Thermomechanical Performance of Si-Ti-C-O and Sintered SiC Fiber-Bonded Ceramics at High Temperatures

Abstract

The stress-temperature-lifetime response of Si-Ti-C-O fiber-bonded ceramic (Tyrannohex™) and sintered SiC fiber-bonded ceramic (SA-Tyrannohex™) materials were investigated in air from 500° to 1150°C and 500° to 1400°C, respectively. The apparent threshold stress of Si-Ti-C-O fiber-bonded ceramic was about 175 MPa in the 500-1150°C temperature range. When the applied stress of the sintered SiC fiber-bonded ceramic was below an apparent “threshold stress” (e.g., ~225MPa) for tests conducted ≤1150°C, no failures were observed for lifetimes up to ≥1000h. In the case of sintered SiC fiber-bonded ceramic, at the temperature of ≥1300°C, the apparent threshold stress decreased to 175 MPa. The decrease in strength seemed to be caused by grain growth which was confirmed from the SEM fractography. Both fiber-bonded ceramics exhibited much higher durability than a commercial SiC/SiC composite at temperatures above 500°C. In addition, results suggested that the sintered SiC fiber-bonded ceramic (SA-Tyrannohex) is more stable than a Hi-Nicalon/MI SiC composite with BN/SiC fiber coating at temperatures above 1300˚C.