The effect of boron nitride interphase on the thermal stability of SiC fibers

Abstract

The SiC fibers were coated with uniform boron nitride interphase by chemical vapor infiltration (CVI). The as-received and BN-coated fibers were heat-treated in flowing nitrogen for 2 h to investigate the effect of BN interphase on the thermal stability of fibers. Tensile strengths of as-received and BN-coated fibers have been measured at room temperature. The effects of heat-treatment on the tensile strengths of fibers were investigated using Weibull distribution. The results showed the deposited BN interphase has turbostratic structure, with nano crystallites of h-BN randomly orientated. Heat-treatment improved the crystallization degree of BN interphase. The as-received fibers had a tensile strength of 2.56 GPa and a Weibull modulus of 5.39. The BN-coated fibers showed lower tensile strength than the as-received fibers, on account of the increased diameter and soft nature of BN. The average strengths of fibers decreased, and BN-coated fibers showed higher strength retention than as-received fibers at the same heat-treatment temperature due to the protection of BN interphase. The BN interphase acts as a compliant layer, which reduces the thermal damage to SiC fibers during heat-treatment.