Fabrication, properties, and modelling of engineering ceramics reinforced with nanoparticles of silicon carbide

The present paper, prepared by Professor R. W. Davidge, briefly summarises the results obtained from a multinational project aimed at assessing nanocomposite ceramics reinforced with fine (similar to 200 nm) particles of SiC. Various fabrication procedures were developed e.g. by attritor milling in a water medium, followed by freeze drying and hot pressing. Matrixes were alumina, silicon nitride, mullite, and cordierite. Although modest improvements in properties were obtained for all systems, the most interesting effects were observed for alumina. For a given grain size, strength was increased by similar to 70% and toughness by similar to 10% in material with 5 vol.-%SiC, and for the range studied was relatively independent of nanophase content and particle size (10-400 nm). Based on microscopy observations and estimates of the Al2O3/SiC boundary fracture energy, it is postulated that a key feature of the nanocomposite effect is associated with a strongly increasing R curve behaviour over a small number of grain dimensions. The consequence is that fracture is predominantly transcrystalline, as opposed to intercrystalline for pure material. This gives the nanocomposite a significantly improved wear resistance. The material also showed good strength retention at high temperatures in corrosive atmospheres, and a considerably reduced creep rate.