Synthesis of coatings on SiC fibers and their effects on microstructure and mechanical properties of SiCf/SiBCN composites

In this study, the amorphous C, ZrB2, and BN single-layer coatings as well as C/BN, C/ZrB2, ZrB2/BN, and C/ZrB2/BN composite coatings were prepared on SiC fibers (SiCf) by an in situ synthesis and solution impregnation-pyrolysis method. Subsequently, SiCf/SiBCN composites were fabricated by hot-pressing sintering at 1900celcius/60 MPa/30 min to explore the influence of different coatings on the microstructure and mechanical performance of resulting composites. After the preparation of single-layer-coated SiCf, the SiCf(BN) or SiCf(ZrB2) tended to be overlapped with each other, whereas the dispersion of amorphous C-coated SiCf was satisfying. Besides, some uneven areas and attached particles have appeared on fiber surfaces of the SiCf(BN) or SiCf(ZrB2), whereas smooth and dense surfaces of amorphous C-coated SiCf were observed. Because the uniformity of ZrB2 coatings can be partially damaged by the subsequent coating process of BN, the composite coatings of ZrB2/BN and C/ZrB2/BN were thereby not suitable for strengthening SiBCN matrix. The SiCf/SiBCN composites with C/ZrB2 coatings have desirable comprehensive mechanical properties. Nevertheless, the conventional toughening mechanisms such as fiber pull-out and bridging, and crack deflection are not available for these composites because the serious crystallization of SiCf leading to great strength loss, resulting in catastrophic brittle fracture.

Automated summary

Different coatings were applied to SiC fibers to fabricate SiCf/SiBCN composites, with C/ZrB2 coatings showing desirable comprehensive mechanical properties. However, ZrB2/BN and C/ZrB2/BN composite coatings were not effective for reinforcing the SiBCN matrix.