Microstructure observation and analysis of 3D carbon fiber reinforced SiC-based composites fabricated through filler enhanced polymer infiltration and pyrolysis

3D C/SiC-BN composites were fabricated by filler enhanced polymer infiltration and pyrolysis (FE-PIP) through in situ conversion of active filler boron into h-BN in the high temperature treatment process. The bending strengths and microstructures of composites were studied here. Interphase layers deposited on the fiber surfaces can prevent the strong bonding between fiber reinforcements and composite matrix and repair the defects on the fiber surface, which can improve the bending strength and toughness of composites. The bending stress of C/SiC-BN composites without interphase layer is about 170 MPa while those of composites with PyC or PyC/SiC interphase layers are higher than 300 MPa. Some large pores were left in the interwoven zones while intra-bundle zones were relatively dense, only a small amount of micro-pores could be observed. It could also be concluded that the length of pulled-out fibers was much longer and the pulled-out fiber surface was smoother when interphase layers were deposited. Because the matrix derived from the pyrolysis of slurries adheres to the fiber bundles, some phases with layered structures could be observed in the matrix near the reinforcements. The microstructure evolution of 3D fiber reinforced ceramic matrix composites were also analyzed in this work based on the observation of both 3D C/SiC-BN composites and 3D C/SiC composites fabricated by FE-PIP, where boron and SiC particles were applied as active fillers and inert fillers respectively.