Effects of h-BN additive on the microstructure and mechanical properties of AlN-based machinable ceramics

The effect of hexagonal boron nitride (h-BN) content on microstructure, mechanical properties, R-curve behavior and machinability of aluminum nitride (AlN) ceramics was investigated. The relative density of sintered compact decreased with increasing h-BN content. The four-point flexural strength also decreased with increasing h-BN content, mainly due to the much lower Young's modulus of BN compared to AlN. AlN–h-BN composites showed a slowly rising R-curve behavior owing to the presence of h-BN platelets, which increased the crack bridging and deflection. During end-milling processes, measured feed and thrust forces decreased with increasing h-BN content, demonstrating an excellent machinability of the composites.