MICROSTRUCTURE AND OXIDATIVE-DEGRADATION BEHAVIOR OF SILICON-CARBIDE FIBER HI-NICALON TYPE-S

Polycarbosilane-derived SiC fibers. Nicalon, Hi-Nicalon, and Hi-Nicalo n type S were exposed for 1 to 100 h at 1273-1773 K in air. Oxide laye r growth and tensile strength change of these fibers were examined aft er the oxidation test. As a result, three types of SIC fibers decrease d their strength as oxide layer thickness increased. Fracture origins were determined at near the oxide layer-fiber interface. Adhered fiber s arised from softening of silicon oxide at high temperature were also observed. In this study, Hi-Nicalon type S showed better oxidation re sistance than other polycarbosilane-derived SIC fibers after 1673 K or higher temperature exposure in air for 10 h. This result was explaine d by the poreless silicon oxide layer structure of Hi-Nicalon type S. (C) 1998 Elsevier Science B.V. All rights reserved.