Paper number 758

EFFECTS OF HIGH TEMPERATURE ARGON HEAT TREATMENT ON TENSILE STRENGTH AND MICROSTRUCTURE OF BN/SIC COATED SIC FIBER PREFORMS

Ramakrishna T.Bhatt¹, and Yuan L Chen²

1Vehicle Technology Center, U.S. Army Research Laboratory
Glenn Research Center, 21000 Brookpark Rd, Cleveland, OH 44135, U.S.A
2Dynamics Engineering Corporation Incorporated
Glenn Research Center, 21000 Brookpark Rd, Cleveland, OH 44135, U.S.A

Summary

Preforms of BN/SiC coated Hi-Nicalon and Sylramic SiC fibers were heat treated under 0.1 MPa argon pressure between 10000 to 18000°C for 1 and 100h. The effects of argon exposure on physical dimensions, weight, room temperature tensile strength, and microstructure of preforms have been studied. Both preforms showed shrinkage and weight loss, and microstructural changes beyond 10000°C. After 100 hr exposure, the Hi- Nicalon preforms showed strength degradation beyond 12000°C. The mechanisms of the strength degradation appear to be grain growth of the SiC fibers and crystallization of the BN coating. After 100 hr, the Sylramic preforms heat treated to 10000°C retained their as-produced strength while some of those heat-treated between 10000 and 18000°C showed strength degradation and others did not. At 18000°C, the ultimate tensile strength decreased with increasing time of exposure. Reasons for strength degradation of Sylramic preforms are being investigated.

Keywords

SiC fibers, preform, microstructure, tensile strength, BN/SiC interface.