Moisture behavior and effects on the mechanical properties and the microstructures of SiO2f/Si3N4–BN amorphous composites

Water diffusion in fiber reinforced ceramic composites could reduce the flexural strength as a result of weakened fiber/matrix binding. In the paper, the braided silica fiber reinforced silicon nitride and boron nitride amorphous composites (SiO_2f/Si₃N₄–BN) was prepared through repeated infiltration of hybrid preceramic precursor and pyrolysis at high temperature in ammonia atmosphere. The moisture behavior of the SiO_2f/Si₃N₄–BN composites and moist effects on the mechanical properties and the microstructures of composites were studied. The results showed that the water absorption characteristic of amorphous composites could be described by using the Fick’ law. The flexural strength could be adjusted and the maximal value of that reached 161.7 MPa by controlling moderate relative humidity, which is 58.8% higher more than that of the as-received composites. SEM indicated that good mechanical properties is on the ground of the interface structure change between fiber and matrix and more fibers were pulled out which absorbing much more fracture energy.