Microstructure and Properties of Si-Ti-C-O Fiber-Bonded Ceramics.

Abstract

The microstructure and mechanical properties of Si-Ti-C-O fiber-bonded ceramics (Tyrannohex (R)) produced by hot-pressing pre-oxidized Si-Ti-C-O fibers with a surface oxide (SiO2 and TiO2) layer of 250, 430 and 580nm thickness were investigated. The hot-pressing temperature and pressure were 2023K and 50MPa, respectively. Tyrannohex, which was produced using the pre-oxidized fiber with a surface oxide layer of 250nm thickness, showed a close-packed structure with 90% of volume fraction (Vf) of the fiber. The interstices were packed by an oxide material, which existed on the surface of the raw fiber. It was observed that the oxide material changed to TiC-particle dispersed structure by a reaction between TiO2, which existed on the fiber's surface, and excess carbon in the fiber during hot-pressing. Moreover, an interfacial carbon layer (10-20nm) around the fiber was formed. Tyrannohex showed very high fracture energy (8900J/m2) by Chevron notched beam method. Tyrannohex (Vf=90%) showed elastic fracture behavior without any plasticity even at 1673K, because all the fibers were restricted by the close-packed structure. At all the contact points of the fibers, an interfacial carbon layer existed without oxide material. About 90% of the initial strength was maintained after heat-treatment in air for 1000 hours because of an effective formation of a protective oxide layer on the surface.