Yoshikazu Imai

Microstructure and oxidative degradation behavior of silicon carbide fiber Hi-Nicalon type S

Abstract Polycarbosilane-derived SiC fibers, Nicalon, Hi-Nicalon, and Hi-Nicalon type S were exposed for 1 to 100 h at 1273–1773 K in air. Oxide layer growth and tensile strength change of these fibers were examined after the oxidation test. As a result, three types of SiC fibers decreased their strength as oxide layer thickness increased. Fracture origins were determined at near the oxide layer-fiber interface. Adhered fibers arised from softening of silicon oxide at high temperature were also observed. In this study, Hi-Nicalon type S showed better oxidation resistance than other polycarbosilane-derived SiC fibers after 1673 K or higher temperature exposure in air for 10 h. This result was explained by the poreless silicon oxide layer structure of Hi-Nicalon type S.

Thermal stability of the low-oxygen-content silicon carbide fiber, Hi-NicalonTM

Abstract The low-oxygen SiC fiber, Hi-NicalonTM, was prepared by the pyrolysis of polycarbosilane fibers cured with electron-beam irradiation. This SiC fiber is continuous, in multi-filament form, and consists of Si-1.39C-0.010 by atomic ratio. Hi-NicalonTM fiber has a high tensile strength and an elastic modulus of 2.8 and 270 GPa, respectively. This SiC fiber retains high strength and modulus even after exposure for 10 h at 1873 K in argon. It exhibits outstanding thermal stability as compared to other commercially available polymer-derived ceramic fibers.

Properties of polycarbosilane-derived silicon carbide fibers with various C/Si compositions

Abstract SiC fibers with various C/Si compositions have been synthesized by the use of an irradiation-curing process. The polycarbosilane(PCS) fibers were cured by irradiation with an electron beam in a helium atmosphere. After curing, the fibers were pyrolyzed at 1573 K under controlled conditions, and SiC fibers with C/Si of 0.84 to 1.68 were obtained. The chemical composition of the fibers was

Development of SiC/Al composites as low activation materials

A SiC/Al composite using Continuous and multifilament-yarn SiC fibers (Nicalon) was investigated. The objectives of this investigation are to establish industrial basis for a SiC/Al perform wire, to evaluate neutron damage to the composite and to develop a SiC/Al composite for fusion reactor application. Mechanical properties were measured by tensile test, three point bending test and internal friction measurement. Microstructure were inspected by means of SEM, TEM and STEM-EDX. Under optimum conditions, we can obtain an average strength of 1.25 GPa for preform wires. Effects of neutron irradiation were studied using fission neutrons from JOYO and JMTR and with 14 MeV neutrons from RTNS-II. The SiC fibers showed excellent stability in dimensional changes by radiation damage. Increments of tensile strength and Youngs modulus was observed by irradiation in FBR (JOYO).

High-temperature thermal stability of Hi-Nicalon™ SiC fiber/SiC matrix composites under long term cyclic heating

Abstract The high-temperature thermal stability of C-coated standard grade Nicalon™ SiC fiber and of C or BN-coated Hi-Nicalon™ SiC fiber-reinforced SiC matrix composites under long-term cyclic heat exposure in air has been studied. Woven fabric composites fabricated by the PIP process were cyclic heat-exposed at 1273 and 1673 K for up to 1000 h with one heat exposure cycle of 200 h. The degradation of the composites was evaluated by a three-point flexure test at room temperature. The oxidation of the composite occurred from the matrix phase due to the existence of macro- and micro-pores that exist in the matrix. Degradation of the strength was observed for the C-coated SiC fiber/SiC composites after heat exposure for 200 h at 1273 K. On the contrary, the BN-coated Hi-Nicalon™ SiC fiber/SiC composite showed only a slight degradation even after a 1000-h exposure at 1273 K. However, at 1673 K, this composites strength degraded after an 800-h exposure.