RECENT DEVELOPMENTS OF THE SIC FIBER NICALON AND ITS COMPOSITES, INCLUDING PROPERTIES OF THE SIC FIBER HI-NICALON FOR ULTRA-HIGH TEMPERATURE

Recent developments of the SiC fiber Nicalon(TM) and its composites are reported. The first section concerns the development history and characteristics of the SiC fiber Nicalon, while the second deals with Nicalon-fiber-reinforced PMC, MMC and CMC. There are four grades of Nicalon fiber, namely the ceramic, HVR (high volume resistivity), LVR (low volume resistivity) and carbon-coated Nicalon fiber. The ceramic grade of Nicalon fiber has been investigated in relation to the tensile strength of the fiber after exposure at 800-1400-degrees-C in air. HVR or LVR fiber/epoxy resin composites have low and high dielectric constants, respectively. Nicalon/Al composite wire as an MMC is investigated with respect to tensile strength at high temperatures. The flexural strength, etc., of Nicalon/SiC composite, called Nicaloceram(TM), as a CMC is reported. A Nicalon/borosilicate glass composite used the carbon-coated Nicalon fiber having various thicknesses of the carbon layer, and the effect of the carbon layer thickness on the flexural strength of this composite has been investigated. The third section describes a low-oxygen-content SiC fiber referred to as Hi-Nicalon(TM) for ultra-high temperature use. This SiC fiber with excellent thermal stability has been developed by reducing the oxygen content. Polycarbosilane fiber is cured by electron beam irradiation under a He stream and pyrolyzed in an inert atmosphere. This SiC fiber, Hi-Nicalon, has a continuous, multi-filament form and consists of 0-5 wt % oxygen. It has high tensile strength and tensile modulus of 2.8 and 270 GPa, respectively. Hi-Nicalon has good tensile properties at high temperature. The properties of SiC composites reinforced with Hi-Nicalon have also been investigated.