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

In this study, silicon nitride (Si 3 N 4 ) 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 Si 3 N 4 ceramics were investigated. It was found that both flexural strength and fracture toughness of Si 3 N 4 were improved when sintering temperature increases. Moreover, α-Si 3 N 4 phase could transform into β-Si 3 N 4 phase completely when sintering temperature rises to 1800 °C and above. BNNTs can enhance the fracture toughness of Si 3 N 4 dramatically, which increases from 7.202MPa·m 1/2 (no BNNTs) to 10.402MPa·m 1/2 (0.802wt.% BNNTs). However, excessive addition of BNNTs would reduce the fracture toughness of Si 3 N 4 . Meanwhile, the flexural strength and relative density of Si 3 N 4 decreased slightly when BNNTs were added. The related toughening mechanism was also discussed.