Dip-coating of boron nitride interphase and its effects on mechanical properties of SiCf/SiC composites

Boron nitride (BN) coatings were successfully synthesized on KD-1 SiC fibers by dip-coating in boric acid and urea solution followed by heat treatment at 1000 °C in nitrogen. The SEM micrographs indicated that the BN coating is smooth. The XRD and Raman spectrum results showed that the composition of the coatings is h-BN. The effects of BN interphase on the mechanical properties of 2.5D SiC fiber reinforced CVI-SiC matrix (SiC/SiC) composites were investigated. The results show that the flexural strength of SiCf/SiC composites with and without BN interphase is 170 MPa and 60 MPa, respectively. And, compared to composites without interphase, the SiCf/SiC composites with BN interphase exhibit an obvious toughened fracture behavior. It is indicated that dip-coating BN interphase can effectively adjust the interfacial bonding strength and improve the mechanical properties of SiCf/SiC composites.