Crystalline structure in SiC fibers driven by pyrolysis temperature and time

Abstract

In this work, we study the impact of pyrolysis temperature and time on the crystalline structure of lab made silicon carbide (SiC) fibers and their mechanical properties. The polycrystalline structure and the characteristic length scales of β-SiC in fibers were characterized with X-ray diffraction, transmission electron microscope and synchrotron small angle X-ray scattering. The sizes of crystallites, particles and interparticle distance all increase as pyrolysis temperature or time increases while the crystallinity nearly remains constant, indicating SiC crystals in the fiber grow by absorbing the surrounding small crystals. The crystal growth follows the Ostwald ripening when pyrolysis temperature reaches 1500°C. At this temperature, longer pyrolysis time seems to reduce the tensile strength, but still keep increasing the modulus. The stiffness is possibly associated with the growth of particle size, interparticle distance and the size of voids in fibers.