The microstructure and mechanical properties of silicon carbide fibers with boron nitride interphase

Abstract

The 2nd generation SiC tows is a type of essentially polycrystalline fibers (SiC1.46O0.03). Smooth and uniform boron nitride interphase was deposited on SiC fibers by low pressure chemical vapor infiltration (CVI). The scanning electron microscopy(SEM) was used to characterize the microstructure of the BN interphase and fibers while X-ray diffraction(XRD) and TEM were used to characterize the phase constitute of the fibers. The XRD and TEM results showed that the BN interphase prepared by CVI is turbostratic. The effects of thickness on the mechanical properties of SiC fibers were investigated by using two-parameter Weibull distribution. The fibers with thin BN interphase showed higher strength than the as-received fibers, for healing the surface flaws. However, the soft nature of increasing BN thickness had a more dominant effect and resulted in the decrease of fiber strength.