MORPHOLOGY OF POLYMER-DERIVED SiC FIBERS IN Si₃N₄MATRIX

Abstract Polymer-derived SiC fibers such as Nicalon and Tyranno are expected for the reinforcements of ceramic matrix composites. However, there is a problem that the tensile strength of these fibers decreases rapidly at the heat treatment temperature above 1573K. We have studied the pyrolytic process of these fibers at high temperature in an inert gas atmosphere. In this work, we investigated the variation of morphology of the fiber in Tyranno chopped fiber/Si3N4 pressureless-sintered at 1973K in N2. The fiber pullout was observed in the fracture surface of the composite, and the fiber surface was relatively smooth. The morphology of Tyranno fibers in the Si3N4 matrix scarcely changed in the comparison with that of the fibers heat-treated in N2 atmosphere. The fiexural strength and fracture toughness of this composite became higher than those of monolithic Si3N4. The Tyranno fibers are considered to be promising for reinforcement fibers of ceramic matrix composites.