Mechanical properties and machinability of AlN-hBN ceramics prepared by spark plasma sintering

AlN-hBN ceramic composites with 3 mass% CaF2 were fabricated by spark plasma sintering at 1800°C for 10 min. The effects of hBN content on mechanical properties, microstructure, and machinability of AlN-hBN composites were investigated. With increasing hBN content, relative density, flexural strength, and Young's modulus decreased, whereas fracture toughness increased slightly. Vickers' indentation cracks are largely deflected near hBN platelets, implying a weak interfacial bond between the AlN and the hBN. The fracture surfaces of AlN-hBN composites showed a higher tendency of intergranular fracture than monolithic AlN. During end-milling processes, the cutting resistance decreased with hBN content, demonstrating the machinability of AlN ceramic can be improved significantly by the addition of hBN.