Effect of heat treatment on the tensile strength and creep resistance of advanced SiC fibers

SiC-based fibers, Hi-Niclaon™, Hi-Nicalon™ type S and Tyranno™-SA, were heat treated at 1300–1900 °C in Ar for 1 h. After heat treatment, room temperature tensile strength and 1-h bend stress relaxation (BSR) at 1400 °C in Ar were evaluated for these fibers. As a result, excellent strength retention was exhibited after heat treatment at temperature up to 1780 °C for the Hi-Nicalon™ type S fiber and up to 1900 °C for the Tyranno™-SA fiber. In contrast, relatively low strength retention was observed for Hi-Nicalon™ fiber heat-treated above 1600 °C. Creep resistance of the as-received fibers was improved by high-temperature heat treatments, especially at temperatures above the fiberʹs processing temperature. The microstructure analysis by means of X-ray diffractometer (XRD) and scanning electron microscopy (SEM) indicated that properties of SiC fibers at elevated temperatures are controlled by crystallite size as well as by other factors.