Effect of Zr content on microstructure and performance of polycrystalline SiC fiber

Herein, a polycrystalline SiC fiber with a controlled composite containing Zr and B is reported. These polycrystalline fibers are fabricated at a low temperature (1400 °C) using an organic silicon polymer through the polymer-derived ceramic route. The evolution in morphology and microstructure is studied by FTIR spectra, SEM and XRD during the conversion of the polymer fiber into a polycrystalline SiC fiber. The effects of Zr on mechanical properties and microstructure of these polycrystalline SiC fibers are investigated. During sintering, ZrO₂ and ZrB₂ are generated, effectively inhibiting the β-SiC crystallization. The structural morphology results indicate that excessive heteroelement content (> 3 wt%) can lead to surface defects that are not conducive to mechanical properties. The as-fabricated fibers with 2 wt% Zr exhibit dense and smooth surfaces. After the sintering process, a strength enhancement of ~ 26% is observed for the resulting fibers. In addition, the effect of Zr content in fibers on melt spinning, oxidation curing and heat treatment as well as the underlying mechanisms for the beneficial effects of Zr on the mechanical properties of the SiC fibers was investigated. Combined with high mechanical properties and low-temperature heat treatment, these composite fibers open a new strategy to fabricate thermostructural materials.