The effect of h-BN content on mechanical properties, microstructure and machinability of hot-pressed h-BN/Si3N4 composites

Si3N4 ceramics now face new applications and challenges in the semiconductor field. The preparation of h-BN/ Si3N4 machinable ceramics incorporating 5-30 vol% h-BN via hot-pressing was carried out. This study systematically explored how the varying h-BN content influenced the composite's microstructure, mechanical attributes, and machinability. The results showed that some of the h-BN was encapsulated by growing Si3N4 grains to form an intragranular structure during the process of hot-pressing, while the remaining h-BN exhibited uniform distribution along grain boundaries. The Si3N4 phase transition in composites was inhibited by excessive hBN, accompanied by a higher decrease in densification. The sample containing 20 vol% h-BN exhibited the best comprehensive performance, with high mechanical strength and excellent machinability. The bending strength and fracture toughness remained high at 862 MPa and 10.3 MPa m1/2, and could be effortlessly machined with cemented carbide drills. Additionally, the machinability of the composites was systematically characterized through observations of crack propagation paths, fitting of R-curves, and mechanical drilling tests.