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Submicron (or ‘nanocrystalline’) SiC-reinforced Al 2 O 3 matrix composites have been prepared by co-milling followed by hot-pressing at 1650 °C. Both intra- and intergranular SiC particles were present. The volume ratio for intra- to intergranular particles was approximately 30:70 for 6 vol% SiC composites and 20:80 for 12 vol% SiC composites. The intragranular SiC (50–200 nm) formed mainly by growth of the Al 2 O 3 matrix grains, while Zener pinning, mainly by the larger (200–300 nm) particles, was thought to effectively limit the Al 2 O 3 grain size. Approximately 15% toughening was achieved by incorporating 12 vol% SiC nanoparticles into the matrix. The intergranular particles provided most of the toughening, mainly through a SiC particle-attracted crack deflection mechanism and crack impediment. No evidence was found of toughening by the intragranular particles, although they did cause some grain refinement by dislocation sub-boundary formation. A mixed fracture mode was observed, changing to a mostly intergranular mode with increasing volume of SiC particles. |
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