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

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. (C) 2020 Elsevier B.V. All rights reserved.