Fabrication and mechanical properties of boron nitride nanotube reinforced silicon nitride ceramics

In this study, silicon nitride (Si3N4) ceramics added with and without boron nitride nanotubes (BNNTs) were fabricated by hot-pressing method. The influence of sintering temperature and BNNTs content on the microstructures and mechanical properties of Si3N4 ceramics were investigated. It was found that both flexural strength and fracture toughness of Si3N4 were improved when sintering temperature increases. Moreover, α-Si3N4 phase could transform into β-Si3N4 phase completely when sintering temperature rises to 1800 °C and above. BNNTs can enhance the fracture toughness of Si3N4 dramatically, which increases from 7.2 MPa m1/2 (no BNNTs) to 10.4 MPa m1/2 (0.8 wt% BNNTs). However, excessive addition of BNNTs would reduce the fracture toughness of Si3N4. Meanwhile, the flexural strength and relative density of Si3N4 decreased slightly when BNNTs were added. The related toughening mechanism was also discussed.