Effect of sintering temperature and siliconcarbide fraction on density, mechanical properties and fracture mode of alumina-silicon carbide micro/nanocomposites

In this study Al2O3-SiC micro/nanocomposites have been fabricated by mixing alumina nanopowders and silicon carbide micro/nanopowders, followed by hot pressing at 1550, 1600, 1650 and 1700 degrees C. The density, mechanical properties and fracture mode of Al2O3-SiC composites containing different volume fractions (2.5%, 5%, 7.5%, 10% and 15%) of micro/nanoscale SiC particles were investigated and compared with those of alumina. The relative density of composites could reach values very close to theoretical density, especially after sintering at 1700 degrees C. However, relative density declined by increasing the SiC fraction at the same sintering temperature. The flexural strength of composites was best for sintering temperature of 1700 degrees C and showed a maximum of 545 MPa for Alumina-10% SiC sintered at 1700 degrees C. Hardness showed a remarkable increase by adding SiC and reached a pick of 22.6 GPa for Alumina-15% SiC. Fracture toughness and fracture mode of alumina and composites with 5%, 10% and 15% SiC sintered at 1700 degrees C were also investigated. Composites were tougher than alumina and the scanning electron microscopy observations showed that fracture mode changes from intergranular for alumina to transgranular for composites. Finally X-ray diffraction analysis could not detect any chemical reactions between Al2O3 and SiC particles. (C) 2012 Elsevier Ltd. All rights reserved.