The effect of hBN additive on the microstructure and mechanical properties of sialon ceramics

While ceramic cutting tools currently offer significant advantages, the complex microstructure and inherent grain growth mechanism of ceramic materials severely limits their application. In this work, Y_m/3Si_12-(m+n)Al_m+nO_nN_16-n (Sialon, m = 1.2, n = 1.0) ceramics with hexagonal boron nitride (hBN) additive were fabricated by spark plasma sintering. The effect of the particle size and the content of hBN on the microstructure, the hardness, and the fracture toughness of Sialon ceramics have been investigated. The results indicate that the properties of hBN/Sialon materials initially improve followed by a decline as the hBN particle size increases, with the optimal performance observed at a medium particle size (4–6 μm). hBN particulates within Sialon grains, intergranular Y-rich glassy phases and fibrous carbon-rich Sialon-C whiskers were observed. As the hBN doping content increased, both the hardness and fracture toughness of the material decreased, which is attributed to weak interfacial cracking, crack coalescence, and stress-concentration-induced whisker failure by the complex microstructure. The best-performing sample was doped with 2 wt% of 4–6 μm hBN, achieving a hardness of 25.1 GPa and a fracture toughness of 5.0 MPa·m^1/2.