Effect of BN/SiC Multilayered Interphases on Mechanical Properties of SiC Fibers and Minicomposites by PIP

BN and BN/SiC interphases were deposited on the surface of SiC fibers by CVI process, and the mechanical properties of the as-received and coated fibers were evaluated. SiCf/SiC minicomposites were prepared by PIP using the as-received, BN-coated and BN/SiC coated fiber bundles as reinforcements. The effects of interphases on the mechanical properties of the composites were studied. The results show that the interphases prepared by CVI process are uniform and compact. The deposited BN interphase contains hexagonal phases with small crystal size (1.76 nm). The deposited SiC interphase has better crystallinity and larger grain size (18.73 nm) than BN interphase. The elastic modulus of coated SiC fibers shows basically no change, but the tensile strength decreases. The maximum tensile load and fracture strain of SiCf/BN/SiC and SiCf/(BN/SiC)/SiC minicomposites are significantly increased, in comparison to SiCf/SiC minicomposites. It can be seen from the cross-sections of SiCf/BN/SiC and SiCf/(BN/SiC)/SiC mini-composites that the fibers with interphases pull out obviously relative to SiCf/SiC mini-composites, and the BN interphases played a reinforcing role in the tensile fracture process of the composites. The composites with interphases exhibit obvious fiber pull-out resulting in more energy consumption during the fracture, so that the composite can endure more load.