Ce-TZP/alumina system, transformed regions around indentations are si gnificantly modified by the alumina-containing cell boundaries.