Effects of the single layer CVD BN interface on mechanical properties of oxide–oxide composites fabricated by a sol–gel process

In order to improve mechanical properties of continuous oxide fiber-reinforced oxide (oxide/oxide) composites by tailoring the fiber/matrix (F/M) interface, amorphous boron nitride (BN) coating was applied to the ALF FB3 fibers by chemical vapor deposition (CVD). Subsequent high temperature heat-treatment could not only enhance the crystalline of the as-processed BN coating, but also contribute to severe fiber degradation. Three dimensional (3D) ALF FB3/oxide composites were fabricated by a sol–gel process using diphasic Al2O3–SiO2 sols as precursor. The interfacial characteristics were determined by scanning electron microscopy (SEM). The effects of BN coating on composite mechanical properties were evaluated by three-point bending test. The results show that the BN interface plays a key role in improving the toughness and strength of the composites. The three-point flexural strength of the composites with BN interface is 81.5 MPa, approximately 1.95 times of that for the composites without BN interface (41.9 MPa). Besides, microstructure analysis reveals that BN coating became porous in final composites due to the hydrolyzation of BN during the sol–gel process.