Machinable Al2O3/BN composite ceramics with strong mechanical properties

Al2O3/BN composite ceramics with nano-sized BN dispersions ranging from 0 to 30 vol.% were successfully fabricated by hot-pressing alpha-Al2O3 powders with turbostratic BN (t-BN) coating, which was prepared through chemical processes using boric acid and urea. SEM observations revealed that the nano-sized hexagonal BN (h-BN) particulates were homogeneously dispersed within Al2O3 grains as well as at grain boundaries. Vickers hardness of materials decreased with an increase in BN content. The fracture toughness was improved but the fracture strength had a small decrease, in comparison to Al2O3 monolithic ceramics. The nanocomposite ceramics with BN content more than 20 vol.% exhibited excellent machinability, which could be drilled using conventional hard metal alloy drills. Drilling rates and normal forces demonstrate the ease of machining of these materials. The preliminary information on the relationship between microstructures and properties are provided. The mechanism of material removal is also discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.